The Impact of Dry Air on the Location of Tornado Outbreaks Associated with Landfalling Tropical Cyclones in the Atlantic Basin

THESIS

Presented in Partial Fulfillment of the Requirements for the Degree Master of Science in the Graduate School of The Ohio State University

Christian David Feliciano-Camacho

Graduate Program in Atmospheric Sciences

The Ohio State University

2016

Master's Examination Committee:

Jay S. Hobgood, “Advisor”

Jialin Lin

Copyrighted by

Christian David Feliciano-Camacho

2016

Abstract

Tropical cyclones that form in the Atlantic Basin are responsible for causing major disruptions across a wide range of industries from government policy to transportation and tourism. With the continuous growth of coastal cities continuing, there has been an increasing demand for the scientific community to accurately predict the tracks and intensities of tropical cyclones in order to mitigate disruptions and damages. Although the scientific community has made tremendous advances in forecasting the tracks of tropical cyclones, predicting intensity has proven to be incredibly challenging. What has proved to be equally as difficult is predicting tropical cyclones that are capable of producing tornado outbreaks. Tornadoes that form as a result of tropical cyclones represent a small percentage of total tornado reports and they are often weaker compared to their supercell counterparts from mid latitude systems. Even though these tornadoes are not as common or as severe as supercell tornadoes that occur over the Great Plains, they are a serious threat to life and property. Recently it has been shown that dry air may be used as an indicator to pinpoint the location of tornado outbreaks which could give forecasters more lead time in alerting the public. Dry air can increase convective available potential energy (CAPE) which can lead to stronger updrafts, or it can lead to skies remaining clear so that solar radiation can heat the surface, eroding away any convective inhibition. All tropical cyclones that have made landfall between 2000 and

2014, regardless of their intensity, that produced at least six tornadoes within a 24 hour ii period before or after landfall were analyzed to determine any distinguishable patterns between dry air intrusions and the location of the tornado outbreaks. Dry air intrusions were easily visible by locating steep gradients in relative humidity. Images of relative humidity were created in Matlab using the European Centre for Medium-Range Weather

Forecasts ERA-Interim reanalysis data for 700, 500, 400, and 300 hPa. Atmospheric soundings were used to analyze and verify if the observed conditions match what is being displayed by the reanalysis data. Finally, simple calculations were performed as well as an analysis on the location of the relative humidity gradients in order to separate each tropical cyclone into various groupings and to discover any noteworthy patterns or trends.

iii

Vita

June 2010 ...... Framingham High School

2014...... B.S. Atmospheric Science, State University

of New York at Albany

2014 to present ...... Graduate Teaching Associate, Department

of Geography, The Ohio State University

Fields of Study

Major Field: Atmospheric Sciences

Table of Contents

Abstract ...... ii

Vita ...... iiv

List of Tables ...... vi

List of Figures ...... vii

Chapter 1: Introduction ...... 1

Chapter 2: Methodology ...... 10

Chapter 3: Results ...... 13

Chapter 4: Tornado Statistics ...... 246

Chapter 5: Results & Discussion ...... 257

References ...... 266

List of Tables

Table 1. Comparison of average LCL height and dewpoint depression (8C) at various levels in storms with midlevel dry intrusions that produced outbreaks (qualifying), storms without midlevel dry intrusions that produced outbreaks (nonqualifying), and storms with midlevel dry intrusions that failed to produce outbreaks (null)...... 9

Table 2. Tropical cyclones associated with each group based on total number of tornadoes located under a RH gradient...... 255

Table 3. Tornado statistics calculated for each grouping ...... 256

Table 4. Examined tropical cyclones with an “X” denoting which level an RH gradient was found over at least one tornado outbreak ………………………………………….264

Table 5. Characterized location of the RH gradients associated with each tropical cyclone………………………………………………………………………………….265

List of Figures

Figure 1. Position and track of Tropical Storm Alberto 10-14 June, 2006 created by

NOAA and NHC. Image taken from National Hurricane Center tropical cyclone report...... 18

Figure 2. Relative humidity for 300, 400, 500, and 700 hPa for 1200 UTC on 12 June.

Images created using the European Centre for Medium-Range Weather Forecasts ERA-

Interim reanalysis data within Matlab. Warmer colors indicate dry air while cooler colors indicate moist air. Black star indicates the location of the tropical cyclone at the current time. Dots represent the location of the various tornadoes that spawned at that time...... 19

Figure 3. Relative humidity for 300, 400, 500, and 700 hPa for 0600 UTC on 13 June.

Images created using the European Centre for Medium-Range Weather Forecasts ERA-

Figure 4. Relative humidity for 300, 400, 500, and 700 hPa for 1200 UTC on 13 June.

Images created using the European Centre for Medium-Range Weather Forecasts ERA-

Figure 5. Atmospheric profile sounding for Jacksonville, Florida taken at 0000 UTC on

June 13. Sounding taken from the University of Wyoming Department of Atmospheric

Science sounding page ...... 22

Figure 6. Atmospheric profile sounding for Jacksonville, Florida taken at 1200 UTC on

June 13. Sounding was taken from the University of Wyoming Department of

Atmospheric Science sounding page...... 23

Figure 7. Relative humidity for 300, 400, 500, and 700 hPa for 1800 UTC on 13 June.

Images created using the European Centre for Medium-Range Weather Forecasts ERA-

Figure 8. Atmospheric profile sounding for Charleston, South Carolina taken at 1200

UTC on June 13. Sounding was taken from the University of Wyoming Department of

Atmospheric Science sounding page ...... 25

Figure 9. Best track positions for Tropical Storm Allison, 5-17 June 2001. Image taken from NCH tropical cyclone report...... 29

Figure 10. Relative humidity for 300, 400, 500, and 700 hPa for 0600 UTC on 11 June.

Images created using the European Centre for Medium-Range Weather Forecasts ERA-

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Figure 11. Relative humidity for 300, 400, 500, and 700 hPa for 1200 UTC on 11 June.

Images created using the European Centre for Medium-Range Weather Forecasts ERA-

Figure 12. Atmospheric profile sounding for Jacksonville, Florida taken at 1200 UTC on

June 11. Image was taken from the University of Wyoming Department of Atmospheric

Science sounding page...... 32

Figure 13. Atmospheric profile sounding for Jacksonville, Florida taken at 0000 UTC on

June 12. Image was taken from the University of Wyoming Department of Atmospheric

Science sounding page...... 33

Figure 14. Relative humidity for 300, 400, 500, and 700 hPa for 0000 UTC on 12 June.

Images created using the European Centre for Medium-Range Weather Forecasts ERA-

Figure 15. Best track positions for Tropical Storm Andrea, 5-7 June 2013...... 39

Figure 16. Atmospheric profile sounding for Miami, Florida taken at 0000 UTC on June

6. Image was taken from the University of Wyoming Department of Atmospheric

Science sounding page...... 40

Figure 17. Relative humidity for 300, 400, 500, and 700 hPa for 0600 UTC on 6 June.

Images created using the European Centre for Medium-Range Weather Forecasts ERA-

Figure 18. Atmospheric profile sounding for Tampa, Florida taken at 1200 UTC on June

6. Image was taken from the University of Wyoming Department of Atmospheric

Science sounding page...... 42

Figure 19 Atmospheric profile sounding for Tampa, Florida taken at 0000 UTC on June

7. Image was taken from the University of Wyoming Department of Atmospheric

Science sounding page ...... 43

Figure 20. Relative humidity for 300, 400, 500, and 700 hPa for 1800 UTC on 16 June.

Images created using the European Centre for Medium-Range Weather Forecasts ERA-

Figure 21. Best track positions for Tropical Storm Bill, 29 June- 2 July, 2003. Track after landfall is based on analyses from the NOAA Hydrometeorological Prediction

Center ...... 47

Figure 22. Atmospheric profile sounding for Slidell Muni, Louisiana taken at 1200 UTC on June 30. Image was taken from the University of Wyoming Department of

Atmospheric Science sounding page...... 48

Figure 23. Relative humidity for 300, 400, 500, and 700 hPa for 1800 UTC on 30 June.

Images created using the European Centre for Medium-Range Weather Forecasts ERA-

Figure 24. Relative humidity for 300, 400, 500, and 700 hPa for 0000 UTC on 1 July.

Images created using the European Centre for Medium-Range Weather Forecasts ERA-

Figure 25. Atmospheric profile sounding for Tallahassee, Florida taken at 0000 UTC on

July 1. Image was taken from the University of Wyoming Department of Atmospheric

Science sounding page...... 51

Figure 26. Best track positions for Bonnie, 3-13 August, 2004. Track after landfall stage is based on analyses from the NOAA Hydrometeorological Prediction Center

(HPC)...... 55

Figure 27. Atmospheric profile sounding for Jacksonville, Florida taken at 1800 UTC on

Aug 12. Image was taken from the University of Wyoming Department of Atmospheric

Science sounding page ...... 56

Figure 28. Atmospheric profile sounding for Charleston, South Carolina taken at 1800

UTC on Aug 12. Image was taken from the University of Wyoming Department of

Atmospheric Science sounding page ...... 57

Figure 29. Relative humidity for 300, 400, 500, and 700 hPa for 1800 UTC on 12 Aug.

Images created using the European Centre for Medium-Range Weather Forecasts ERA-

Figure 30. Relative humidity for 300, 400, 500, and 700 hPa for 0600 UTC on 13 Aug.

Images created using the European Centre for Medium-Range Weather Forecasts ERA-

Figure 31. Best track positions for Hurricane Charley, 9-14 August 2004…………...…64

Figure 32. Relative humidity for 300, 400, 500, and 700 hPa for 1800 UTC on 13 Aug.

Images created using the European Centre for Medium-Range Weather Forecasts ERA-

Figure 33. Atmospheric profile sounding for Tampa, Florida taken at 1800 UTC on Aug

13. Image was taken from the University of Wyoming Department of Atmospheric

Science sounding page ...... 66

Figure 34. Atmospheric profile sounding for Miami, Florida taken at 1800 UTC on Aug

13. Image was taken from the University of Wyoming Department of Atmospheric

Science sounding page ...... 67

Figure 35. Relative humidity for 300, 400, 500, and 700 hPa for 1800 UTC on 14 Aug.

Images created using the European Centre for Medium-Range Weather Forecasts ERA-

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Figure 36. Atmospheric profile sounding for Newport, North Carolina taken at 1800 UTC on Aug 14. Image was taken from the University of Wyoming Department of

Atmospheric Science sounding page ...... 69

Figure 37. Best track positions for Hurricane Cindy, 3-7 July 2005. Track during the extratropical stage is based on analyses from the NOAA Hydrometeorological Prediction

Center ...... 75

Figure 38. Relative humidity for 300, 400, 500, and 700 hPa for 0600 UTC on July 6th.

Images created using the European Centre for Medium-Range Weather Forecasts ERA-

Figure 39. Atmospheric profile sounding for Tallahassee, Florida taken at 0000 UTC on

July 06. Image was taken from the University of Wyoming Department of Atmospheric

Science sounding page ...... 77

Figure 40. Atmospheric profile sounding for Tallahassee, Florida taken at 1200 UTC on

July 06. Image was taken from the University of Wyoming Department of Atmospheric

Science sounding page ...... 78

Figure 41. Relative humidity for 300, 400, 500, and 700 hPa for 1800 UTC on July 6th.

Images created using the European Centre for Medium-Range Weather Forecasts ERA-

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Figure 42. Relative humidity for 300, 400, 500, and 700 hPa for 0000 UTC on July 7th.

Images created using the European Centre for Medium-Range Weather Forecasts ERA-

Figure 43. Best track positions for Hurricane Dolly, 20-25 July 2008. Track during the inland tropical depression stage is based partially on analyses from the NOAA

Hydrometeorological Prediction Center ...... 84

Figure 44. Relative humidity for 300, 400, 500, and 700 hPa for 1800 UTC on 23 July.

Images created using the European Centre for Medium-Range Weather Forecasts ERA-

Figure 45. Atmospheric profile sounding for Corpus Christi, Texas taken at 1800 UTC on

July 23. Image was taken from the University of Wyoming Department of Atmospheric

Science sounding page ...... 86

Figure 46. Best track positions for Tropical Storm Fay, 5-11 September 2002, with minimum central pressure ...... 90

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Figure 47. Relative humidity for 300, 400, 500, and 700 hPa for 0000 UTC on 7

September. Images created using the European Centre for Medium-Range Weather

Forecasts ERA-Interim reanalysis data within Matlab. Warmer colors indicate dry air while cooler colors indicate moist air. Black star indicates the location of the tropical cyclone at the current time. Dots represent the location of the various tornadoes that spawned at that time...... 91

Figure 48. Atmospheric profile sounding for Corpus Christi, Texas taken at 0000 UTC on

September 7. Image was taken from the University of Wyoming Department of

Atmospheric Science sounding page ...... 92

Figure 49. Atmospheric profile sounding for Corpus Christi, Texas taken at 0000 UTC on

September 8. Image was taken from the University of Wyoming Department of

Atmospheric Science sounding page ...... 93

Figure 50. Relative humidity for 300, 400, 500, and 700 hPa for 0600 UTC on 8

September. Images created using the European Centre for Medium-Range Weather

Figure 51. Best track positions for Tropical Storm Fay, 15-26 August 2008. Track positions during the inland tropical depression and extratropical stages are based on a blend of analyses from the NOAA Hydrometeorological Prediction Center and the

National Hurricane Center ...... 99

Figure 52. Relative humidity for 300, 400, 500, and 700 hPa for 1800 UTC on 18 Aug.

Images created using the European Centre for Medium-Range Weather Forecasts ERA-

Figure 53. Atmospheric profile sounding for Miami, Florida taken at 1200 UTC on Aug

19. Image was taken from the University of Wyoming Department of Atmospheric

Science sounding page ...... 101

Figure 54. Relative humidity for 300, 400, 500, and 700 hPa for 1200 UTC on 19 Aug.

Images created using the European Centre for Medium-Range Weather Forecasts ERA-

Figure 55. Atmospheric profile sounding for Jacksonville, Florida taken at 1200 UTC on

Aug 22. Image was taken from the University of Wyoming Department of Atmospheric

Science sounding page ...... 103

Figure 56. Relative humidity for 300, 400, 500, and 700 hPa for 1800 UTC on 22 Aug.

Images created using the European Centre for Medium-Range Weather Forecasts ERA-

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Figure 57. Best track positions for Hurricane Frances, 25 August – 8 September

2004...... 113

Figure 58. Relative humidity for 300, 400, 500, and 700 hPa for 0000 UTC on 5

September. Images created using the European Centre for Medium-Range Weather

Figure 59. Atmospheric profile sounding for Jacksonville, Florida taken at 0000 UTC on

September 05. Image was taken from the University of Wyoming Department of

Atmospheric Science sounding page ...... 115

Figure 60. Atmospheric profile sounding for Miami, Florida taken at 0000 UTC on

September 5. Image was taken from the University of Wyoming Department of

Atmospheric Science sounding page ...... 116

Figure 61. Relative humidity for 300, 400, 500, and 700 hPa for 1800 UTC on 5

September. Images created using the European Centre for Medium-Range Weather

Figure 62. Relative humidity for 300, 400, 500, and 700 hPa for 1200 UTC on 6

September. Images created using the European Centre for Medium-Range Weather

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Figure 63. Relative humidity for 300, 400, 500, and 700 hPa for 1800 UTC on 6

September. Images created using the European Centre for Medium-Range Weather

Figure 64. Relative humidity for 300, 400, 500, and 700 hPa for 0600 UTC on 7

September. Images created using the European Centre for Medium-Range Weather

Figure 65. Atmospheric profile sounding for Charleston, South Carolina taken at 0000

UTC on September 7. Image was taken from the University of Wyoming Department of

Atmospheric Science sounding page ...... 121

Figure 66. Atmospheric profile sounding for Charleston, South Carolina taken at 1200

UTC on September 7. Image was taken from the University of Wyoming Department of

Atmospheric Science sounding page ...... 122

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Figure 67. Relative humidity for 300, 400, 500, and 700 hPa for 1200 UTC on 7

September. Images created using the European Centre for Medium-Range Weather

Figure 68. Best track positions for Hurricane Gabrielle, 11-19 September 2001. Track during the extratropical stage (after 19/0000 UTC) is based on analyses from the NOAA

Marine Prediction Center. Inset is an enlargement of loop over southeastern Gulf of

Mexico ...... 127

Figure 69. Relative humidity for 300, 400, 500, and 700 hPa for 0600 UTC on 14

September. Images created using the European Centre for Medium-Range Weather

Figure 70. Atmospheric profile sounding for Tampa, Florida taken at 0600 UTC on

September 14. Image was taken from the University of Wyoming Department of

Atmospheric Science sounding page ...... 129

Figure 71. Relative humidity for 300, 400, 500, and 700 hPa for 1800 UTC on 14

September. Images created using the European Centre for Medium-Range Weather

Forecasts ERA-Interim reanalysis data within Matlab. Warmer colors indicate dry air

xix while cooler colors indicate moist air. Black star indicates the location of the tropical cyclone at the current time. Dots represent the location of the various tornadoes that spawned at that time...... 130

Figure 72. Best track positions for Hurricane Gustav, 25 August – 4 September 2008.

Track during the extratropical stage is based on analyses from the NOAA

Hydrometeorological Prediction Center ...... 135

Figure 73. Relative humidity for 300, 400, 500, and 700 hPa for 1200 UTC on 1

September. Images created using the European Centre for Medium-Range Weather

Figure 74. Atmospheric profile sounding for Tallahassee, Florida taken at 1200 UTC on

September 1. Image was taken from the University of Wyoming Department of

Atmospheric Science sounding page ...... 137

Figure 75. Relative humidity for 300, 400, 500, and 700 hPa for 1800 UTC on 1

September. Images created using the European Centre for Medium-Range Weather

Figure 76. Relative humidity for 300, 400, 500, and 700 hPa for 1200 UTC on 2

September. Images created using the European Centre for Medium-Range Weather

Figure 77. Atmospheric profile sounding for Jackson, Mississippi taken at 1200 UTC on

September 2. Image was taken from the University of Wyoming Department of

Atmospheric Science sounding page ...... 140

Figure 78. Atmospheric profile sounding for Tallahassee, Florida taken at 1200 UTC on

September 2. Image was taken from the University of Wyoming Department of

Atmospheric Science sounding page ...... 141

Figure 79. Best track positions for Hurricane Ike, 1 – 14 September 2008. Track during the extratropical stage is based on analyses from the NOAA Hydrometeorological

Prediction Center and Environment Canada ...... 147

Figure 80. Relative humidity for 300, 400, 500, and 700 hPa for 1800 UTC on 12

September. Images created using the European Centre for Medium-Range Weather

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Figure 81. Atmospheric profile sounding for Lake Charles, Louisiana taken at 1800 UTC on September 12. Image was taken from the University of Wyoming Department of

Atmospheric Science sounding page ...... 149

Figure 82. Relative humidity for 300, 400, 500, and 700 hPa for 1200 UTC on 13

September. Images created using the European Centre for Medium-Range Weather

Figure 83. Atmospheric profile sounding for Lake Charles, Louisiana taken at 1200 UTC on September 13. Image was taken from the University of Wyoming Department of

Atmospheric Science sounding page ...... 151

Figure 84. Atmospheric profile sounding for Shreveport, Louisiana taken at 1200 UTC on

September 13. Image was taken from the University of Wyoming Department of

Atmospheric Science sounding page ...... 152

Figure 85. Relative humidity for 300, 400, 500, and 700 hPa for 1800 UTC on 13

September. Images created using the European Centre for Medium-Range Weather

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Figure 86. Best track positions for Hurricane Irene, 21 -28 August 2011. Track during the extratropical stage is based on analyses from the NOAA Hydrometeorological Prediction

Center ...... 158

Figure 87. Relative humidity for 300, 400, 500, and 700 hPa for 0000 UTC on August

26th. Images created using the European Centre for Medium-Range Weather Forecasts

ERA-Interim reanalysis data within Matlab. Warmer colors indicate dry air while cooler colors indicate moist air. Black star indicates the location of the tropical cyclone at the current time. Dots represent the location of the various tornadoes that spawned at that time ...... 159

Figure 88. Atmospheric profile sounding for Newport, North Carolina taken at 0000 UTC on August 26. Image was taken from the University of Wyoming Department of

Atmospheric Science sounding page ...... 160

Figure 89. Relative humidity for 300, 400, 500, and 700 hPa for 1200 UTC on August

27th. Images created using the European Centre for Medium-Range Weather Forecasts

Figure 90. Atmospheric profile sounding for Wallops Island, Virginia taken at 1200 UTC on August 27. Image was taken from the University of Wyoming Department of

Atmospheric Science sounding page ...... 162

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Figure 91. Relative humidity for 300, 400, 500, and 700 hPa for 0600 UTC on August

28th. Images created using the European Centre for Medium-Range Weather Forecasts

Figure 92. Best track positions for Hurricane Ivan, 2-24 September 2004 ...... 171

Figure 93. Relative humidity for 300, 400, 500, and 700 hPa for 1800 UTC on September

15th. Images created using the European Centre for Medium-Range Weather Forecasts

Figure 94. Atmospheric profile sounding for Slidell Muni, Louisiana taken at 1800 UTC on September 15. Image was taken from the University of Wyoming Department of

Atmospheric Science sounding page ...... 173

Figure 95. Atmospheric profile sounding for Tallahassee, Florida taken at 1800 UTC on

September 15. Image was taken from the University of Wyoming Department of

Atmospheric Science sounding page ...... 174

Figure 96. Relative humidity for 300, 400, 500, and 700 hPa for 0000 UTC on September

16th. Images created using the European Centre for Medium-Range Weather Forecasts

ERA-Interim reanalysis data within Matlab. Warmer colors indicate dry air while cooler

xxiv colors indicate moist air. Black star indicates the location of the tropical cyclone at the current time. Dots represent the location of the various tornadoes that spawned at that time ...... 175

Figure 97. Atmospheric profile sounding for Tampa, Florida taken at 0000 UTC on

September 16. Image was taken from the University of Wyoming Department of

Atmospheric Science sounding page ...... 176

Figure 98. Relative humidity for 300, 400, 500, and 700 hPa for 0600 UTC on September

16th. Images created using the European Centre for Medium-Range Weather Forecasts

Figure 99. Atmospheric profile sounding for Tallahassee, Florida taken at 0000 UTC on

September 16. Image was taken from the University of Wyoming Department of

Atmospheric Science sounding page ...... 178

Figure 100. Atmospheric profile sounding for Tallahassee, Florida taken at 1200 UTC on

September 16. Image was taken from the University of Wyoming Department of

Atmospheric Science sounding page ...... 179

Figure 101. Relative humidity for 300, 400, 500, and 700 hPa for 1800 UTC on

September 16th. Images created using the European Centre for Medium-Range Weather

Forecasts ERA-Interim reanalysis data within Matlab. Warmer colors indicate dry air while cooler colors indicate moist air. Black star indicates the location of the tropical

xxv cyclone at the current time. Dots represent the location of the various tornadoes that spawned at that time...... 180

Figure 102. Best track positions for Hurricane Jeanne, 13-28 September 2004 ...... 184

Figure 103. Relative humidity for 300, 400, 500, and 700 hPa for 0000 UTC on

September 26. Images created using the European Centre for Medium-Range Weather

Figure 104. Atmospheric profile sounding for Jacksonville, Florida taken at 0000 UTC on

September 26th. Image was taken from the University of Wyoming Department of

Atmospheric Science sounding page ...... 186

Figure 105. Atmospheric profile sounding for Miami, Florida taken at 0000 UTC on

September 26th. Image was taken from the University of Wyoming Department of

Atmospheric Science sounding page ...... 187

Figure 106. Relative humidity for 300, 400, 500, and 700 hPa for 1800 UTC on

September 26. Images created using the European Centre for Medium-Range Weather

xxvi

Figure 107. Atmospheric profile sounding for Charleston, South Carolina taken at 1800

UTC on September 26th. Image was taken from the University of Wyoming Department of Atmospheric Science sounding page ...... 189

Figure 108. Atmospheric profile sounding for Jacksonville, Florida taken at 1800 UTC on

September 26th. Image was taken from the University of Wyoming Department of

Atmospheric Science sounding page ...... 190

Figure 109. Best track positions for Hurricane Katrina, 23-30 August 2005 ...... 197

Figure 110. Relative humidity for 300, 400, 500, and 700 hPa for 1800 UTC on 28

August. Images created using the European Centre for Medium-Range Weather Forecasts

Figure 111. Atmospheric profile sounding for Tallahassee, Florida taken at 1800 UTC on

August 28th. Image was taken from the University of Wyoming Department of

Atmospheric Science sounding page ...... 199

Figure 112. Atmospheric profile sounding for Slidell Muni, Louisiana taken at 1800 UTC on August 28th. Image was taken from the University of Wyoming Department of

Atmospheric Science sounding page ...... 200

Figure 113. Relative humidity for 300, 400, 500, and 700 hPa for 1200 UTC on 29

August. Images created using the European Centre for Medium-Range Weather Forecasts

ERA-Interim reanalysis data within Matlab. Warmer colors indicate dry air while cooler

xxvii colors indicate moist air. Black star indicates the location of the tropical cyclone at the current time. Dots represent the location of the various tornadoes that spawned at that time ...... 201

Figure 114. Atmospheric profile sounding for Jackson, Mississippi taken at 1200 UTC on

August 29th. Image was taken from the University of Wyoming Department of

Atmospheric Science sounding page ...... 202

Figure 115. Relative humidity for 300, 400, 500, and 700 hPa for 1800 UTC on 29

August. Images created using the European Centre for Medium-Range Weather Forecasts

Figure 116. Relative humidity for 300, 400, 500, and 700 hPa for 0000 UTC on 30

August. Images created using the European Centre for Medium-Range Weather Forecasts

Figure 117. Atmospheric profile sounding for Peachtree City, Georgia taken at 0000 UTC on August 30th. Image was taken from the University of Wyoming Department of

Atmospheric Science sounding page ...... 205

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Figure 118. Best track positions for Tropical Storm Lee, 2-5 September 2011. Track during the extratropical stage is partially based on analyses from the NOAA

Hydrometeorological Prediction Center ...... 210

Figure 119. Relative humidity for 300, 400, 500, and 700 hPa for 1800 UTC on 3

September. Images created using the European Centre for Medium-Range Weather

Figure 120. Relative humidity for 300, 400, 500, and 700 hPa for 0600 UTC on 4

September. Images created using the European Centre for Medium-Range Weather

Figure 121. Atmospheric profile sounding for Slidell Muni, Louisiana taken at 0000 UTC on September 4th. Image was taken from the University of Wyoming Department of

Atmospheric Science sounding page ...... 213

Figure 122. Atmospheric profile sounding for Slidell Muni, Louisiana taken at 1200 UTC on September 4th. Image was taken from the University of Wyoming Department of

Atmospheric Science sounding page ...... 214

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Figure 123. Relative humidity for 300, 400, 500, and 700 hPa for 1800 UTC on 4

September. Images created using the European Centre for Medium-Range Weather

Figure 124. Best track positions for Hurricane Lili, 21 September - 4 October 2002 .... 219

Figure 125. Relative humidity for 300, 400, 500, and 700 hPa for 1200 UTC on 03

October. Images created using the European Centre for Medium-Range Weather

Figure 126. Atmospheric profile sounding for Lake Charles, Louisiana taken at 1200

UTC on October 3rd. Image was taken from the University of Wyoming Department of

Atmospheric Science sounding page ...... 221

Figure 127. Relative humidity for 300, 400, 500, and 700 hPa for 1800 UTC on 03 october. Images created using the European Centre for Medium-Range Weather

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Figure 128. Best track positions for Hurricane Rita, 18-26 September 2005 ...... 228

Figure 129. Relative humidity for 300, 400, 500, and 700 hPa for 1200 UTC on 24

September. Images created using the European Centre for Medium-Range Weather

Figure 130. Atmospheric profile sounding for Shreveport, Louisiana taken at 1200 UTC on September 24. Image was taken from the University of Wyoming Department of

Atmospheric Science sounding page ...... 230

Figure 131. Atmospheric profile sounding for Jackson, Mississippi taken at 1200 UTC on

September 24. Image was taken from the University of Wyoming Department of

Atmospheric Science sounding page ...... 231

Figure 132. Relative humidity for 300, 400, 500, and 700 hPa for 1800 UTC on 24

September. Images created using the European Centre for Medium-Range Weather

Figure 133. Atmospheric profile sounding for Jackson, Mississippi taken at 1800 UTC on

September 24. Image was taken from the University of Wyoming Department of

Atmospheric Science sounding page ...... 233

xxxi

Figure 134. Relative humidity for 300, 400, 500, and 700 hPa for 0000 UTC on 25

September. Images created using the European Centre for Medium-Range Weather

Figure 135. Atmospheric profile sounding for Slidell Muni, Louisiana taken at 0000 UTC on September 25. Image was taken from the University of Wyoming Department of

Atmospheric Science sounding page ...... 235

Figure 136. Atmospheric profile sounding for Little Rock, Arkansas taken at 0000 UTC on September 25. Image was taken from the University of Wyoming Department of

Atmospheric Science sounding page ...... 236

Figure 137. Relative humidity for 300, 400, 500, and 700 hPa for 0600 UTC on 25

September. Images created using the European Centre for Medium-Range Weather

Figure 138. Best track positions for Hurricane Wilma, October 2005. Track during the extratropical stage is partially based on analyses from the NOAA Ocean Prediction

Center ...... 241

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Figure 139. Relative humidity for 300, 400, 500, and 700 hPa for 1800 UTC on 23

October. Images created using the European Centre for Medium-Range Weather

Figure 140. Atmospheric profile sounding for Tampa, Florida taken at 1800 UTC on

October 23. Image was taken from the University of Wyoming Department of

Atmospheric Science sounding page ...... 243

Figure 141. Atmospheric profile sounding for Miami, Florida taken at 1800 UTC on

October 23. Image was taken from the University of Wyoming Department of

Atmospheric Science sounding page ...... 244

Figure 142. Relative humidity for 300, 400, 500, and 700 hPa for 0600 UTC on 24

October. Images created using the European Centre for Medium-Range Weather

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Chapter 1: Introduction

Tropical cyclones in the Atlantic Basin are responsible for major disruptions across a wide range of industries from government policy to transportation and tourism.

With the growth of coastal cities continuing, there has been an increasing demand for the scientific community to accurately predict tropical cyclone track and intensities in order to mitigate disruptions and damages. Although the scientific community has made tremendous advances in predicting the tracks of tropical cyclones with increasing skill, predicting the intensity with the same amount of skill has proven to be incredibly challenging. What has proved to be equally as difficult is predicting which tropical cyclones are capable of producing wide spread tornado outbreaks. Tropical cyclone tornadoes represent a small percentage of total tornado reports (Edward 2010) and are often weaker compared to their supercell counterparts from mid latitude systems. Even though tropical cyclone tornadoes are not as common or severe as supercell tornadoes that occur over the Great Plains they are a legitimate threat to life and property with any tropical cyclone that threatens landfall in the U.S.

This threat has sparked numerous studies over several decades exploring the structure and characteristics of tropical cyclone tornadoes in hopes of being able to answer the ultimate question of why some tropical cyclones produce tornadoes and others do not. Edwards (2012) composed a paper titled “Tropical Cyclone Tornadoes: A Review 1 of Knowledge in Research and Prediction” that summarizes in great detail tropical cyclone tornado research that will be discussed below. Edwards explains how tornado reports have increased drastically over the past few decades and with the introduction of the WSR-88D radar system researchers and surveyors are able to better classify the strength of tropical cyclone tornadoes. Schultz and Cecil (2009) performed a tornado occurrence analysis between 1950 and 2007. There results indicated that out of all the tropical cyclones producing tornadoes during the study period, 81.1% were classified as

“weak” (F0-F1), 13.8% were “strong” (F2-F3) and less than 1% were “violent” (F4, no

F5). This reinforced the idea that tropical cyclone tornadoes are often weaker and smaller in size as noted by Fujita in his survey of Japanese typhoon tornadoes (Fujita 1972).

Supercells in tropical cyclones have been found to not only have a smaller mesocyclone but the associated vertical vorticity is confined to the lowest 5 kilometers as well (Suzuki

2010) leading to weaker tornadoes.

It is important to note that before radar was implemented there was an overestimation of tornadoes classified as F2/EF2 or above. As a result Schultz and Cecil broke down the data into time periods before and after national deployment of the WSR-

88D and found a sharp decrease in violent tornadoes with a corresponding spike in the amount of weak F0/F1 tornadoes. A more recent studied using the current warning and verification system of the Enhanced Fujita Scale by Edwards (2010) has revealed an increase in EF0-EF1 tornadoes.

Understanding the spatial distribution of tropical cyclone tornadoes is another area that has made tremendous advancements as noted by Edwards. Smith (1965) states

2 that the majority of tornadoes occurred in the right front quadrant of the storm relative to motion. Smith reported that about 51% of tropical cyclone tornadoes between 1955 and

1962 occurred in the right front quadrant with the other 49 percent scattered throughout the other quadrants. Studies performed by Pearson and Sadowski (1965) as well as Fujita

(1972) reflected similar results. It was not until McCaul (1991) noticed that not only was the right front quadrant the favorable location for tropical cyclone tornado development, but that the majority of the scattering of the tornadoes not in the right front quadrant were located towards the rear of the storm relative to motion. There has also been research indicating that most tropical cyclone tornadoes occur in the north east sector of the storm regardless of the storm motion (north based frame of reference). Edwards notes in his tropical cyclone tornado literature review (2012) that both the north-based and storm relative frames of reference are often used interchangeably. Edwards proposes that the use of strict quadrants should be discouraged and that a loosely defined sector should be used. For example, in the Northern Hemisphere most tropical cyclone tornadoes should occur in the sector of the storm towards the north-northwest through northeast, and down to the southeast of the storm center. This is an interesting idea that requires additional research before it can be deployed into operation use by forecasters and emergency management officials.

Contrary to the methods discussed above Edwards explains how Molinari and

Vollaro (2008) used a shear-relative framework to examine the convective cell-relative helicity. Helicity is a severe weather variable that is widely used in forecasting environments favorable for the development of tornadic supercells. Helicity values have

3 been shown to be weak in tropical cyclone tornado environments (Johns 1993). Molinari and Vollaro calculated helicity values for Tropical Storm Bonnie (1998) to analyze which quadrant/sector was more suitable for tornadic supercells to develop. Due to very limited radar data available Molinari and Vollaro used dropsonde data and implemented them into common cell motion algorithms used for midlatitude supercells. The largest values of helicity were located in the downshear-left quadrant of Tropical Storm Bonnie. This translated to the northeast section of the storm using the north based frame of reference as well as the right front quadrant of the cyclone relative to the storms motion (Edwards

2012). Similar results were found when the sample size was increased to eight tropical cyclones. One concern however, is that due to the size of landfalling tropical cyclones, it is often unclear where to collect and analyze shear vector data.

Tropical cyclone climatology has shown that the majority of tropical cyclone tornadoes occur in the region 100-500 km from the center. Studies have also shown that there is a decrease in tornado strength as one move towards the eye of the storm

(Edwards 2012). This does not mean that tropical cyclone tornadoes cannot develop within 100 km of the storm center as seen in climatologies from Gentry (1983) and

McCaul (1991). However, as noted by Edwards, there have been no verified observations of tornadoes touching down near the eyewall. Wakimoto and Black (1994) inferred eyewall tornadoes based on damage that was restricted to narrow “corridors”; however, other potential sources of the damage cannot be ruled out. Fujita documented what he called “mini-swirls” created by various shear processes inside of the eyewall in hurricane

Andrew but was very hesitant to call these swirls tornadoes. Powell and Houston (1996)

4 questioned if the damage observed by Fujita in Hurricane Andrew was caused by a strong downburst. Due to the violent nature of the eyewall, verification of eye wall tornadoes still eludes researchers today. However, with better technology and radar available today it would be interesting to reinvestigate these events to develop a better understanding of the process occurring in the eyewall to determine if tornadoes are even possible within

100 km of the storm center.

There have been however, a few recent studies which have begun to answer this question. It is well documented that tornadoes occur in the outer rainbands. There seem to be three major factors that lead to this result. Although the strongest winds are located near the eyewall of a mature hurricane, the vertical wind shear necessary for tornado development decreases (McCaul 1991, Molinari and Vollaro 2008). Edwards et al. (2012) also showed that convection near the eye of a hurricane tended to be non supercellular.

Finally McCaul (1991) conveyed that there is a decrease in convective available potential energy (CAPE) as one moved towards the storm center. The heavy rain and dense cloud cover found near the eyewall limits daytime heating that promotes buoyancy which leads to the diurnal peak in tornadoes (Edwards 2012). This afternoon peak in tornado activity corresponds to the erosion of any convection inhibition found at the surface as well as steepens lapse rates increasing CAPE values. Even with this peak a large number of tropical cyclone tornadoes occur at night. McCaul showed that more than half of tropical cyclone tornadoes in his studied spawned between 1400-2300 UTC local time in the southeast United States. This indicated that factors other than daytime heating were in

5 play as tropical cyclone tornado environments remained favorable well into the evening hours (Edward 2012).

As knowledge of tornado distribution and strength grew, researchers began to shift their attention to determine which factors in the atmosphere could influence tornado development from the synoptic scale all the way down to the mesoscale. It has been shown that using the same ingredients of lift, instability, moisture, and shear, which are used to determine favorable environments for supercell development, can be applied to tornado forecasting for tropical cyclones (Johns and Doswell 1992). Due to the large amount of moisture in tropical cyclones the main factors influencing tornado development must be a combination of shear, instability, and boundaries to provide ample lift (Edwards 2012).

Researchers began to look for any large scale synoptic patterns that might influence tornado development in tropical cyclones. Since states that border the Gulf of

Mexico and the Atlantic coast are located in between the tropics and the mid-latitudes, tropical cyclones that enter this region are often influenced greatly by mid-latitude weather systems that influence structure and strength (Edwards 2012). Numerous papers have shown that as tropical cyclones approach the United States they enter regions of enhanced shear which helps provide the necessary rotation for tornado formation

(McCaul 1991, Verbout et al. 2007, Molinari and Vollaro 2010). Westerly winds also help to re-curve tropical cyclones back towards the northeast. Verbout (2007) created composites of synoptic patters for tropical cyclones that made landfall in Texas. This study revealed that landfalling tropical cyclones yield the greatest amounts of tornadoes

6 when there is a 500 hPa trough in the central plains with the tropical cyclone in close proximity to the embedded jet streak. Also more tornadoes seemed to occur when there were greater 500 hPa geopotential height anomalies and increased height gradients

(Edwards 2012).

Mesoscale features are of great interest to researchers in that they may provide clues as to what makes an environment more suitable for tornadoes or give forecasters an early indication that a widespread tornado event is imminent. For example, supercell development in the outer rain bands has shown to contain a maximum in cloud-to-ground lighting (Molinari et al. 1999, Edwards 2012). Lightning production can be enhanced in supercells that contain very vigorous updrafts. Since an increase in lighting can indicate strong supercells and the fact that most tornadoes form in supercells forecasters can use this information to their advantage. Even though some supercells produce very little or no cloud-to-ground lighting (McCaul 2004) lightning trends can still be used to assess tornado potential in supercells that are embedded in tropical cyclone rain bands. At this time, however, there is just not enough data on this subject to determine whether this is a viable option for forecasters (Edwards 2012).

Another feature that has gained interest among scientists is the effects of dry air in the upper levels of the troposphere on tropical cyclone tornado development. Lon Curtis

(2004), in his paper, “Midlevel Dry Intrusions as a Factor in Tornado Outbreaks

Associated with Landfalling Tropical Cyclones from the Atlantic and Gulf of Mexico”, hints at the idea that tornado outbreaks occur under regions that have a sharp gradient in relative humidity at 700 hPa and/or 500 hPa. The tropical cyclones that Curtis examined

7 occurred during the years 1960-1999. However, with the strict criteria Curtis used all the tropical cyclones that did not make landfall in the United States and produced less than

20 tornadoes were eliminated. As a result only thirteen storms were left to be analyzed.

Curtis used radiosonde data to examine the dry intrusions at 500 hPa, 700 hPa, and 800 hPa 36 hours before and after landfall. Relative humidity images were also created to assist with the analysis. Analysis showed that, for 11 of the 13 storms examined, the tornado outbreak occurred under regions that had a strong gradient in relative humidity in the upper levels. The other two storms did produce a widespread tornado outbreak but did not show evidence that dry air aloft was a contributing factor.

Even though the 11 outbreaks also occurred during the diurnal peak in tropical cyclone tornado formation, the clear dry air intrusions are believed to play a significant role. It is believed that the dry air steepened the lapse rate, increasing CAPE, as well as increasing surface heating to make the environment more buoyant. How much the dry air steepens lapse rates aloft, however, was not studied in this paper and deserves further research.

With distinct evidence that tornado outbreak location correlated with locations of steep relative humidity gradients aloft, Curtis very briefly compares storm environments which had a dry intrusion that produced an outbreak, environments that had no dry intrusion yet produced outbreaks, and environments that had dry intrusions yet failed to produce an outbreak. Table 1 below shows that the qualifying storms had a much lower liquid condensation level compared to storms that did not produce outbreaks similar to findings by Rasmussen and Blanchard (1998). The table also shows how the qualifying storms were much drier above 700 hPa while the nonqualifying and null cases seemed to

8 be much drier below 700 hPa. It is however, important to notice that the sample size for this table is very small. Only 2 storms were considered nonqualifying while only one storm was considered null. The purpose of this paper is to determine if the level at which the dry intrusion is found really plays a role in whether or not there is a tornado outbreak.

A larger sample size can be achieved by relaxing the criteria imposed by Curtis. By looking at all landfalling tropical cyclones regardless of strength that have produced at least 6 tornadoes within a 24 hour period before or after landfall between the years 2000-

2014, any distinguishable patterns between dry air intrusions and location of the outbreak can be identified. Does a specific level tend to correlate RH gradients and the location of tornado outbreaks better than others? Are there any noteworthy characteristic or trends researchers and forecasters should be aware of? Is this a phenomena that only occurs with major hurricanes? Is it possible that a forecaster could look at the level of the dry intrusion to help determine the severity of a possible outbreak?

LCL Surface 925 850 800 700 600 500 (m) (hPa) (hPa) (hPa) (hPa) (hPa) (hPa) Qualifying 141 1.5 1.8 3.0 3.4 4.4 6.6 7.0 Nonqualifying 325 3.0 2.4 3.0 3.4 4.2 0.5 1.5 Null 215 1.2 4.7 3.9 6.5 4.0 2.5 1.6 Table 1. Comparison of average LCL height and dewpoint depression (8C) at various levels in storms with midlevel dry intrusions that produced outbreaks (qualifying), storms without midlevel dry intrusions that produced outbreaks (nonqualifying), and storms with midlevel dry intrusions that failed to produce outbreaks (null).

Chapter 2: Methodology

All relevant tropical cyclone information such as track, intensity, and number of tornadoes produced were collected from the National Hurricane Centers tropical cyclone reports. The number of tornadoes was crossed referenced with the Storm Predictions

Center National Severe Weather Database Browser. Data collection for this research project began by compiling a list of all tropical cyclones that made landfall in the United stated between the years 2000-2014. I used the tropical cyclone reports issued by NHC to eliminate any tropical cyclone that did not produce at least 6 tornadoes which is what is widely considered the minimum number of tornadoes needed for an outbreak (Galway

1977). Once the list is completed, tornado outbreak location for each qualifying storm was determined using the Storm Prediction Centers (SPC) National Severe Weather

Database Browser Severe Plot 3.0. Using Severe Plot 3.0, tornadoes occurring 24 hours before and after landfall were plotted. This online tool also allows for an accurate and efficient way to determine which tornadoes occurred outside the time frame specified above. At least 6 tornadoes need to have occurred during this timeframe to be considered. This timeframe is used in order to eliminate tornadoes that may have formed after a tropical cyclone had become extratropical. The latitude and longitude of each tornado was also recorded using data from the Tornado History Project. The Tornado

History Project is a searchable database of all reported U.S. tornadoes from 1950-2014. 10

Tornado data is verified and retrieved from the Storm Prediction Center and the National

Climatic Data Center historical tornado archives. The next step after pinpointing tornado outbreak location was to locate upper level dry air intrusions by creating images of relative humidity.

Dry air intrusions were easily visible by locating steep gradients in relative humidity. Images of relative humidity were created using the European Centre for

Medium-Range Weather Forecasts ERA-Interim reanalysis data within Matlab. This specific data set was used because it was a newer and higher quality data (80 km) set compared to other publicly available data sets suitable for this research project. Four panel images of relative humidity were contoured and plotted for 700, 500, 400, and 300 hPa for 0000, 0600, 1200, or 1800 UTC. The locations of each individual tornado as well as the center of the tropical cyclone was also plotted on the same image. To verify the accuracy of the reanalysis data observed soundings were obtained using the University of

Wyoming upper air soundings page. Soundings near the tornado outbreak from under the dry intrusion as well as from a more saturated environment away from the dry air were used to verify the location of any RH gradients found using the reanalysis data. Dew point depressions values for multiple levels were also calculated from the same soundings in order to capture a better understanding of how strong the various dry air intrusions were. However, the dew point depressions values were not included as they did not do as

11 good of a job portraying the magnitude of the dry air intrusion compared to a Skew-T diagram of the sounding.

Once these images were made I was able to determine which storms produced outbreaks in the same region that a dry air intrusion is located. Each tropical cyclone was then separated into one of six categories. The category in which each tropical cyclone was placed was determined by how many tornadoes associated with each tropical cyclone was located under an RH gradient in at least one of the four levels analyzed. Once all storms have been classified, various calculations with in each category were performed to determine notable trends. For example, how many tornadoes occurred before or after landfall with in each group? Were tornadoes that occurred after landfall more likely to have been located under an RH gradient compared to tornadoes that occurred before landfall? The relaxed criteria for qualifying tropical cyclones alongside the added focus on the upper levels should provide more conclusive results due to the larger sample size to support or contradict the initial findings by Curtis. The added calculations should also provide new noteworthy trends and patterns that were not discussed by Curtis in his initial paper.

Chapter 3: Results

3.1 Alberto (2006)

Tropical Storm Alberto first showed signs of organization on June 8th just off the

Yucatan Peninsula when an active weather pattern came into contact with a westward moving tropical wave. By June 10th the resulting convection showed enough organization as well as a surface circulation were the system was classified as a tropical depression.

The cyclone continued to move north of the Yucatan Peninsula into a region of increased wind shear. Although the increased southwesterly wind shear helped limit intensification by displacing the majority of the convention away from the center of circulation, the system was upgraded to a tropical storm by 0000 UTC on June 11th. Alberto then shifted to the northeast and set aim for Florida where organization continued until a peak intensity of 60 kts and a sea level pressure of 995 hPa was recorded 100 miles south of

Apalachicola, Florida by June 13th. Fortunately, Alberto began to weaken as it approached the Florida coast line. By the time Albert made landfall at 1630 UTC on June

13th near Adams Beach, Florida, winds speeds dropped to around 40 kts. Alberto continued to weaken as it moved across the state and eventually began to lose tropical characteristics by 1200 UTC 14 June near South Carolina. Thereafter, the system moved out into the Atlantic becoming a strong extra tropical system near Nova Scotia. The

13 remnants of Alberto were last tracked near the British Isles where it was absorbed by a frontal system. The track for Tropical Storm Alberto is shown in Figure 1.

Fortunately, the damage caused by Tropical Storm Alberto over the western

Caribbean as well as the United States was kept to a minimum largely impart to the systems relatively weak strength. Alberto caused widespread flooding especially over

Cuba where rainfall reports as high as 17 inches were recorded. Towns in Florida had flood water as high as three feet damaging homes, businesses, and covering roadways.

Tropical Storm Alberto also produced what Galway (Galway 1977) defines as a tornado outbreak. I define a tornado outbreak as a storm producing at least 6 tornadoes during the

24 hrs before or after landfall unlike Curtis who required 20 tornadoes. As a result Curtis was limited to a very small sample size. During the 24 hrs period before and after landfall

Tropical Storm Alberto produced an estimate of 15 tornadoes across Florida, Georgia, and South Carolina. All of the tornadoes except one were classified as EF 0 on the enhanced Fujita scale while one was classified as EF 1 which touched downed in

Chatham County near the Georgia/South Carolina boarder. Damage caused by the tornadoes was minimal according to NHC.

A total of six tornadoes occurred in Florida. The first three tornadoes occurred around 1200 UTC June 12th just southeast of Tampa, Florida. Atmospheric soundings for

Tampa and Miami (not shown) around the same time remain consistent with what is shown in the reanalysis data. The soundings show the atmosphere becoming less saturated as one moves southeast from Tampa towards Miami verifying the location of the RH gradient that the tornadoes did indeed spawn under at 700 hPa as seen in figure 2.

At this time the tornadoes occurred under a region where the RH at 700 hPa increased from 60-90%. There was very little if any gradients in RH at 300, 400, and 500 hPa.

The remaining three tornadoes that occurred in Florida were located around Jacksonville between 0600-0800 UTC June 13th. The relative humidity values fail to indicate an RH gradient over the area where the tornadoes occurred as show in figure 3. Figure 3 indicates that Jacksonville is under a region with relative humidity values at 80% or higher at 0600 UTC. The relative humidity gradient is displaced farther north and to the west. However, a dry slot becomes very evident at 1200 UTC. Figure 4 shows relative humidity at 1200 UTC June 13th. While the air remains saturated at 700 hPa there is a clear gradient in RH where the relative humidity goes from near 50% west of

Jacksonville to about 80% near the coast at 300, 400, and 500 hPa. Dry air can have many effects on the surrounding environment. The dry air aloft can help steepen lapse rates so that the surrounding environment is cooler then air parcels being lifted through it.

This can result in more CAPE which can lead to more vigorous updrafts which is a major component of convective storms. This can be seen in figure 5 and 1f which compares the atmospheric profile for 0000 UTC and 1200 UTC on the 13th for Jacksonville, Florida.

Since no 0600 UTC sounding was available 0000 and 1200 UTC were used instead.

Figure 5 is the 0000 UTC sounding which illustrates a very moist environment throughout the entire column with air cooling following the moist adiabatic lapse rate.

There is very little if any CAPE at all in this sounding as well as very little directional and speed wind shear. Figure 6 is the 1200 UTC sounding taken after the dry air moved into the area. A clear area of dry air can be seen between 600hPa and 300 hPa. CAPE

15 values have increased to 176 J/kg and the temperature has increased enough to remove some of the convective inhibition present in the 0000 UTC sounding. The dry air may also clear skies allowing solar radiation to heat the ground enough to produce thermals that can help lift parcels from the surface up into the regions with the steeper lapse rates.

While the value for CAPE is low it is important to note that the 1200 UTC sounding was taken just after the tornadoes touched down which could have resulted in the sounding sampling air that had already had energy consumed.

The final set of tornadoes occurred throughout eastern South Carolina and extreme northwest Georgia around 1800 UTC on June 13th. The relative humidity values for 1800 UTC (figure 7) show that there is indeed an RH gradient over the region. At this time RH values across the Georgia and South Carolina coastline increases from 20% in the South to 90% further north. The RH gradient at 500 hPa is the only level which incorporates all the tornadoes under the steep gradient. The RH gradient can still be seen at 400 hPa before becoming more saturated by 300hPa especially further north. The sounding for Charleston shows the extent of the dry slot which helped produced CAPE values higher than 500 J/kgK. However, a low level inversion cap and very little wind shear are present. The 0000 UTC sounding on June 14th (not shown) shows that between

1200 UTC and 0000 UTC the environment became more saturated similar to the 1800

UTC relative humidity images but the inversion cap was removed and CAPE values increased above 600 J/kg. Wind shear also increased which helped produce the EF 1 tornado that touched down around 1800 UTC.

Overall Tropical Storm Alberto showed a lot of evidence that agrees with the findings made by Curtis. All of the tornadoes except for three occurred under regions with a gradient of relative humidity. There was also a clear dry slot at various levels seen in the soundings. Based on the soundings it seems as if Charleston had a much more conducive environment for tornadoes to form in general compared to Jacksonville which might explain the discrepancies between the number of tornadoes that spawned between the two locations.

Figure 1. Position and track of Tropical Storm Alberto 10-14 June, 2006 created by NOAA and NHC. Image taken from National Hurricane Center tropical cyclone report.

Figure 2. Relative humidity for 300, 400, 500, and 700 hPa for 1200 UTC on 12 June. Images created using the European Centre for Medium-Range Weather Forecasts ERA- Interim reanalysis data within Matlab. Warmer colors indicate dry air while cooler colors indicate moist air. Black star indicates the location of the tropical cyclone at the current time. Dots represent the location of the various tornadoes that spawned at that time.

Figure 3. Relative humidity for 300, 400, 500, and 700 hPa for 0600 UTC on 13 June. Images created using the European Centre for Medium-Range Weather Forecasts ERA- Interim reanalysis data within Matlab. Warmer colors indicate dry air while cooler colors indicate moist air. Black star indicates the location of the tropical cyclone at the current time. Dots represent the location of the various tornadoes that spawned at that time.

Figure 4. Relative humidity for 300, 400, 500, and 700 hPa for 1200 UTC on 13 June. Images created using the European Centre for Medium-Range Weather Forecasts ERA- Interim reanalysis data within Matlab. Warmer colors indicate dry air while cooler colors indicate moist air. Black star indicates the location of the tropical cyclone at the current time. Dots represent the location of the various tornadoes that spawned at that time.

Figure 5. Atmospheric profile sounding for Jacksonville, Florida taken at 0000 UTC on June 13. Sounding taken from the University of Wyoming Department of Atmospheric Science sounding page.

Figure 6. Atmospheric profile sounding for Jacksonville, Florida taken at 1200 UTC on June 13. Sounding was taken from the University of Wyoming Department of Atmospheric Science sounding page.

Figure 7. Relative humidity for 300, 400, 500, and 700 hPa for 1800 UTC on 13 June. Images created using the European Centre for Medium-Range Weather Forecasts ERA- Interim reanalysis data within Matlab. Warmer colors indicate dry air while cooler colors indicate moist air. Black star indicates the location of the tropical cyclone at the current time. Dots represent the location of the various tornadoes that spawned at that time.

Figure 8. Atmospheric profile sounding for Charleston, South Carolina taken at 1200 UTC on June 13. Sounding was taken from the University of Wyoming Department of Atmospheric Science sounding page.

3.2 Allison (2001)

The piece of energy that would eventually become Tropical Storm Allison developed as a tropical wave off the west coast of Africa. Very little convection was associated with this wave as it moved west across the Atlantic eventually moving over

South America before it reformed over the southwestern Caribbean Sea on May 29th. It wasn’t until June 3rd that the system began to move out into over the Yucatan Peninsula and out into Gulf of Mexico were a relatively strong mid-level circulation was formed.

On June 5th deep convection began to develop as it began to interact with an upper level low centered over Texas. By 1200 UTC on the 5th there was enough evidence to upgrade the system in to a tropical storm about 120 n mi south of the Texas coastline. Allison’s pressure quickly began to drop causing winds to increase substantially over the Gulf of

Mexico. According to the NHC winds as high as 40 kts were recorded with gust up to 50 kts more than 200 n mi east of the center. Closer to the center of the storm a ship reported gust as high as 60 kts about 90 n mi east of the storm center. Data collected from the U.S.

Air Force Reserve reconnaissance flight along with the data from the ship indicated that

Allison had strengthened even further. The cyclone moved slowly to the north where it eventually made landfall near Freeport, Texas. The storm center moved right through the

Houston area before quickly weakening to a depression and becoming stationary over eastern Texas. The system attempted to redevelop as it moved over the gulf once again but dry air and strong wind shear prevented further development. However, a new low pressure center developed by 0000 UTC on June 11th eventually making landfall once

26 again near Morgan City, Louisiana as a subtropical depression. Figure 9 illustrates

Allison’s track as well as reformation over the gulf.

Eastern and southeastern Texas which included Houston experienced extremely heavy rainfall due to Allison’s slow track north as well as its return back to the Gulf of

Mexico. Some reports from the east side of Houston reported receiving more the 30 inches of rainfall. Residents in Galveston Island were forced to evacuate over flooding concerns from 2-3 foot high storm surge as well as waves as high as 8 feet. This flooding caused considerable beach erosion as well as some road damage. The heavy rainfall devastated the area with FEMA estimating the damages at 5 billion with 4.8 billion in

Houston alone. More than 40,000 homes and business were damaged impacting the local economy. Unfortunately, NHC labeled Allison as the deadliest and most costly tropical or subtropical storm on record in the U.S due to the 41 death directly related to the storm as well as the billions of dollars in damages.

Allison produced 23 tornadoes across much of the southeast United States. This paper will focus only on the first ten tornadoes as the rest occurred after Allison had already become extratropical. The first five tornadoes formed between 0600 UTC and

1200 UTC on June 11th near the southern Mississippi/Alabama coast. The majority of the tornadoes were rated F0 on the Fujita scale however, three tornadoes were rated F1 across Mississippi. Figure 2 shows the relative RH values for the four levels analyzed at

0600 UTC. The relative humidity images seem to indicate a gradient in RH far removed out towards the west of the outbreak region. All five tornadoes occur in a region where the RH is 90%+. The proximity of the core of the tropical cyclone could be the reason

27 why the environment was so saturated as the center was only about 250 km away. By

1200 UTC the RH gradient moves east at all levels as seen in figure 11. However, the RH gradient is still too far west which goes against the findings made by Curtis. The 0000

UTC sounding for LIX (not shown) indicates an environment saturated throughout the entire column agreeing with the analysis data shown below. The sounding for 1200 UTC on the same day (figure 12) begins to pick up on the dry air moving east matching what was seen in the reanalysis data. Even though the 1200 UTC sounding occurred after the initial tornadoes spawned it helps illustrate that even though dry air began to move east the column remained relatively saturated with the main gradient to far west of the outbreak region.

Five more tornadoes including an F1 in Florida occurred shortly after 0000 UTC on June 12th. The Jacksonville, Florida sounding (JAX) for 0000 UTC indicates layers of dry air between 700-600hPa, 550hPa, and 475hPa (figure 12). Unlike the first set of tornadoes that did not occur under a RH gradient the final five tornadoes seem to be incorporated by a steep RH gradient. The majority of the tornadoes occur in regions where the RH is 70%+ with a weak gradient nearby. At 500hPa however, three of the tornadoes occur in less saturated environments with a tighter gradient in RH aloft. To a lesser extent at 400 hPa the southern RH gradient also incorporates a few tornadoes right on its northern edge. Although these three tornadoes seem to occur under a RH gradient the majority of the ten tornadoes did not. As a result, using gradients in RH within

Tropical Storm Allison fails to accurately predict the location of the tornado outbreak.

Figure 9. Best track positions for Tropical Storm Allison, 5-17 June 2001. Image taken from NCH tropical cyclone report.

Figure 10. Relative humidity for 300, 400, 500, and 700 hPa for 0600 UTC on 11 June. Images created using the European Centre for Medium-Range Weather Forecasts ERA- Interim reanalysis data within Matlab. Warmer colors indicate dry air while cooler colors indicate moist air. Black star indicates the location of the tropical cyclone at the current time. Dots represent the location of the various tornadoes that spawned at that time.

Figure 11. Relative humidity for 300, 400, 500, and 700 hPa for 1200 UTC on 11 June. Images created using the European Centre for Medium-Range Weather Forecasts ERA- Interim reanalysis data within Matlab. Warmer colors indicate dry air while cooler colors indicate moist air. Black star indicates the location of the tropical cyclone at the current time. Dots represent the location of the various tornadoes that spawned at that time.

Figure 12. Atmospheric profile sounding for Jacksonville, Florida taken at 1200 UTC on June 11. Image was taken from the University of Wyoming Department of Atmospheric Science sounding page.

Figure 13. Atmospheric profile sounding for Jacksonville, Florida taken at 0000 UTC on June 12. Image was taken from the University of Wyoming Department of Atmospheric Science sounding page.

Figure 14. Relative humidity for 300, 400, 500, and 700 hPa for 0000 UTC on 12 June. Images created using the European Centre for Medium-Range Weather Forecasts ERA- Interim reanalysis data within Matlab. Warmer colors indicate dry air while cooler colors indicate moist air. Black star indicates the location of the tropical cyclone at the current time. Dots represent the location of the various tornadoes that spawned at that time.

3.3 Andrea (2013)

Tropical storm Andrea was the first and only storm to make landfall in the United

States during a relatively quiet Atlantic tropical cyclone season. Tropical Storm Andrea had a complicated beginning which all started when Hurricane Barbara in the Pacific became entangled in a large cyclonic gyre located over southeastern Mexico. A trough to the north formed which together helped create a very broad area of low pressure over the southern Gulf of Mexico on June 3rd. However, wind shear and dry air aloft helped to displace the majority of the convection away from the storm center which limited organization and growth. By June 5th the low moved into a more favorable environment for growth where it was upgraded to Tropical Storm Status around 1800 UTC when the center was located about 270 n mi south west of St. Petersburg, Florida. Andrea continued to strengthen as it found itself downstream of an upper level trough. This region is associated with enhanced upper level divergence allowing the cyclone to intensify until peak intensity of 55 kt winds was meet at 1200 UTC on June 6. Dry air entrainment weakened Andrea slightly before landfall was made near Steinhatchee,

Florida. Tropical Storm Andrea continued to move to the northeast through southern

Georgian and northeastern South Carolina where the cyclone eventually became extratropical eventually making its way into the Gulf of Maine were it was eventually absorbed by a stronger area of low pressure near Nova Scotia. Figure 15 shows Tropical

Storm Andrea’s track and strength.

Damage caused by Tropical Storm Andrea was minimal with most of Florida,

Georgia, and South Carolina receiving tropical storm force winds around 40 kts or less

35 with very little convection near the center of the storm. Storm surge was around 1-4 feet which produced only minor coastal flooding. Total rainfall amounts across the southeast ranged anywhere from 3-5 inches with isolated totals as high as 5-8 inches causing minor flooding. However, an isolated heavy rain event occurred on the trailing edge of the storm which produced 8-15 inches of rain in a 24 hour period causing major urban flooding in Miami and Fort Lauderdale. Andrea produced a total of 11 tornadoes mostly in Florida producing a few EF 1 tornadoes. Total damages were reported to be less than

25 million.

Although 11 tornadoes were reported to have occurred by Andrea, only 10 of those tornadoes occurred within the 24 hours before/after landfall which occurred around

2200 UTC June 6th.The initial five tornadoes were rated EF 0 except for one in Palm

Beach County which was rated EF 1. The tornadoes occurred shortly after 0600 UTC on

June 6th near Miami and Tampa, Florida. It is not surprising that an EF 1 spawned near

Miami based on how unstable the atmosphere was at the time. Figure 16 shows the 0000

UTC sounding for Miami, Florida. One can see how quickly the atmosphere begins to cool near the surface along with a very low liquid condensation level. This allowed

CAPE values to reach 2025 J/kg and the SWET value to be well above 200 indicating that severe weather is likely. While the environment seems to be conducive for potential tornadoes, did they occur under a gradient of RH as Curtis believed? Figure 17 shows the

RH values for 0600 UTC. It is clear that the atmosphere throughout Florida is extremely saturated where RH is well above 90%. However, at 700 hPa a weak RH gradient develops well off to the south. At this time RH dips from 90+% to near 65% near the

36 southern tip of the state where three of the tornadoes occurred. Not shown is the 1200

UTC sounding for Miami. The 1200 UTC sounding indicates that several dry air intrusions moved into the region sometime between 0000 and 1200 UTC. This helps confirm that the RH gradient seen over southeastern Florida was indeed there at the time.

The 0000 UTC and 1200 UTC sounding for Tampa also agrees with the reanalysis data showing an environment that remains saturated through most of the column. Any dry air that moved in was weak and was isolated to 400 hPa and higher.

The final five tornadoes including the second EF 1 spawned north of Jacksonville near the Florida/Georgia border and south of Tampa just after 1800 UTC the same day.

As the tropical system continues to move north over the Florida Panhandle the gradient begins to shift north. Unfortunately, the tropical cyclone prevented a 1200 UTC balloon launch for Jacksonville however, the 1200 UTC balloon launch for Tampa was available.

The 1200 UTC sounding seen in figure 18 shows an environment that is saturated up until about 400 hPa before some dry air begins to move through. Figure 19 depicts the

0000 UTC sounding for Tampa on June 7th. A very large dry air intrusion can be seen impacting the mid-levels from about 650 hPa to 350 hPa. Figure 20 which shows the RH values for 1800 UTC on June 6th seems to pick up on the dry air intrusion moving through. According to the reanalysis data 6 hours after the 1200 UTC balloon launch on

June 6th the environment remains saturated at 300 and 700 hPa while there is a very strong RH gradient over western Florida at 400 hPa with a slightly weaker RH gradient at

500 hPa. The three tornadoes that spawned south of Tampa 400 hPa occurred under a region where the RH dips from 60% to 20%. At 500 hPa the RH gradient increases from

40-60% over the same area. Without a special 1800 UTC sounding it is difficult to determine the position and exactly how strong the gradient was with more accuracy.

However, the observed soundings do verify that an RH gradient did move through that may have affected at least three of the five tornadoes that occurred during this outbreak.

Figure 15. Best track positions for Tropical Storm Andrea, 5-7 June 2013.

Figure 16. Atmospheric profile sounding for Miami, Florida taken at 0000 UTC on June 6. Image was taken from the University of Wyoming Department of Atmospheric Science sounding page.

Figure 17. Relative humidity for 300, 400, 500, and 700 hPa for 0600 UTC on 6 June. Images created using the European Centre for Medium-Range Weather Forecasts ERA- Interim reanalysis data within Matlab. Warmer colors indicate dry air while cooler colors indicate moist air. Black star indicates the location of the tropical cyclone at the current time. Dots represent the location of the various tornadoes that spawned at that time.

Figure 18. Atmospheric profile sounding for Tampa, Florida taken at 1200 UTC on June 6. Image was taken from the University of Wyoming Department of Atmospheric Science sounding page.

Figure 19. Atmospheric profile sounding for Tampa, Florida taken at 0000 UTC on June 7. Image was taken from the University of Wyoming Department of Atmospheric Science sounding page.

Figure 20. Relative humidity for 300, 400, 500, and 700 hPa for 1800 UTC on 16 June. Images created using the European Centre for Medium-Range Weather Forecasts ERA- Interim reanalysis data within Matlab. Warmer colors indicate dry air while cooler colors indicate moist air. Black star indicates the location of the tropical cyclone at the current time. Dots represent the location of the various tornadoes that spawned at that time.

3.4 Bill (2003)

On June 28th a tropical wave interacted with an upper level low which created the low pressure that would eventually become Tropical Storm Bill over the Yucatan

Peninsula. Although wind shear was favorable for development friction from the land prevented any tropical storm growth. Convection became much better organized when the system moved off shore where it was upgraded to a tropical depression by 0600 UTC on the 29th of June. The system was later upgraded to tropical storm status a few hours later. Tropical Storm Bill continued to strengthen as the system continued to move to the north-northwest as shear decreased and it interacted with the warmer Gulf of Mexico waters. The system then shifted towards the northeast where its peak intensity of 50 kt winds and a pressure of 997 hPa were recorded on June 30th. Tropical Storm Bill made landfall near King Lake, Louisiana where it quickly began to weaken as it moved through

Mississippi and Alabama. Figure 21 shows the track and strength of Tropical Storm Bill.

The damage associated with bill was minor with wind damage knocking down tree branches resulting in power outages coastal Mississippi and Louisiana. The worst storm surge was confined to Terrebone Parish were a local levee failed resulting in nearby homes to be flooded. A total of eight tornadoes were associated with bill including an EF 1 that hit a private school before going on to hit a mobile home park damaging at least 20 homes. The total estimated damages across Louisiana and

Mississippi was around 50 million.

Tropical Storm Bill produced a total of eight tornadoes during the 24 hour period before and after landfall. The first initial three tornadoes spawned around 1800 UTC on

June 30th in extreme southeastern Louisiana. The vertical profile taken for LIX at 1200

UTC shown in figure 22 indicates that the entire column is saturated with no clear dry air intrusion at any level. This is also what is shown using the reanalysis data. Figure 23 shows the RH values at 1800 UTC on June 30th. Using this information alongside the RH plots in figure 23 we can see that the RH gradient is displaced further west of where the tornadoes spawned. 300 hPa and 500hPa have a strong gradient west of the tornado locations with RH dropping from 90% to 40% towards the middle of Louisiana. As a result none of the tornadoes in the first outbreak occurred under an RH gradient.

The remaining five tornadoes that spawned in Alabama, Georgia, and Mississippi all occurred shortly after 0000 UTC on July 1st. The Birmingham, Alabama (not shown) and the Tallahassee, Florida soundings were as they were the closest launch sites to the remaining tornadoes. Both TLH and BMX indicate the levels below 600 hPa are dry while above 600hPa remained relatively saturated. Figure 24 shows RH for 0000 UTC on

July 1st. The plots reveal that there does not seem to be any identifiable strong RH gradient over the tornado outbreak region. There does seem to be a pocket of drier air over the southeast at 700hPa indicating that the sounding matches the reanalysis data fairly well. At this time four out of the five tornadoes occur in a region where RH dips below 80% however, there does not seem to be a strong RH gradient present. The environment seems to be dominated by a larger drier air mass rather than pockets of drier air advecting into the region.

Figure 21. Best track positions for Tropical Storm Bill, 29 June- 2 July, 2003. Track after landfall is based on analyses from the NOAA Hydrometeorological Prediction Center

Figure 22. Atmospheric profile sounding for Slidell Muni, Louisiana taken at 1200 UTC on June 30. Image was taken from the University of Wyoming Department of Atmospheric Science sounding page.

Figure 23. Relative humidity for 300, 400, 500, and 700 hPa for 1800 UTC on 30 June. Images created using the European Centre for Medium-Range Weather Forecasts ERA- Interim reanalysis data within Matlab. Warmer colors indicate dry air while cooler colors indicate moist air. Black star indicates the location of the tropical cyclone at the current time. Dots represent the location of the various tornadoes that spawned at that time.

Figure 24. Relative humidity for 300, 400, 500, and 700 hPa for 0000 UTC on 1 July. Images created using the European Centre for Medium-Range Weather Forecasts ERA- Interim reanalysis data within Matlab. Warmer colors indicate dry air while cooler colors indicate moist air. Black star indicates the location of the tropical cyclone at the current time. Dots represent the location of the various tornadoes that spawned at that time.

Figure 25. Atmospheric profile sounding for Tallahassee, Florida taken at 0000 UTC on July 1. Image was taken from the University of Wyoming Department of Atmospheric Science sounding page.

3.5 Bonnie (2004)

Tropical Storm Bonnie originally developed from a tropical wave that moved off the coast of Africa and moved westward across the Atlantic. The already well defined rotation began to develop convective bands where it was upgraded to a tropical depression by 1200 UTC on August 3rd. Once the system reached the eastern Caribbean

Sea the surface circulation was lost as well as the convective bands. Once the system reached the western Caribbean Sea it quickly redeveloped and formed a new circulation allowing it to regain its tropical depression status. The system continued to quickly track west-northwest where it strengthens further off the tip of the Yucatan Peninsula becoming a Tropical Storm. By 1800 UTC on August 11th Bonnie had reached a peak intensity of 55 kts winds and a minimum pressure of 1001 hPa. Bonnie weakened due to wind shear shortly before landfall near Saint Vincent and Saint George Islands south of

Apalachicola Florida. The tropical storm continued to move to the northeast where its remnants were last tracked just south of Cape Cod, Massachusetts. Tropical Storm

Bonnies track and intensity are shown in figure 26.

Bonnie produced a tornado outbreak across the southeastern United States. A total of 18 tornadoes between the 24 hours before and after landfall were recorded across

Florida, South Carolina, and North Carolina. The vast majority of the tornadoes all occurred around 1800 UTC on August 12th. The 1800 UTC vertical profiles for

Jacksonville, Florida and Charleston, South Carolina were used as they were the two sites closes to the tornado outbreaks and were under an RH gradient at the time. Figure 27 shows the 1800 UTC sounding for Jacksonville, Florida. Figure 28 shows the sounding

52 for Charleston, South Carolina taken at the same time. One can see that both sounding locations pick up on dry air layers in the upper atmosphere between 500 and 700 hPa.

Figure 29 shows the RH values for 1800 UTC on August 12th. We can see that the tornado outbreak was spread out across the southeast. A lack of a special 1800 UTC sounding for Greensboro or Newport, North Carolina makes it difficult to determine to what extent the RH gradient stretched north or west past Charleston. However, the soundings do confirm that the RH gradient seen along the coast in figure 29 was there. At

300hPa there is a narrow band of dry air over the southern tip of Florida over a region where three tornadoes spawned. The three tornadoes occurred under a region where the

RH ranges from 30-50% however, the strong RH gradient is located to far north for the southern Florida tornadoes and to far south for the northern Florida and South/North

Carolina tornadoes. By 400 hPa the dry air over Florida deepens pushing the RH gradient further north placing five tornadoes on the edge of the steep RH gradient aloft. At 500 hPa the RH gradient is placed directly over the northern Florida and South Carolina tornadoes supporting Curtis theory.

The last four tornadoes occurred along the North Carolina coast northeast of the storm center just after 0600 UTC on August 13th. There was no 0600 UTC sounding available for Newport, North Carolina however, the 0000 UTC and 1200 UTC soundings

(not shown) indicates that the environment remained fairly saturated throughout the column with scattered pockets of dry air. This is what is seen in the RH images for 0600

UTC along the North Carolina coast seen in figure 30. At 300 and 400 hPa the RH is well above 80% along the coast. It is not until 500 and 700 hPa that we start to see the column

53 become less saturated. There does seem to be evident of a very weak RH gradient at these two levels were the values for RH range from 60-80% however, the gradient itself is not steep. A much steeper gradient in RH can be seen well off towards the northwest.

Figure 26. Best track positions for Bonnie, 3-13 August, 2004. Track after landfall stage is based on analyses from the NOAA Hydrometeorological Prediction Center (HPC).

Figure 27. Atmospheric profile sounding for Jacksonville, Florida taken at 1800 UTC on Aug 12. Image was taken from the University of Wyoming Department of Atmospheric Science sounding page.

Figure 28. Atmospheric profile sounding for Charleston, South Carolina taken at 1800 UTC on Aug 12. Image was taken from the University of Wyoming Department of Atmospheric Science sounding page.

Figure 29. Relative humidity for 300, 400, 500, and 700 hPa for 1800 UTC on 12 Aug. Images created using the European Centre for Medium-Range Weather Forecasts ERA- Interim reanalysis data within Matlab. Warmer colors indicate dry air while cooler colors indicate moist air. Black star indicates the location of the tropical cyclone at the current time. Dots represent the location of the various tornadoes that spawned at that time.

Figure 30. Relative humidity for 300, 400, 500, and 700 hPa for 0600 UTC on 13 Aug. Images created using the European Centre for Medium-Range Weather Forecasts ERA- Interim reanalysis data within Matlab. Warmer colors indicate dry air while cooler colors indicate moist air. Black star indicates the location of the tropical cyclone at the current time. Dots represent the location of the various tornadoes that spawned at that time.

3.6 Charley (2004)

Charley was characterized as the strongest hurricane to hit the United States since

Hurricane Andrew back in 1992. Although Charley was not a large storm it’s destruction was felt not only along the coast but inland as well. The energy associated with Charley was first tracked as a tropical wave moving off the coast of Africa. As the system moved rapidly west at 20-24 kts convection began to form eventually becoming a tropical depression by 1200 UTC on August 9th and becoming Tropical Storm Charley a day later.

Charley continued to strengthen until it reached hurricane status near Jamaica on August

11th. Charley movement slowed down quite a bit as it shifted towards the northwest.

Charley’s slow movement in an environment favorable for intensification prompted the tropical cyclone to deepen until it reached Category 2 status around 1500 UTC on August

12th. Surface observations in Cuba indicate that Charley strengthen more just before landfall on the island with maximum winds of 105 kts were recorded. By the time

Charley had passed through Cuba it came in contact with a deep trough which helped quickly shift Charley’s track to the northeast where it set aim for the Florida coast. Rapid intensification occurred as Charley’s eye shrunk in size resulting in an increase of winds speeds of up to 125 kts prompting officials to upgrade Charley to a Category 4 storm.

Hurricane Charley made landfall as a Category 4 hurricane near Cayo Costa, Florida around 2000 UTC 13 August with maximum sustained winds of 130 kts. The incredible strength of the winds associated with the eyewall devastated coastal communities. Once over land Hurricane Charley began to weaken however, not before leaving a path of destruction across the state of Florida. Hurricane Charley would eventually go on to make

60 landfall as a much weaker storm in Cape Romain, South Carolina and later in North

Myrtle Beach, South Carolina. Figure 31 shows Hurricane Charley’s track and intensity.

The total estimate in damages as a result of Charley was reported to be around 6.5 billion dollars. The devastating wind speed experienced through much of the state resulted in homes being damaged and wide spread power outages. Rainfall as high as 5 inches was recorded over Florida with locally heavier amounts of 6-8 inches.

North/South Carolina also experienced rainfall amounts ranging from 5-7 inches. The

Storm Predictions Center National Severe Weather Database indicates there were 18 tornadoes that touched down associated with Hurricane Charley. The most destructive tornado was located just south of Daytona Beach on August 13th where an EF 1 produced a quarter of a mile long track of damage. Another EF 1 tornado formed on August 14th near Kitty Hawk, North Carolina which luckily was less destructive. There were two sets of tornado events with the first occurring over Florida and the second over North

Carolina.

The first 10 tornadoes occurred across Florida around 1800 UTC on August 13,

2004. The tornadoes spawned towards the southeast of Tampa while the center of rotation was located just off the coast near Fort Myers. Observed soundings for Tampa and Miami at 1800 UTC the same day were used to analyze the atmosphere and compare it to the reanalysis data. Based on the sounding for Tampa (figure 33) the environment is saturated through the entire column with a dry air intrusion below 700 hPa towards the surface. The sounding over Miami (figure 34) indicates that the environment is not as saturated as Tampa with multiple pockets of dry air being sampled especially at 700 and

300 hPa. Based on the sounding data a gradient in RH should be present. Figure 32 shows the RH values for 1800 UTC across Florida. By 1800 UTC the center of rotation has moved just off the coast of Florida and as a result saturating much of the environment over central Florida. At 500 hPa and above the majority of the state has RH values greater than 80% which slowly drops off towards the southeast. A small weak gradient is seen at 300 hPa near the southern tip of Florida. Any steep gradient in RH is located well offshore away from the outbreak region. A drastic gradient in RH does not become present until 700 hPa. At this time the gradient in RH between Tampa and Miami drops from 90% to 30%. Figure 32 also indicates that more than half of the tornadoes spawned under the gradient located west of Tampa agreeing with the findings by Curtis. The tornadoes spawned were the gradient dip between 90% and 50%. The observed 1800

UTC soundings for both Tampa (figure 33) and Miami (figure 34) indicates that the reanalysis data for this day is accurate. Hurricane Charley was one of the first examples where the tornado outbreak region as well as the steep RH gradient aloft was collocated only at 700 hPa.

The final group of tornadoes just after 1800 UTC on August 14 in North Carolina.

A total of five tornadoes occurred at this time. The 1800 UTC atmospheric sounding for

New Port, North Carolina was used due to its proximity to the outbreak region. Based on the vertical profile the environment there are multiple small dry air intrusions with the largest pockets of dry air being found at both 400 and 300 hPa. Figure 35 shows the RH over North Carolina for 1800 UTC on the 14th. At 500 hPa and 700 hPa the environment over were the tornadoes occurred is saturated with RH values higher than 85%. There is a

62 steep RH gradient present at these levels but they are far removed to the east and west of the outbreak region. By 400 hPa the gradient pushed towards the outbreak region from both the east and west. While the RH gradient to the east is steeper it is located too far off shore to impact the tornado outbreak region. The gradient to the west while not as steep indicates that there is a strong layer of dry air moving in. RH values drop form 90% at the coast to 30% further inland. Even with the steep gradient only two of the tornadoes occur under the gradient. The other three occur along the coast where RH values are

90%+. By 300 hPa the gradient to the west decreases substantially. The two tornadoes that were under the RH gradient at 400 hPa are no longer under a gradient. The reanalysis data fails to pick up on the dry layer at 400 hPa which is seen in the observed sounding for Newport (figure 36). As a result the gradient well off shore in the reanalysis image may have been further west possibly incorporating some of the tornadoes along the coast similar to what is seen at 300 hPa. Overall the steep gradients in RH that were present were not located over the outbreak region.

Figure 31. Best track positions for Hurricane Charley, 9-14 August 2004.

Figure 32. Relative humidity for 300, 400, 500, and 700 hPa for 1800 UTC on 13 Aug. Images created using the European Centre for Medium-Range Weather Forecasts ERA- Interim reanalysis data within Matlab. Warmer colors indicate dry air while cooler colors indicate moist air. Black star indicates the location of the tropical cyclone at the current time. Dots represent the location of the various tornadoes that spawned at that time.

Figure 33. Atmospheric profile sounding for Tampa, Florida taken at 1800 UTC on Aug 13. Image was taken from the University of Wyoming Department of Atmospheric Science sounding page.

Figure 34. Atmospheric profile sounding for Miami, Florida taken at 1800 UTC on Aug 13. Image was taken from the University of Wyoming Department of Atmospheric Science sounding page.

Figure 35. Relative humidity for 300, 400, 500, and 700 hPa for 1800 UTC on 14 Aug. Images created using the European Centre for Medium-Range Weather Forecasts ERA- Interim reanalysis data within Matlab. Warmer colors indicate dry air while cooler colors indicate moist air. Black star indicates the location of the tropical cyclone at the current time. Dots represent the location of the various tornadoes that spawned at that time.

Figure 36. Atmospheric profile sounding for Newport, North Carolina taken at 1800 UTC on Aug 14. Image was taken from the University of Wyoming Department of Atmospheric Science sounding page.

3.7 Cindy (2005)

Hurricane Cindy originally formed from a tropical wave that originated off the coast of Africa. Very little convection was associated with the tropical wave as it moved across the Atlantic. The tropical wave eventually split with the southern portion continuing west while the northern portion which had active convection turned more to the northwest. U.S. Air Force Reserve reconnaissance confirmed that a tropical depression had formed around 1800 UTC about 70 n mi east of Chetumal, Mexico. The tropical depression quickly moved through the Yucatan Peninsula were it came in contact with a upper level trough causing the system to pick up speed as well as deepen into a tropical storm around 0600 UTC on July 5th. Weak vertical wind shear allowed Tropical

Storm Cindy to strengthened becoming a Hurricane less than 24 hrs later. Cindy was able to maintain hurricane strength long enough until it made landfall near Grand Isle,

Louisiana at 0300 UTC on July 6th becoming the first U.S. landfall in what turned to be a very active Atlantic Basin hurricane season. Cindy quickly weakened into a tropical storm before making a second landfall near Waveland, Mississippi. Cindy continued to weaken as it moved across the southeast United States until it merged with a stationary front becoming extratropical. Figure 37 shows Hurricane Cindy’s track and intensity.

Cindy’s damaging winds caused considerable damage to trees and buildings especially across southeastern Louisiana. More than 250,000 customers lost power as a result of downed power lines. Cindy produced storm surge as high as 4-6 feet along coastal Louisiana. 3-4 ft storm surge was reported in Alabama while 2-3 foot storm surge was recorded as far as the Florida panhandle. Total rainfall amounts were on average 4-6

70 inches across Louisiana, Mississippi, and Alabama with locally heavier amounts around

7-9 inches causing widespread flooding causing some major road ways to close for a few hours. A total of 33 tornadoes were confirmed many occurring after Cindy had moved inland. While most tornadoes were weak there was one EF 2 tornado that formed in

Georgia. Overall the wide spread tornado outbreak caused considerable damage to both homes and business. In total Hurricane Cindy caused a reported 320 million in damages.

Out of the 33 confirmed tornadoes to have touched down as a result of Hurricane

Cindy only 24 occurred during the 24 hrs before or after landfall. The outbreak was located mainly across Alabama and Georgia. The first set of tornadoes occurred in the early morning of July 6th after 0600 UTC in Alabama. No 0600 UTC sounding for

Birmingham was available so the sounding for 0000 UTC (not shown) and 1200 UTC

(not shown) were used to analyze the environment leading up to the outbreak. Based on the 0000 UTC soundings while the lower atmosphere remained saturated from 500 to 700 hPa the upper atmosphere up until 300 hPa had multiple large pockets of dry air over the region. By 1200 UTC the atmosphere above 700 hPa became completely saturated indicating that moist air was being advected into the region rather than dry air. The observed vertical profile for Tallahassee at 0000 UTC on July 6 shows an extremely dry environment from the surface all the way up to 300 hPa (figure7c). The 1200 UTC sounding for Tallahassee as seen in figure 40 indicates that the large dry intrusion began to erode as the tropical cyclone center moved northeast closer to Tallahassee. There were still two dry slots present at 700 and 400 hPa. This indicates that there was much drier air present but located further off to the east. As a result there must be an RH gradient

71 located between Birmingham and Tallahassee. Figure 38 shows the RH values for 0600

UTC the same day to determine if the for mentioned RH gradient occurred over the outbreak region. The tornadoes were confined to southern Alabama with the center of the tropical system located over Louisiana. At 300 hPa any gradient in RH is located well off to the southwest and to the southeast of the outbreak region. All the tornadoes also occurred under a region where the RH was 90%. At 400 hPa the gradient to the west and east push towards the outbreak region. The larger RH gradient to the west continues to remain too far west to impact the outbreak region. The weaker gradient to the east is able to move far enough west that two tornadoes fall under the gradient but the majority of the storms still occurred when the RH was 80%. At 500 hPa the environment becomes saturated pushing the gradients in RH away from the outbreak region. At 700 hPa the environment becomes drier allowing the gradient to the east to push west however, the steep gradient is located over eastern Alabama incorporating only two tornadoes once again.

The next 11 tornadoes occurred over central Alabama near the border with

Georgia after 1800 UTC on July 6th. The 1200 UTC sounding for Birmingham (not shown) indicates that the entire column is relatively saturated with the driest levels being located below 700 hPa. Figure 41 shows the RH values for 1800 UTC the same day. The tornadoes were located in the right front quadrant of the storm. The RH at 300 hPa remains saturated over the outbreak region with the steep gradient located near the Gulf

Coast. At both 400 hPa and 500 hPa a weak gradient pushed northwest and incorporates eight of the 11 tornadoes that spawned during this time. At 400 hPa eight of the tornadoes

72 occur where the RH is between 70-80% however, the majority of the tornadoes our located on the outer edge of the weak gradient. At 500 hPa the gradient becomes steeper where again the tornadoes developed under a region where the RH increases from 60-

85%. The environment becomes much more saturated by 700 hPa weakening the gradient seen in the upper levels. As a result only four tornadoes occur under a very weak gradient in RH to the east. The RH gradient at 500 did the best at pinpointing where the tornadoes might be located. The observed soundings for Birmingham and Peach Tree City (not shown) show that the atmosphere does become drier with decreasing RH values as you moved east similar to what is depicted in the reanalysis data.

The final batch of tornadoes occurred over western Georgia just after 0000 UTC on July 7th. An incomplete sounding for Peach Tree City was taken that day only profiling the lower half of the troposphere and as a result was not included in the analysis. Figure 42 shows the RH values for 0000 UTC. Again the tornadoes occurred in the right front quadrant of the storm. At 700 hPa the environment is saturated throughout the region. At 500 hPa a RH gradient to the south begins to move through. At this time the center of the system is located under a moderate gradient however, the tornadoes located to the northeast are on the outer fringes of the gradient. The RH gradient at 400 hPa becomes steeper especially over the cyclones center of rotation. Out of all the levels this is the level where the tornadoes are located under the driest layer where RH dips to about 65-70%. However, the tornadoes are located in a weaker section of the RH gradient. At 300 hPa the RH gradient retreats back to the south placing the tornadoes in a more saturated environment once again. Unfortunately, the incomplete sounding makes

73 it difficult to compare the results from the reanalysis data to what was observed at the time. Overall these tornadoes occurred near a steep RH gradient especially at 400 hPa however, the steepest portion of the gradient was still located too far to the south.

Figure 37. Best track positions for Hurricane Cindy, 3-7 July 2005. Track during the extratropical stage is based on analyses from the NOAA Hydrometeorological Prediction Center.

Figure 38. Relative humidity for 300, 400, 500, and 700 hPa for 0600 UTC on July 6th. Images created using the European Centre for Medium-Range Weather Forecasts ERA- Interim reanalysis data within Matlab. Warmer colors indicate dry air while cooler colors indicate moist air. Black star indicates the location of the tropical cyclone at the current time. Dots represent the location of the various tornadoes that spawned at that time.

Figure 39. Atmospheric profile sounding for Tallahassee, Florida taken at 0000 UTC on July 06. Image was taken from the University of Wyoming Department of Atmospheric Science sounding page.

Figure 40. Atmospheric profile sounding for Tallahassee, Florida taken at 1200 UTC on July 06. Image was taken from the University of Wyoming Department of Atmospheric Science sounding page.

Figure 41. Relative humidity for 300, 400, 500, and 700 hPa for 1800 UTC on July 6th. Images created using the European Centre for Medium-Range Weather Forecasts ERA- Interim reanalysis data within Matlab. Warmer colors indicate dry air while cooler colors indicate moist air. Black star indicates the location of the tropical cyclone at the current time. Dots represent the location of the various tornadoes that spawned at that time.

Figure 42. Relative humidity for 300, 400, 500, and 700 hPa for 0000 UTC on July 7th. Images created using the European Centre for Medium-Range Weather Forecasts ERA- Interim reanalysis data within Matlab. Warmer colors indicate dry air while cooler colors indicate moist air. Black star indicates the location of the tropical cyclone at the current time. Dots represent the location of the various tornadoes that spawned at that time.

3.8 Dolly (2008)

Hurricane Dolly originated as a tropical wave off the coast of Africa that quickly began to move across the Atlantic. By the time the system reached the Caribbean Sea it was producing deep convection and tropical storm force winds however, no clear center of circulation was found. The system was then upgraded to tropical storm status on July

20th when a well-defined circulation was found. Tracking Tropical Storm Dolly proved difficult for forecasters to track because the system soon began to disorganize as it pass just north east of the Yucatan Peninsula. Once in the Gulf of Mexico the cyclone quickly reorganized and was steered to the west by a large high pressure system siting over the

U.S. By 0000 UTC on July 23 Tropical Storm Dolly was upgraded to a hurricane.

Hurricane Dolly reached peak intensity as a Category 2 storm with winds of 85 kts just

20 n mi east of the Texas/Mexico border. Cooler sea surface temperatures as well as dry air from Mexico entraining into the storm are credited with weakening Dolly shortly before landfall. Hurricane Dolly eventually made landfall as a Category 1 storm near

South Padre Island, Texas around 1800 UTC on the 23 of July. Hurricane Dolly’s track can be seen in figure 43.

Strong winds damaged roofs, weak structures, downed trees, and caused widespread power outages. Heavy rain across the Rio Grande Valley was reported as a result of Hurricane Dolly’s slow track across the region. Major inland flooding occurred as many areas reported rainfall totals as high as 10 inches. Some locally heavier amounts were reported as high as 15 inches. Storm surge was recorded as high as 4 feet along the

Texas coastline. Six tornadoes were reported to have touched down as a result of Dolly.

Fortunately, all were EF 0 in strength and caused very little if any damage across Texas.

A total of 1 billion dollars in damages were reported as a result of Hurricane Dolly.

Hurricane Dolly produced a total of six tornadoes across southern Texas after

1800 UTC on July 23rd. Atmospheric soundings for Corpus Christi, Texas were used due to its proximity to the six tornadoes. Based on the sounding the atmosphere becomes substantially drier above 300 hPa. Figure 44 shows the RH values for southern Texas at

1800 UTC on July 23rd. At 300 hPa all six tornadoes occur under a region where the RH values are well above 80%. This contradicts what the observed sounding indicates seen in figure 45. The reanalysis data is failing to pick up on the dry air in the upper levels or more likely is that the sounding is sampling the much drier air that is located further north evident by the much steeper gradient in RH to the north and to the southeast. By 400 hPa the two dry intrusion progress closer to the outbreak region. At this time four of the six tornadoes are located under a region where the RH is between 45-60%. The remaining two towards the south occurred where RH was 80% or higher. By 500 hPa both RH gradients begin to erode. The RH gradient to the southeast weakens substantially with RH values climbing to about 70%. The RH values of 45-60% seen at 400 hPa can be seen retreating out into the Gulf of Mexico. The RH gradient to the north remains in place however the contour lines can be seen separating suggesting a weakening gradient. As a result of the weakening gradient only the two northern most tornadoes occurred near a

RH gradient aloft at 500hPa. Closer to the surface at 700 hPa the reanalysis data seems to agree with the observed sounding (figure 45) data indicating that much of southern Texas

82 is saturated. Overall only four tornadoes occurred just south of where the tightest gradient in RH was located.

Figure 43. Best track positions for Hurricane Dolly, 20-25 July 2008. Track during the inland tropical depression stage is based partially on analyses from the NOAA Hydrometeorological Prediction Center

Figure 44. Relative humidity for 300, 400, 500, and 700 hPa for 1800 UTC on 23 July. Images created using the European Centre for Medium-Range Weather Forecasts ERA- Interim reanalysis data within Matlab. Warmer colors indicate dry air while cooler colors indicate moist air. Black star indicates the location of the tropical cyclone at the current time. Dots represent the location of the various tornadoes that spawned at that time.

Figure 45. Atmospheric profile sounding for Corpus Christi, Texas taken at 1800 UTC on July 23. Image was taken from the University of Wyoming Department of Atmospheric Science sounding page.

3.9 Fay (2002)

Fay originally developed from a weak low pressure system traveling along an upper level trough stationed over the northern Gulf of Mexico. The low began to intensify and develop deep convection as it moved over the warm waters with seas surface temperatures over 30*C. An Air Force Reconnaissance flight was able to identify a closed circulation as well as strong enough winds to prompt NHC to upgrade the system to a tropical depression by 1800 UTC on September 5th. The depression continued to move to the south-southwest were it continued to intensify until it was upgraded to tropical storm status. Tropical Storm Fay reached peak intensity 125 n mi southeast of

Galveston when winds reached 50 kts. Fay retained its strength until landfall was made just east of Port O’Connor, Texas. The cyclone quickly began to dissipate but not before leaving behind an enormous amount of rainfall. Tropical Storm Fays track and intensity can be seen in figure 46.

Due to Tropical Fay’s relatively weak strength at landfall damage was kept to a minimum. Storm surge values remained under 3 feet across much of Texas and western

Louisiana causing minor beach erosion and coastal road flooding. Fay produced a tremendous amount of rainfall throughout Texas. San Antonio received anywhere from 4-

8 inches of rain while other locations reported rainfall amounts as high as 9-12 inches which caused widespread flooding. A total of twelve tornadoes were associated with

Tropical Storm Fay. However, only nine of the twelve tornadoes touched down with in the 24 hrs before or after landfall. The tornadoes were also isolated towards the coast.

The first five tornadoes occurred shortly after 0000 UTC on September 7th. The tornadoes were centered near the Greater Houston area as seen in figure 47. Figure 47 also depicts the RH values for southern Texas just before the tornadoes occurred. One can clearly see right away that there are large areas of very dry air (RH<25%) being entrained into the storm from the higher elevations of the Mexican plateau off to the west.

Since the cyclone was moving due west at the time one can see the counter clock wise rotation of the cyclone wrapping high RH air to the north while also funneling low RH air to the south. Tropical Storm Fay was the first tropical cyclone analyzed that had such a large dry air intrusion present at the time the tornadoes occurred. Another interesting observation is that the strong RH gradient present shifts further south as you move down the atmosphere. For example, at 300 hPa all five tornadoes occur directly under the region where the tightest RH gradient is located. However, at 400 hPa the same gradient pushes south leaving the tornadoes under a region where the RH is between 65-80% near the northern edge of the gradient. At 500 hPa the gradient weakens while moist air from the Gulf of Mexico continues to advect into the region. At this time the tornadoes have spawned when the RH is near 90%. At 700 hPa much of the Texas coastline is completely saturated with RH values where the tornadoes are located near 100%. The observed 0000 UTC sounding for Corpus Christi (figure 48) showed a similar atmospheric profile seen in the reanalysis data with the driest air located at 300 hPa gradually becoming more saturated as you approach 700 hPa. This allows for a more confident statement in which the gradient at 300 hPa did an accurate job at predicting the location of the first five tornadoes associated with Tropical Storm Fay.

The final four tornadoes occurred after 0600 UTC on September 8th on the back side of the cyclone after moving well inland. The observed 0000 UTC sounding for

Corpus Christi on the same day can be seen in figure 49. The atmospheric profile at the time shows a large dry air intrusion above 500 hPa with a much smaller layer of dry air near the surface and around 700 hPa. Figure 50 presents the RH values for 0600 UTC just before the tornadoes spawned. Right away one can see that the reanalysis data did an accurate job of matching what was observed based on the sounding. At 300 hPa the four tornadoes occurred under an extremely dry region with RH values well below 20%.

However, the RH gradient is located to far west near the center of the tropical cyclone. At

400 hPa the gradient shifts east incorporating the tornadoes under a RH gradient between

20-40% however, the strongest section of the gradient is just off to the west. At 500 hPa the RH gradient weakens but the tornadoes are located under a wider gradient in RH ranging from 40-70%. This is similar to what was seen with the first set of tornadoes at

300 hPa mentioned above but with a weaker RH gradient. By 700 hPa any residual dry air has been completely eroded leaving the majority of the area saturated with RH values above 80% where the tornadoes were located.

Figure 46. Best track positions for Tropical Storm Fay, 5-11 September 2002, with minimum central pressure.

Figure 47. Relative humidity for 300, 400, 500, and 700 hPa for 0000 UTC on 7 September. Images created using the European Centre for Medium-Range Weather Forecasts ERA-Interim reanalysis data within Matlab. Warmer colors indicate dry air while cooler colors indicate moist air. Black star indicates the location of the tropical cyclone at the current time. Dots represent the location of the various tornadoes that spawned at that time.

Figure 48. Atmospheric profile sounding for Corpus Christi, Texas taken at 0000 UTC on September 7. Image was taken from the University of Wyoming Department of Atmospheric Science sounding page.

Figure 49. Atmospheric profile sounding for Corpus Christi, Texas taken at 0000 UTC on September 8. Image was taken from the University of Wyoming Department of Atmospheric Science sounding page.

Figure 50. Relative humidity for 300, 400, 500, and 700 hPa for 0600 UTC on 8 September. Images created using the European Centre for Medium-Range Weather Forecasts ERA-Interim reanalysis data within Matlab. Warmer colors indicate dry air while cooler colors indicate moist air. Black star indicates the location of the tropical cyclone at the current time. Dots represent the location of the various tornadoes that spawned at that time.

3.10 Fay (2008)

Tropical Storm Fay originated from a tropical wave that emerged off the coast of

Africa before quickly moving westward across the Atlantic Ocean. The system eventually slowed down to about 10-15 kts which helped increase the amount of convection associated with the system. The system was upgraded to a tropical depression shorty after passing Puerto Rico at 1200 UTC on August 15th. A large ridge helped steer the system to the west making landfall near El Cabo, Dominican Republic. Despite the mountainous terrain over Hispaniola the cyclone continued to strengthen and was upgraded to a tropical storm as the system continued to move west making landfalls in Haiti and Cuba.

Further strengthening was prevented due to increased wind shear and dry air as Tropical

Storm approached the Florida Keys. The cyclone made the first of what would be a record four landfalls over Florida at 2030 UTC near Key West Florida on August 18. The warm waters by the Keys helped the system organize developing a well-defined eye right before making its second landfall near Cape Romano, Florida on August 19. Fay increased slightly in strength even while over land until a peak intensity of 60 kts was recorded. Fay eventually reached the Atlantic were it weakened however, NHC notes that the speed of the system slowed to almost a standstill which causes wide spread major flooding along the eastern coast of the peninsula. Fay made its third landfall near Flagler

Beach before moving into the Gulf where it eventually made its final landfall over the

Florida. Tropical Storm Fays track and intensity can be found in figure 51.

A tremendous amount of rainfall fell over Florida as a result of Fay. While most places received more than 10 inches of rain Brevard County was just one of many reports

95 of more than 20 inches when Fay stalled over the eastern coast of the peninsula. Flooding resulted in more the 15,000 homes being damaged. However, a majority of the rainfall fell in rural unpopulated portions of southern Florida which helped minimize damages. In fact, the large amount of rainfall was credited with refilling reservoirs and other water sources across Florida. Storm surge damage was kept to a minimum as moderate beach erosion and some coastal flooding was reported as a result of storm surge heights around

2-4 feet. Tropical Storm Fay was one of the most active cyclones in terms of tornado production. NHC reported a total of 81 tornadoes across five states. While the majority of the tornadoes were EF 0 in strength a few made it to EF 2 strength. On EF 2 tornado alone caused 1.25 million dollars in damages in western Palm Beach County. The majority of the tornadoes spawned well after the system moved inland. Only 12 tornadoes were produced during landfall. Seven tornadoes were produced during the systems second landfall while another five spawned during the third landfall. For the purpose of this paper only these initial 12 were included. Tropical Storm Fay caused an estimated

560 million in damages.

Out of the initial seven tornadoes spawned during the first landfall four occurred just after 1800 UTC on August 18th cross the southern tip of Florida. The 1800 UTC soundings for Key West and Miami were used to calculate dew point depression values.

The 700, 500, 400, and 300 hPa dew point depression for Key West were 2.3°C, 7°C,

8°C and 8°C respectively. The dew point depression for Miami for the same levels and time were 0.1°C, 3.1°C, 6°C, and 12°C. Both soundings (not shown) indicate that while the air was saturated closer to the surface dry air intrusions were found especially above

500 hPa at both locations. Figure 52 represents the RH values for 1800 UTC across southern Florida using the reanalysis data. The reanalysis data does seem to pick up the dry air off to the north and south of the sounding launch sites matching what was observed. However, across all four levels one can see that all four tornadoes occurred under regions were the RH values were well above 80%. At 500 hPa and 700 hPa there is no RH gradient present at all near southern Florida while at 300 hPa and 400 hPa a strong gradient can be seen to the north and south yet they are too far removed. It is possible for the southernmost gradient to have shifted north after 1800Z in which it would have incorporated at least the two tornadoes across the Florida Keys.

The final three tornadoes associated with the first landfall spawned around 1200

UTC on August 19th just north of Miami, Florida. The 1200 UTC observed sounding for

Miami (figure 53) looks very similar to the soundings associated with the first four tornadoes. The environment around Miami is very saturated near the surface with very small pockets of dry air above 500hPa. The sounding is most likely sampling the dry air located north of Miami away from the tornado region seen in the reanalysis data in figure

54. The scenario for these three tornadoes is exactly the same as the one mentioned above. Across all four levels the tornadoes occurred under a region where the RH value is near 90%. Once again there is a very strong RH gradient present to the north, west, and south. However, the strongest portions of the gradients were too far removed failing to pinpoint the location of the outbreak.

The final 5 tornadoes occurred shortly after 1800 UTC on August 22nd near

Jacksonville, Florida. The 1200 UTC sounding (figure 55) indicates that the environment

97 is fairly saturated in the lower levels with a small pocket of dry air at 300 hPa where the dew point depression was 8°C. The reanalysis data did an excellent job of matching the observed conditions as it also was able to pick up the pocket at dry air at 300 where the

RH values near the tornadoes was hovering around 60% as seen in figure 56. However, there does not seem to be a gradient in RH near the vicinity of the outbreak region at all.

At 400hPa and 300 hPa the RH is between 60-70% while at 500 hPa and 700 hPa the RH is around 90%. The only RH gradient that can be seen at this time is at 300 hPa but it is located well south of the outbreak region and is a fairly weak gradient as well.

Overall none of the tornadoes associated with Tropical Storm Fay fell under any gradient in RH. There were occasions where very strong RH gradients were located yet they were too far removed from the outbreak region to accurately pinpoint the location of the tornadoes. The outbreaks proved difficult to analyze due to many of the same issues seen in the previous storms. The small number of tornadoes coupled with the distance in between them makes it difficult to say with confidence that the RH gradient can be used to pinpoint tornado outbreak regions.

Figure 52. Relative humidity for 300, 400, 500, and 700 hPa for 1800 UTC on 18 Aug. Images created using the European Centre for Medium-Range Weather Forecasts ERA- Interim reanalysis data within Matlab. Warmer colors indicate dry air while cooler colors indicate moist air. Black star indicates the location of the tropical cyclone at the current time. Dots represent the location of the various tornadoes that spawned at that time.

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Figure 53. Atmospheric profile sounding for Miami, Florida taken at 1200 UTC on Aug 19. Image was taken from the University of Wyoming Department of Atmospheric Science sounding page.

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Figure 54. Relative humidity for 300, 400, 500, and 700 hPa for 1200 UTC on 19 Aug. Images created using the European Centre for Medium-Range Weather Forecasts ERA- Interim reanalysis data within Matlab. Warmer colors indicate dry air while cooler colors indicate moist air. Black star indicates the location of the tropical cyclone at the current time. Dots represent the location of the various tornadoes that spawned at that time.

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Figure 55. Atmospheric profile sounding for Jacksonville, Florida taken at 1200 UTC on Aug 22. Image was taken from the University of Wyoming Department of Atmospheric Science sounding page.

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Figure 56. Relative humidity for 300, 400, 500, and 700 hPa for 1800 UTC on 22 Aug. Images created using the European Centre for Medium-Range Weather Forecasts ERA- Interim reanalysis data within Matlab. Warmer colors indicate dry air while cooler colors indicate moist air. Black star indicates the location of the tropical cyclone at the current time. Dots represent the location of the various tornadoes that spawned at that time.

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3.11 Frances (2004)

Hurricane Frances was a long lived powerful hurricane that originated from an active tropical wave off the coast of Africa. The system quickly became organized and reached tropical depression status on August 25th. The cyclone continued to intensify and was upgraded to tropical storm shortly after. Frances continued to deepen until it reached hurricane status and reached its first peak intensity with winds estimated at 115 kts on

August 28th. Frances began to weaken as a result of an eye wall replacement cycle however, quickly intensified until a second peak intensity was reached with winds at 125 kts making Frances a Category 4 storm by August 31st. Hurricane Frances was unable to maintain this strength for very long as increased wind shear and two more eye wall replacement cycles reduced winds to 85-90 kts. As a result Frances was downgraded to a

Category 2 storm by the time it reached the Bahamas. Frances eventually made landfall near Hutchinson Island, Florida around 0430 UTC on September 5th as a Category 2 storm. Frances weakened as it crossed Florida and did not reintensify when it reemerged over the Gulf before making a final landfall over the Florida panhandle on September 6th.

Frances track and intensity can be seen in figure 57.

Hurricane force winds impacted much of Florida which produced wide spread property damage as well as knocking down trees and power lines. Notable storm surge was recorded with the highest measurement recorded at just under six feet along the east coast of Florida. There were estimates that had storm surge as high as eight feet.

Flooding was another major concern with Hurricane Frances as heavy rain produced widespread fresh water flooding over the eastern United States. A maximum of 18 inches

105 was reported in North Carolina while much of Florida also reported rainfall in excess of

10 inches. Hurricane Frances produced a total of 101 tornadoes across five states. The majority occurred over North/South Carolina after the second landfall. A total of 67 tornadoes spawned with in the 24 hours before or after landfall and thus were included into this analysis. Overall, Hurricane Frances was the eight costliest hurricane according to NHC with a total estimate of 9.5 billion dollars in damages.

The first seven tornadoes occurred after 0000 UTC on September 5th across north east Florida (figure 58). Looking at the RH values based off the reanalysis data there is a strong gradient in RH stretching from northeast to southwest Florida at this time. At 300 and 400 hPa the RH gradient over the outbreak region dips from about 60% all the way to

20% incorporating all seven tornadoes. Dew point depression values based off the 0000

UTC sounding were above 10°C at these two levels. By 500 hPa the gradient weakens substantially with RH values over the outbreak region between 50-80%. However, the strongest portion of the gradient remains over the outbreak region. At 700 hPa the gradient continues to weaken with the strongest portion no longer located over the outbreak region but instead is located out to sea. There still is a weak gradient in place as all the tornadoes are under a region where the RH is 65%+. While the reanalysis data at the time seems to indicate that the RH gradient did an excellent job of pinpointing the outbreak location the observed data seems to contradict these findings. Figure 59 and 60 are the 0000 UTC soundings for Jacksonville and Miami Florida respectively. Based on the reanalysis data we should see multiple dry air intrusions over Jacksonville quickly becoming more saturated towards Miami. By looking at the soundings we can confirm

106 that the RH gradient seen in the reanalysis data was observed allowing for a more confident conclusion that the RH gradient accurately predicted the location of the outbreak region associated with the first seven tornadoes.

The next seven tornadoes occurred around 1800 UTC across northern Florida and southern Georgia. Unlike the initial seven tornadoes mentioned above this outbreak occurred under a much more saturated environment as seen in figure 61. At 300 hPa there is an extremely strong gradient to the north of the outbreak region. However, all seven tornadoes occur south of the gradient where the RH is well above 85%. Lower at 400 hPa the gradient weakens and shifts slightly to the south incorporating three tornadoes. At 500 hPa the gradient continues to weaken with most of the dry air retreating north. At this level only one of the tornadoes is located under the strongest portion of the RH gradient.

At 700 hPa the dry air pushes south again with the strongest portion of the RH gradient located across the Florida/Georgia border. As a result three tornadoes occur north of the gradient where the RH is less than 60%. The remaining four occur on the southern edge of the gradient where the RH is 80%. The observed soundings for Charleston, South

Carolina and Jacksonville, Florida (not shown) confirm that the RH was indeed in place at the time similar to what we saw above. As a result the RH gradient while not as accurate as the earlier outbreak was able to pinpoint the location of half the tornadoes at

400 and 500 hPa.

The next outbreak occurred just after 1200 UTC on September 6th where seven more tornadoes spawned across northern Florida and along the extreme southeast

Georgia/South Carolina border. Figure 62 depicts RH values at that time as well as the

107 location of the seven tornadoes. At all four levels on can see a large dry air intrusion being wrapped around towards the south of the tropical cyclone between Tampa and

Miami, Florida. At 300hPa all the tornadoes with the exception of one occur well north of the RH gradient present where the RH is 90%+. Lower at 400 hPa the RH gradient strengthens however, just like at 300 hPa only one tornado is near the gradient the rest occur under very saturated conditions at 400 hPa. At 500 hPa the dry air is able to push a bit further north but the overall strength of the gradient weakens once again. As a result of this northern push all the tornadoes are located on the northern fringe of the gradient yet the strongest portion is located much further south away from the tornadoes. By 700 hPa the dry air to the south retreats quite a bit and we are left with a scenario very similar to what was seen at 300/400 hPa. Overall this outbreak occurred under very saturated conditions confirmed by the observed 1200 UTC sounding for Jacksonville, Florida (not shown). As a result the RH gradient failed to pinpoint the location of the third tornado outbreak associated with Hurricane Frances.

The next outbreak occurred shortly after 1800 UTC on September 6th. This outbreak of tornadoes was located along southern South Carolina and northern Florida with an outlier located near Miami as seen in figure 63. Once again we see a dry air intrusion towards the south similar to what was seen during the 1200 UTC outbreak a few hours earlier. At 300 hPa the RH gradient is located to far south with all but one tornado being located under a region with 90%+ RH. At 400 hPa the dry air intrusion deepens and moves farther north incorporating the South Carolina tornadoes. However, the three

South Carolina tornadoes are located on the northern edge of the RH gradient with the

108 strongest portion located just off shore. The Florida tornadoes are also too far removed from the strongest portion of the gradient except for the one outlier near Miami which spawned under a region where the RH is about 40-50%. Lower at 500 hPa the dry slot moves further inland over southern South Carolina but the strength of the dry air intrusion weaken substantially. The low RH values between 40-50% seen just of the coast at 400hPa have retreated all the way down to southern Florida by 500 hPa. As a result the three tornadoes in southern South Carolina spawned in a region although slightly less saturated compared to its surroundings still occurred away from any major gradient in

RH. Three of the four Florida tornadoes occurred where the RH was 90% while the outlier tornado near Miami was located where RH values were around 60% but with no strong gradient nearby. At 700 while there is a RH gradient present it is fairly week leaving the majority of the tornadoes in a saturated environment where the RH is 80%+.

This was another example of the RH gradients failing to pick up on the location of the tornado outbreak.

Now up until this point the majority of the tornadoes were scattered across a large area and were small in size with none of the outbreaks producing more than seven tornadoes at a time. By 0600 UTC on September 7th the tornado outbreaks began to become large in size as the system began to interact with other mid latitude systems yet still maintain its weakened tropical status. Shortly after 0600 UTC Hurricane Frances spawned 13 tornadoes across South Carolina as seen in figure 64. Based on the four panel image of RH the majority of South Carolina is completely saturated throughout the entire column. This is confirmed by the observed sounding for 0000 UTC and 1200 UTC for

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Charleston, South Carolina (figure 65 and 66). The 0000 UTC sounding shows only 2-3 small pockets of dry air at the lower levels while remaining saturated aloft. By 1200

UTC the lower levels become more saturated while the upper levels begin to hint at drier air moving in. The 1200 UTC sounding could have been sampling the large RH gradient just north of the outbreak region seen at 300 hPa. Based off the reanalysis data the outbreak region occurred where the RH remained above 80% through all four levels. At

300hPa there is a very sharp gradient in RH to the north but doesn’t incorporate any of the tornadoes. By 400 hPa the RH gradient retreats north and at 500/700 hPa there is no strong gradient in RH anywhere near the outbreak region. There is a small dry air intrusion at 500 hPa with RH values below 70% attempting to move into the southern portion of the outbreak region but, it is too weak and removed to incorporate any of the tornadoes. This was the first major outbreak associated with Hurricane Frances which also made analysis easier as all the tornadoes were lumped together over a small region.

Unfortunately, the RH gradient once again failed to pinpoint the outbreak region. It is possible that the northern RH gradient seen at 300 and 400 hPa was able to slide far enough south between 0600-1200 UTC to incorporate the tornadoes on the northern fringe of the outbreak region.

The final outbreak that occurred within the first 24 hour after landfall was after

1200 UTC on September 7th where 26 tornadoes fell across Florida, South Carolina, and

North Carolina. Figure 67 shows the tornado locations along with the RH values form the reanalysis data. As one can see there are two distinct outbreak locations with plenty of dry air in the vicinity especially at the upper levels. At 300hPa the Carolina tornadoes are

110 sandwiched in between one sharp gradient to the north and a weaker more relaxed gradient to the south. However, the tornadoes did not spawn underneath these gradients unlike the findings by Curtis but instead spawned where the RH was consistently 90%.

The Florida tornadoes can be seen to have fallen in much drier conditions however the

RH gradient is not well defined in the area. The RH gradient associated with these tornadoes ranged from 40-60% which is not the sharp gradient in RH that match the findings by Curtis. At 400 hPa the strong sharp RH gradient to the north remains in placed verified by the Charleston, South Carolina and Newport, North Carolina soundings (not shown). Unfortunately the northern RH gradient still remains located too far off to the north to incorporate the Carolina outbreak. It’s possible that the gradient was able to slide south after 1200 UTC to incorporate some of the tornadoes on the northern edge of the outbreak region. The Florida tornadoes on the other hand are located under a weaker RH gradient that ranges from 40% on the southern edge to 70% to the north. For the first time since the initial outbreak mentioned at the start does the RH gradient line up with the outbreak region. This can also be seen at 500 hPa unlike the

Carolina tornadoes which have no RH gradient in the vicinity. By 700 hPa the gradient

RH values for both the Florida and Carolina outbreaks are high with no strong gradient located nearby.

Overall Hurricane Frances produced substantially more tornadoes compared to the previously discussed storms. Out of the six total outbreaks only two of them had RH gradients over the outbreak region. The other four outbreaks occurred under saturated conditions throughout the entire column. There were a few occasions where there was a

111 strong RH gradient present in the vicinity but was too far removed from the outbreak region. Further analysis would be needed to determine whether or not those strong RH gradient were able to move into the region during the six hours in between model runs.

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Figure 57. Best track positions for Hurricane Frances, 25 August – 8 September 2004.

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Figure 58. Relative humidity for 300, 400, 500, and 700 hPa for 0000 UTC on 5 September. Images created using the European Centre for Medium-Range Weather Forecasts ERA-Interim reanalysis data within Matlab. Warmer colors indicate dry air while cooler colors indicate moist air. Black star indicates the location of the tropical cyclone at the current time. Dots represent the location of the various tornadoes that spawned at that time.

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Figure 59. Atmospheric profile sounding for Jacksonville, Florida taken at 0000 UTC on September 05. Image was taken from the University of Wyoming Department of Atmospheric Science sounding page.

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Figure 60. Atmospheric profile sounding for Miami, Florida taken at 0000 UTC on September 5. Image was taken from the University of Wyoming Department of Atmospheric Science sounding page.

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Figure 61. Relative humidity for 300, 400, 500, and 700 hPa for 1800 UTC on 5 September. Images created using the European Centre for Medium-Range Weather Forecasts ERA-Interim reanalysis data within Matlab. Warmer colors indicate dry air while cooler colors indicate moist air. Black star indicates the location of the tropical cyclone at the current time. Dots represent the location of the various tornadoes that spawned at that time.

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Figure 62. Relative humidity for 300, 400, 500, and 700 hPa for 1200 UTC on 6 September. Images created using the European Centre for Medium-Range Weather Forecasts ERA-Interim reanalysis data within Matlab. Warmer colors indicate dry air while cooler colors indicate moist air. Black star indicates the location of the tropical cyclone at the current time. Dots represent the location of the various tornadoes that spawned at that time.

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Figure 63. Relative humidity for 300, 400, 500, and 700 hPa for 1800 UTC on 6 September. Images created using the European Centre for Medium-Range Weather Forecasts ERA-Interim reanalysis data within Matlab. Warmer colors indicate dry air while cooler colors indicate moist air. Black star indicates the location of the tropical cyclone at the current time. Dots represent the location of the various tornadoes that spawned at that time.

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Figure 64. Relative humidity for 300, 400, 500, and 700 hPa for 0600 UTC on 7 September. Images created using the European Centre for Medium-Range Weather Forecasts ERA-Interim reanalysis data within Matlab. Warmer colors indicate dry air while cooler colors indicate moist air. Black star indicates the location of the tropical cyclone at the current time. Dots represent the location of the various tornadoes that spawned at that time.

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Figure 65. Atmospheric profile sounding for Charleston, South Carolina taken at 0000 UTC on September 7. Image was taken from the University of Wyoming Department of Atmospheric Science sounding page.

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Figure 66. Atmospheric profile sounding for Charleston, South Carolina taken at 1200 UTC on September 7. Image was taken from the University of Wyoming Department of Atmospheric Science sounding page.

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Figure 67. Relative humidity for 300, 400, 500, and 700 hPa for 1200 UTC on 7 September. Images created using the European Centre for Medium-Range Weather Forecasts ERA-Interim reanalysis data within Matlab. Warmer colors indicate dry air while cooler colors indicate moist air. Black star indicates the location of the tropical cyclone at the current time. Dots represent the location of the various tornadoes that spawned at that time.

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3.11 Gabrielle (2001)

Gabrielle originated from a cut off low that was stationary over the southeastern United States. Eventually a surface low formed and convection began to develop and organize. The lack of any large scale synoptic features allowed the system to remain over the warm waters of the Gulf of Mexico where it was able to gradually strengthen until it was upgraded to tropical storm status on September 13th. At this time

Tropical Storm Gabrielle was located about 175 n mi southwest of Venice, Florida. A mid-level trough began to steer the cyclone to the northeast until landfall was made near

Venice, Florida at 1200 UTC on September 14th. Tropical Storm Gabrielle’s track and position can be seen in figure 68.

Rainfall totals from the storm were near 4-7 inches however many places including Volusia and Lake Counties recorded over 12 inches of rain. As a result many rivers and streams across Florida reached or surpassed flood stage. A total of 14 tornadoes were reported as a result of the tropical storm. One group of tornadoes touched down south of Tampa while another group touched down south of Jacksonville. A total estimate of 230 million dollars in damages was caused as a result of Tropical Storm

Gabrielle.

The first six tornadoes associated with Tropical Strom Gabrielle touched down shortly after 0600 UTC on September 14th across south central Florida as seen in figure

69. The tropical storm seems to be riding along the RH gradient to the west leaving much of Florida saturated with RH values above 90%. At 300 and 400 hPa there is a sharp gradient of to the west but it is far too removed to incorporate any of the tornadoes at

124 these levels. Lower at 500 hPa the gradient in RH weakens slightly yet remains in place leaving the RH values across Florida including the outbreak region to remain at 90%.

Finally at 700 hPa the RH gradient towards the west retreats while the gradient of to the east is able to advance towards the coast. This allowed some slightly drier are to push its way towards the outbreak region however, as seen in the previous levels the outbreak region occurred under a region where the RH remained around 90%. The 0600 observed sounding for Tampa, Florida matches the environment seen in the reanalysis data (figure

70) with a saturated environment through the column above Florida. This allowed for a confident conclusion that the RH gradient failed to locate the tornado outbreak region.

The final eight tornadoes occurred across northern Florida just after 1800 UTC on

September 14th after Tropical Storm Gabrielle moved onshore. The tornadoes all spawned relatively close to one another south of Jacksonville as seen in figure 71. The same image also indicates a dry air intrusion making its way across central Florida clearly visible at 300, 400 and 500hPa. However, this dry air intrusion is located to far south of the outbreak region seen in the 1800 UTC observed sounding (not shown) for Tampa,

Florida. Tropical Strom Gabrielle is located right along a moderately strong gradient in

RH however, all the tornadoes spawned further north where the environment was much more saturated with RH values around 90%. At 500 hPa the RH gradient advances north slightly but still remains too far south to incorporate the majority of the tornadoes. Finally at 700 hPa the gradient to the south is no longer present yet an RH gradient to the north can be seen advancing south. Once again a lack of an RH gradient at this level fails to recreate the findings found by Curtis. As seen in the first set of tornadoes the RH gradient

125 was present just not where the outbreak occurred allowing for a confident conclusion that the RH gradient for the second outbreak failed to pinpoint the outbreak region however, it was much closer compared to the initial outbreak at 0600 UTC.

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Figure 68. Best track positions for Hurricane Gabrielle, 11-19 September 2001. Track during the extratropical stage (after 19/0000 UTC) is based on analyses from the NOAA Marine Prediction Center. Inset is an enlargement of loop over southeastern Gulf of Mexico.

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Figure 69. Relative humidity for 300, 400, 500, and 700 hPa for 0600 UTC on 14 September. Images created using the European Centre for Medium-Range Weather Forecasts ERA-Interim reanalysis data within Matlab. Warmer colors indicate dry air while cooler colors indicate moist air. Black star indicates the location of the tropical cyclone at the current time. Dots represent the location of the various tornadoes that spawned at that time.

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Figure 70. Atmospheric profile sounding for Tampa, Florida taken at 0600 UTC on September 14. Image was taken from the University of Wyoming Department of Atmospheric Science sounding page.

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Figure 71. Relative humidity for 300, 400, 500, and 700 hPa for 1800 UTC on 14 September. Images created using the European Centre for Medium-Range Weather Forecasts ERA-Interim reanalysis data within Matlab. Warmer colors indicate dry air while cooler colors indicate moist air. Black star indicates the location of the tropical cyclone at the current time. Dots represent the location of the various tornadoes that spawned at that time.

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3.13 Gustav (2008)

Hurricane Gustav originally formed from a tropical wave off the coast of Africa with minor convective activity. Signs of organization did not show until August 18th however, heavy wind shear prevented any major intensification. Eventually wind shear decreased allowing for a more organization to occur until NHC upgraded the storm to a depression on August 25th. The cyclone then went under a period of rapid intensification as a small eye developed allowing the cyclone to be upgraded to hurricane status by 0000

UTC on August 26th. A large upper level ridge that built over the east coast of the United

States began to influence Gustav’s track turning the system westward by the 27th as it moved passed Hispaniola prompting the storm to weaken to 40 kts. The cyclone did not intensify again until it reached the warm waters in the northwest Caribbean Sea. Gustav rapidly intensified to a category 2 hurricane when it impacted the Cayman Islands and intensified into a category 4 hurricane when Gustav made landfall in Cuba around 1800

UTC on August 29th. Gustav reached its peak intensity around this time with wind speeds reaching 135 kt. The mountainous terrain over Cuba as well as strong vertical wind shear and dry air intrusion weaken Gustav until it made landfall as a Category 2 hurricane 1t 1500 UTC on September 1st near Cocodrie, Louisiana with maximum sustained winds near 90 kt. Hurricane Gustav’s track and intensity can be seen in figure

72.

Gustav caused widespread storm surge all along the Gulf Coast. While the Florida

Panhandle and Texas experienced above normal tides, surges of 12-13 feet occurred along the Louisiana coast. As a result the storm surge overtopped levees and floodwalls

131 in New Orleans. Fortunately, the flooding was not widespread. Heavy rainfall was another major hazard that accompanied Gustav which resulted in widespread freshwater flooding of many rivers in Louisiana and Arkansas. Larto Lake in Louisiana reported a storm total of 21 inches. A total of 41 tornadoes were produced with the majority of those occurring in Mississippi and Louisiana including an EF 2. For the purpose of this analysis only 21 of the 41 tornadoes spawned during the 24 hrs before or after landfall. Hurricane

Gustav caused a considerable amount of casualties and property damage along its path.

According to NHC a total of 112 deaths were directly linked to Gustav. In the United

States a total estimate of 4.6 billion dollars.

The first four tornadoes spawned shortly after 1200 UTC on September 1st. All the tornadoes were EF 0 located along the coast of the Florida panhandle as seen in figure

73. The 1200 UTC observed sounding for Tallahassee, Florida (figure 74) show multiple dry air intrusions throughout the entire column the largest being between 500 and

300hPa. The reanalysis data in figure 73 does an excellent job of picking up the dry air present around the outbreak region. At 300 hPa there is a large RH gradient to the south however, the outbreak region is located on the northern edge where RH values are around

90%. At 400 hPa the tornadoes are located right under an RH gradient. Even though it is not the strongest portion of the RH gradient the RH values over the tornadoes increase rapidly from 40% to just under 70%. At 500 hPa the RH gradient advances slightly and the gradient tightens. This was the best level to demonstrate the tornadoes spawning under a tight RH gradient similar to the finding by Curtis for this initial outbreak. The tornadoes at 500 hPa again spawn where the RH increases from 40% to 70% but at a

132 faster rate. Finally at 700 hPa any RH gradient has retreated away from the outbreak region leaving the tornadoes in a saturated environment with RH values above 80%.

Overall the RH gradient was able to accurately predict the location of the outbreak using the sharp gradient in RH.

The bulk of the tornadoes occurred after 1800 UTC on September 1st when 12 tornadoes spawned the majority of them occurring in Mississippi. Figure 75 shows the location of all 12 tornadoes as well as the RH values using the reanalysis data. At 300 hPa there is an extremely strong gradient pushing north through Mississippi which incorporates six tornadoes under the strongest portion of the RH gradient and three more just on the northern fringe. The tornadoes spawn with RH values increasing rapidly ranging from 30% all the way to 70%. This is the only level where we see the RH gradient line up with the outbreak region. Lower at 400 hPa the strongest portion of the

RH gradient retreats far to the east over Florida while a weaker gradient can be seen pushing south from the north. At this time only 2-5 tornadoes are located under some sort of RH gradient however, only the two tornadoes that occur along the Alabama/Florida border fall under the tightest portion of the RH gradient. The scenario at 500 hPa mirrors what was seen at 400 hPa the only difference being that the RH gradient along the

Alabama/ Florida border weakens quite a bit leaving the tornadoes in a more saturated environment compared to 400 hPa. Finally at 700 hPa any RH gradient is far removed from the outbreak region leaving a saturated environment with RH values above 80%.

While 300 hPa did fairly decent job at pinpointing the tornado outbreak using the strong

RH gradient, the lack of a proper atmospheric sounding limits the ability to validate the

133 strength/location of the strong of said gradient seen at 300 hPa. As a result we are only left with moderate confidence that the results shown here match the findings by Curtis.

The final five tornadoes spawned around 1200 UTC on September 2 in

Mississippi. Figure 76 indicates the tornadoes were limited to central Mississippi. At 300 hPa the tornadoes are located under a moderate RH gradient ranging from 40-80% along the outbreak region. Similar to what was seen in the previous outbreak 300 hPa is the only level in which the outbreak region is aligned with an RH gradient. At 400 hPa the

RH gradient is completely removed leaving the outbreak region in an area where RH values are 90%. The same thing can be seen at 500 hPa with the exception of drier air being to push west as seen with the slight RH gradient seen along the

Mississippi/Alabama border. At 700 hPa this same gradient continues to push west yet never fully makes it to the outbreak region as RH values remain above 70%. Unlike the previous outbreak there is a much higher confidence that the RH gradient pinpointed the location of the tornado outbreak at 300 hPa based on the soundings available. Figure 77 and 78 show the observed atmospheric soundings at 1200 UTC for Jackson, Mississippi and Tallahassee, Florida respectively. The Jackson sounding which was situated on the northern edge of the RH gradient indicates a saturated environment throughout the entire column with drier air working its way in above 400 hPa similar to what was seen in figure 76. The Tallahassee sounding indicates large pockets of dry air at varies levels of the atmosphere especially at 300 hPa. This helps validate that the RH gradient shown in the reanalysis data was present at the time allowing for a more confident conclusion that the RH gradient was able to pinpoint the location of the tornado outbreak.

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Figure 72. Best track positions for Hurricane Gustav, 25 August – 4 September 2008. Track during the extratropical stage is based on analyses from the NOAA Hydrometeorological Prediction Center.

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Figure 73. Relative humidity for 300, 400, 500, and 700 hPa for 1200 UTC on 1 September. Images created using the European Centre for Medium-Range Weather Forecasts ERA-Interim reanalysis data within Matlab. Warmer colors indicate dry air while cooler colors indicate moist air. Black star indicates the location of the tropical cyclone at the current time. Dots represent the location of the various tornadoes that spawned at that time.

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Figure 74. Atmospheric profile sounding for Tallahassee, Florida taken at 1200 UTC on September 1. Image was taken from the University of Wyoming Department of Atmospheric Science sounding page.

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Figure 75. Relative humidity for 300, 400, 500, and 700 hPa for 1800 UTC on 1 September. Images created using the European Centre for Medium-Range Weather Forecasts ERA-Interim reanalysis data within Matlab. Warmer colors indicate dry air while cooler colors indicate moist air. Black star indicates the location of the tropical cyclone at the current time. Dots represent the location of the various tornadoes that spawned at that time.

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Figure 76. Relative humidity for 300, 400, 500, and 700 hPa for 1200 UTC on 2 September. Images created using the European Centre for Medium-Range Weather Forecasts ERA-Interim reanalysis data within Matlab. Warmer colors indicate dry air while cooler colors indicate moist air. Black star indicates the location of the tropical cyclone at the current time. Dots represent the location of the various tornadoes that spawned at that time.

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Figure 77. Atmospheric profile sounding for Jackson, Mississippi taken at 1200 UTC on September 2. Image was taken from the University of Wyoming Department of Atmospheric Science sounding page.

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Figure 78. Atmospheric profile sounding for Tallahassee, Florida taken at 1200 UTC on September 2. Image was taken from the University of Wyoming Department of Atmospheric Science sounding page.

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3.14 Ike (2008)

Ike originally developed from a well-organized tropical wave that moved off the coast of Africa on August 28th. The system moved went into the Atlantic producing on and off convection until it was upgraded to a tropical depression. A strong upper level ridged helped steer the system west where it quickly strengthen to a tropical storm by

1200 UTC on September 1st. At this point a significant layer of dry air surrounding the cyclone prevented any further intensification. As the atmosphere around the cyclone became more saturated, strong convection developed and an eye developed which combined with estimated wind speed reports prompted NHC to upgrade the tropical storm to a hurricane by 1200 UTC on September 3rd. As the ridge to the north weakened

Hurricane Ike track began to shift to the west-northwest where a peak intensity of 125 kt winds were recorded which was a 70 kt increase in 24hrs. Ike’s rapid intensification was short lived as another high pressure system over the western Atlantic produced enough wind shear where the storm became asymmetric. As a result, Ike’s sustained wind speed fell to 95 kts by 1200 UTC on September 6th. As the wind shear weakened Ike was quickly able to reorganize back into a category 4 Hurricane near the Turks and Caicos

Islands. Land interaction helped weaken Ike lightly as it passed just south of the Turk and

Caicos before making landfall in the Bahamas around 1300 UTC on September 7th. By

0000 UTC on September 8th Ike was once again a category 4 hurricane with sustained winds at 155 kts as it moved through Cuba. Much of the cyclones inner core was destroyed as the hurricane moved across Cuba which significantly impacted Ike’s strength once it reemerged into the southeastern Gulf of Mexico. Ike would have

142 difficulty re organizing as it moved towards the northwest eventually making landfall near Galveston Island, Texas at 0700 UTC on September 13th. The cyclone quickly became extratropical after landfall producing hurricane forced gust as far north as the

Ohio River Valley. Ike’s track and intensity can be seen in figure 79.

Due to the Hurricanes large size much of the Gulf Coast was impacted by storm surge. Florida experienced storm surge around 1-3 feet. Farther west along Alabama,

Mississippi, and eastern Louisiana experienced storm surge around 3-6 feet. Storm surge increased rapidly west of the Mississippi River delta. Central Louisiana saw storm surge between 5-10 feet while along the Louisiana/Texas boarder storm surged reached as high as 10-13 feet. Near Galveston storm surged reached 10-15 ft while the Southern Texas coast line recorded storm surges around 5 feet. The majority of the area west of the southern Texas/Louisiana border saw rainfall amounts from 7-15 inches. Around 28 tornadoes were reported as a result of Ikea across Louisiana, Texas, and Arkansas. None were reported to be higher than an EF 1. Unfortunately, Ike is responsible for 103 direct deaths along its path through the Caribbean and United States. Ike caused significant economic woes across the coast as oil rigs, refineries, and ports were forced to shut down in anticipation of Ike. An estimated 2.6 million people lost power as a result of the strong winds while the strong storm surged leveled homes along the coast. According to NHC,

Ike produced an estimated 29.52 billion dollars in damages making it the second costliest hurricane to affect the United States after Hurricane Katrina.

The first five tornadoes spawned across south western Louisiana after 1800 UTC

September 12th as seen in figure 80. Figure 80 also shows the RH values at 1800 using

143 the reanalysis data. One can see that there is a very large pocket of dry air over the outbreak region especially at 300 and 400 hPa. At 300 hPa the RH values increase rapidly from 20% over central Louisiana to 70% just off the coast. The majority of the tornadoes spawned where the RH value is 20% just north of where the strongest portion of the RH gradient was located. At 400 hPa the pocket of dry air deepens with RH values increasing rapidly once again from 10% over central Louisiana to 70% just off the coast. However, similar to what was seen at 300 hPa the tornadoes spawned where the RH values were around 10-20% which was located north of where the strongest portion of the RH gradient was located. Observed 1800 UTC sounding for Lake Charles, Louisiana (figure

81) confirms just how dry the air aloft. By 500 hPa the environment near the tornadoes quickly becomes saturated with RH values near 70% and far removed from any RH gradient which has retreated to the northwest. Lower at 700 hPa the only gradient in RH in the area is located well off the coast leaving much of the outbreak region under an area where the RH values range from 60-80%. While there was a strong gradient in RH located near the outbreak region at 300 and 400 hPa the strongest portion of the gradient however, did not occur over the same region the tornadoes occurred allowing the conclusion that the RH while very closed failed to pinpoint the exact location of the tornado outbreak.

The next nine tornadoes occurred after 1200 UTC on September 13th. Figure 82 shows that the majority of the tornadoes were concentrated over northern Louisiana east of Shreveport with one outlier in eastern Texas. At 300 hPa there is a very strong RH gradient located in between the tornado in Texas and the tornadoes in Louisiana.

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Unfortunately, the strongest portion of the RH gradient is located away from where the tornadoes occurred. The Louisiana tornadoes are located where the RH is 10% while the

Texas tornado is located where the RH is 70%. Similar results are seen at 400 hPa where the RH gradient remains in place and pushes southwest where it incorporates the Texas tornado. This gradient is confirmed to be present based on the 1200 UTC soundings for

Shreveport and Lake Charles, Louisiana. Figure 83 shows an extremely saturated environment near the surface fairly saturated column above Lake Charles before beginning to dry out above 400 hPa. Figure 84 shows a very strong pocket of dry air that moves through between 500 hPa and 250 hPa. While it’s confirmed that the RH gradient was present at the time the RH gradient only incorporates one tornado. Confidence is extremely low on whether the gradient did indeed pinpoint the outbreak location due to the small sample size. The gradient at 500 hPa retreats northeast causing the Louisiana tornadoes to finally be incorporate in a mild gradient in RH were the RH values increase from 60-80% over the outbreak region. The strongest portion of the RH gradient is still located towards the south east away from the outbreak region. Finally at 700 hPa the Rh gradient continues to retreat east leaving much of the outbreak area under saturated conditions where the RH values are about 80%. Overall while the RH gradient was the strongest at 300 and 400 hPa the much weaker gradient at 500 hPa was the only gradient to incorporate the majority of the tornadoes. However, the strongest portion of the RH gradient failed to pinpoint the tornado outbreak region at any of the four levels contradicting the findings by Curtis.

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The largest outbreak associated with Hurricane Ike occurred after 1800 UTC on

September 13th where 14 tornadoes spawned across Louisiana, Arkansas, and

Mississippi. At 300 hPa a strong RH gradient can be seen east of the location of the hurricane incorporating three of the Louisiana tornadoes within the strongest portion of the gradient (figure 85). The majority of the tornadoes occurred where the RH was about

10%. At 400 hPa the RH retreats east however, now eight of the tornadoes are located under the strongest portion of the RH gradient. This is the best example during Hurricane

Ike that had results that agreed with the findings by Curtis. The RH gradient over those eight tornadoes increases rapidly from 10-60%. At 500 hPa the RH gradient weakens substantially only incorporation two tornadoes while at 700 hPa the RH over the entire outbreak region is between 70-80%. Soundings for Little Rock, Arkansas and Shreveport,

Louisiana (not shown) confirm the location of the outbreak. As a result the RH gradient did an excellent job of pinpointing the tornado outbreak region at 400 hPa. The RH gradient at 300 hPa did a moderate job of pinpointing the tornado outbreak region as the

RH gradient was able to incorporate a few of the tornadoes however, the bulk of the tornadoes were located just east of said gradient.

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Figure 79. Best track positions for Hurricane Ike, 1 – 14 September 2008. Track during the extratropical stage is based on analyses from the NOAA Hydrometeorological Prediction Center and Environment Canada.

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Figure 80. Relative humidity for 300, 400, 500, and 700 hPa for 1800 UTC on 12 September. Images created using the European Centre for Medium-Range Weather Forecasts ERA-Interim reanalysis data within Matlab. Warmer colors indicate dry air while cooler colors indicate moist air. Black star indicates the location of the tropical cyclone at the current time. Dots represent the location of the various tornadoes that spawned at that time.

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Figure 81. Atmospheric profile sounding for Lake Charles, Louisiana taken at 1800 UTC on September 12. Image was taken from the University of Wyoming Department of Atmospheric Science sounding page.

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Figure 82. Relative humidity for 300, 400, 500, and 700 hPa for 1200 UTC on 13 September. Images created using the European Centre for Medium-Range Weather Forecasts ERA-Interim reanalysis data within Matlab. Warmer colors indicate dry air while cooler colors indicate moist air. Black star indicates the location of the tropical cyclone at the current time. Dots represent the location of the various tornadoes that spawned at that time.

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Figure 83. Atmospheric profile sounding for Lake Charles, Louisiana taken at 1200 UTC on September 13. Image was taken from the University of Wyoming Department of Atmospheric Science sounding page.

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Figure 84. Atmospheric profile sounding for Shreveport, Louisiana taken at 1200 UTC on September 13. Image was taken from the University of Wyoming Department of Atmospheric Science sounding page.

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Figure 85. Relative humidity for 300, 400, 500, and 700 hPa for 1800 UTC on 13 September. Images created using the European Centre for Medium-Range Weather Forecasts ERA-Interim reanalysis data within Matlab. Warmer colors indicate dry air while cooler colors indicate moist air. Black star indicates the location of the tropical cyclone at the current time. Dots represent the location of the various tornadoes that spawned at that time.

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3.15 Irene (2011)

Irene originated from a very active tropical wave that moved off the coast of

Africa around August 15th. The system went through varies cycles of growth and decay as it moved across the Atlantic. The cyclone was able to maintain a mid-level circulation and the system was classified as a tropical storm around 0000 UTC on August 21st.

Tropical Storm Irene continued to grow and organize as it moved through the northeast

Caribbean Sea. The cyclone was upgraded to a hurricane as it moved passed Puerto Rico around 0600 UTC on August 22nd. Even though Hurricane Irene was moving through a favorable environment for intensification, land interaction with both Puerto Rico and

Hispaniola delayed any further intensification. Irene then reached peak intensity as a category 3 Hurricane on August 24th after passing through Hispaniola with winds speeds reaching 105 kts. The cyclone began to weaken as it moved to the northwest until landfall was made near Cape Lookout, North Carolina around 1200 UTC on August 27th as a category 1 hurricane. A second landfall was made near Atlantic City, New Jersey with 60 kt winds being reported no August 28th. Luckily the strongest winds were located well off shore as the center of rotation moved over New York City. Irene continued to move north until it was absorbed by a frontal system. Irene’s track and intensity can be seen in figure 86.

As a result of Irene’s large size much of the east coast received rainfall anywhere between 5-10 inches. A maximum of 15.74 inches was reported in Bayboro, North

Carolina. Storm surge also impacted much of the east coast with reports of storm surge of

4-6 feet along the New Jersey coastline northward and reports of 8-11 ft father south

154 along North Carolina. A total of 9 tornadoes were spawned across including two EF 1 tornadoes in North Carolina and two EF 0 tornadoes in New York. The strong winds, storm surge, and torrential rain that impacted much of the east coast especially New

England with serious flash floods that destroyed homes, roads, business and railroad tracks resulted in an estimated 15.8 billion dollars I damages as a result of Irene.

The first three tornadoes occurred along the North Carolina coastline after 0000

UTC on August 26th. Based on the reanalysis data used to create the RH image seen in figure 87 there is a large dry air intrusion over the outbreak region in three of the four levels analyzed. This dry air intrusion contradicts what was observed on the 0000 UTC sounding for Newport, North Carolina. The sounding seen on figure 88 shows a very large dry air intrusion around 700 but remains fairly saturated as one moves up the atmosphere. At 300 hPa there is a strong RH gradient located just south of the outbreak region. The tornadoes however, spawned where the RH was constant around 30%. Lower at 400 hPa the RH gradient remains in place and strengthens slightly. The strongest portion of the RH gradient once again remains too far south to incorporate the three tornadoes. At 500 hPa the RH gradient continues to sit off the North Carolina coast away from where the tornadoes occurred. The tornadoes spawned where the RH remain constant around 20%. Finally at 700 hPa the environment becomes more saturated and the RH gradient off the coast is nonexistent. Overall while there was a strong RH gradient near the vicinity of the outbreak region in three of the four levels, the gradient did fail to pinpoint the location of the tornadoes. The lack of agreement between observed data and

155 the reanalysis data also make it difficult to say with confidence if the strong RH gradient was there at the time.

The next three tornadoes occurred after 1200 UTC on August 27th when two tornadoes spawned in Virginia and one in Delaware. At 300 hPa (figure 89) the environment near the tornadoes is completely saturated where RH values are between 90-

100%. Lower at 400 a strong RH gradient can be seen to the northwest however, the strongest portion of the RH gradient is far removed from the tornadoes to incorporate any. The same thing is seen at 500 hPa. While the gradient does indeed push further south the strongest portion of the RH gradient is located over northern Virginia/Delaware. The tornadoes continued to be located where the RH is 80% or higher. Finally at 700 hPa there is no trace of any RH gradient in the vicinity of the outbreak region. RH values along the coast of the Mid-Atlantic States were 80% or higher. Once again the reanalysis data seems to contradict what was observed based on the soundings taken at the time.

Figure 90 is the 1200 UTC sounding for Wallops Island, Virginia. Based on the reanalysis data the sounding should be saturated up through the entire column. However, the sounding shows multiple pockets of dry air especially at the lower levels all the way up to 500 hPa before it becomes more saturated. The reanalysis data shows no indication of dry air in the lower levels especially at 700 hPa. While the RH gradient again failed to pinpoint the location of the tornadoes confidence in the statement is extremely low due to contradicting data between observed and the reanalysis.

The final three tornadoes spawned around 0600 UTC on August 28th in New York and New Jersey. Looking at the RH reanalysis data in figure 91 one can see that the

156 environment is extremely saturated at all the levels analyzed. At 300 hPa there is an RH gradient located well off the coast leaving the outbreak region with RH values between

80-90%. At 400 hPa the RH gradient mentioned above is no longer visible leaving the outbreak region with RH values ranging from 70-80%. The same thing can be seen at 500 and 700 hPa where the environment near the tornadoes is completely saturated with RH values between 70-80% and no RH gradient in sight. However, once again we see a conflict between the observed and the reanalysis data. Observed soundings for 0000 UTC and 1200 UTC from Upton, New York (not shown) indicates dry air below 400 hPa during both the 0000 and 1200 UTC balloon launch that is not being picked up by the reanalysis data. The soundings seems to indicate that there may indeed have been a gradient in RH present near the outbreak region but lack of agreeing data make the confidence for such a statement low. Overall, the reanalysis data had trouble matching the observed data for all three of the days that spawned tornadoes which is something that was not seen with the previous storms. This allows me to believe the issue is only limited to these few days rather than the reanalysis data as a whole.

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Figure 86. Best track positions for Hurricane Irene, 21 -28 August 2011. Track during the extratropical stage is based on analyses from the NOAA Hydrometeorological Prediction Center

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Figure 87. Relative humidity for 300, 400, 500, and 700 hPa for 0000 UTC on August 26th. Images created using the European Centre for Medium-Range Weather Forecasts ERA-Interim reanalysis data within Matlab. Warmer colors indicate dry air while cooler colors indicate moist air. Black star indicates the location of the tropical cyclone at the current time. Dots represent the location of the various tornadoes that spawned at that time.

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Figure 88. Atmospheric profile sounding for Newport, North Carolina taken at 0000 UTC on August 26. Image was taken from the University of Wyoming Department of Atmospheric Science sounding page.

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Figure 89. Relative humidity for 300, 400, 500, and 700 hPa for 1200 UTC on August 27th. Images created using the European Centre for Medium-Range Weather Forecasts ERA-Interim reanalysis data within Matlab. Warmer colors indicate dry air while cooler colors indicate moist air. Black star indicates the location of the tropical cyclone at the current time. Dots represent the location of the various tornadoes that spawned at that time.

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Figure 90. Atmospheric profile sounding for Wallops Island, Virginia taken at 1200 UTC on August 27. Image was taken from the University of Wyoming Department of Atmospheric Science sounding page.

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Figure 91. Relative humidity for 300, 400, 500, and 700 hPa for 0600 UTC on August 28th. Images created using the European Centre for Medium-Range Weather Forecasts ERA-Interim reanalysis data within Matlab. Warmer colors indicate dry air while cooler colors indicate moist air. Black star indicates the location of the tropical cyclone at the current time. Dots represent the location of the various tornadoes that spawned at that time.

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3.16 Ivan (2004)

Hurricane Ivan was a long lived system which reached Category 5 strength three times as it moved across the Atlantic. Ivan originally developed from a tropical wave that moved west off the coast of Africa in August 31st. While the tropical waved looked impressive on paper satellite data indicated that convection was weak and unorganized.

Convection did begin to develop and deepen as the system moved into an area of weak shore allowing the system to intensify into a tropical depression by 1800 UTC in

September 2nd. 12 hours later the system was upgraded to Tropical Storm Ivan as development continued to increase. Ivan reached hurricane strength a few days later on

September 5th as the cyclone continued to move westward. It was at this point that

Hurricane Ivan went through a period of drastic rapid intensification that saw wind speeds increase more than 30 kt in a 24 hour period while the central pressure dropped almost 40hPa during that time. This allowed Ivan to reach its first peak intensity as 115 kt winds at 0000 UTC on September 6. This also made Ivan the southernmost storm on record while at a latitude of 9.7*N. However, shortly after this period of rapid intensification a layer of dry air was able to entrain itself around the storm causing a rapid drop in strength. Again Ivan was able to reorganize and strengthen into a Category 3 storm when it passed just south of Grenada. By 1800 UTC in September 8th Ivan reached its second peak intensity with 140 kt winds prompting NHC to upgrade Hurricane Ivan to a category 5 hurricane. An eyewall replacement cyclone helped weaken Hurricane Ivan to a category 4 system as it passed just south of Jamaica. However, warm waters and low shear allowed Ivan to reach Category 5 strength once again with a peak intensity of 145

164 kts by 1800 UTC on September 11th. A period of weakening was followed by another period of rapid growth allowing Hurricane Ivan to reach Category 5 strength for a third and final time when the cyclone was located just 80 n mi west of Grand Cayman Island.

Ivan maintained its Category 5 strength as it moved through the Yucatan Peninsula until it reemerged into the Gulf of Mexico where shear associated with an upper level trough began to weaken Hurricane Ivan. The vertical shear, cool waters, and dry air intrusion unfortunately was able to weaken the system fast enough allowing Hurricane Ivan to make landfall just west of Gulf Shores, Alabama by 0700 UTC on September 16th. At this point the system turned towards the northeast and quickly began to weaken eventually merging with a frontal system over the Delmarva Peninsula. However, even as the system weakened Ivan was an active rain and tornado producer. Ivan’s strength and intensity can be seen in figure 92.

Category 3 winds impacted the Gulf Coast causing wide spread property damage as well as disrupting power to as much as 1.8 million along the coast. The dangerous wind speeds also contributed to the damaging storm surge that was felt along the coast.

From the Florida panhandle all the way to Mobile Bay storm surged reached heights of

10-15ft which forced officials to close the interstate bridge system across Pensacola Bay,

Florida. The dangerous waves leveled thousands of homes as well as destroyed acres of woodlands and forests. Oil operations off shore were also severely interrupted as oil platforms and pipelines were damaged. Ivan caused an estimated 18.82 billion dollars in damages.

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Ivan was also produced a wide spread tornado outbreak with more than 100 tornadoes being reported. Eight states were affected by the outbreak that developed over a three day period. For the purpose of this paper a total of 58 tornadoes were analyzed.

Ivan created to swath of tornadoes following the diurnal cycle of the storm.

The first 21 tornadoes Spawned by Hurricane Ivan occurred after 1800 UTC on

September 15th. Figure 93 shows that the tornadoes were isolated to southern

Alabama/Georgia and the Florida Panhandle. At 300 hPa there is a gradient off to the northwest however, the strongest portion of the RH gradient is located in Mississippi.

The RH values over the region where the tornadoes occurred remain constant at around

90%. At 400 hPa the RH gradient pushes southeast and strengths. Once again the strongest portion of the RH gradient is located in southern Mississippi and extreme southeast Louisiana. As a result none of the tornadoes are located under the tight gradient but instead are located where the RH values remain constant at 90%. Lower at 500 hPa the strong RH gradient retreats west. This allows some drier air to begin to move over the outbreak region from the southeast however, much of the environment remains saturated as RH values only dip to 80%. Finally at 700 hPa the dry air continuous to work its way over the outbreak region lowering RH values to about 60%. There is also no strong gradient in RH present at this level. The observed sounding data matches what is shown in the reanalysis data. Figure 94 shows the 1800 UTC sounding for Slidell Muni,

Louisiana. At this time one can see a large dry air intrusion starting at 500 hPa continuing all the way up to 350 hPa. This dry air intrusion is located over the same region the reanalysis data has the strong RH gradient at 400 hPa. Farther west over Tallahassee the

166 environment is extremely saturated though out the entire column as seen in figure 95.

This confirms that the RH gradient was indeed in place at the time. This allows a more confident conclusion in the fact that the RH gradient while in the vicinity of the outbreak region failed to pinpoint the exact location of the tornado outbreak using the location of the strongest portion of the RH gradient.

The following seven tornadoes occurred after 0000 UTC on September 16th.

Figure 96 shows that all the tornadoes were located over Florida. At 300 hPa the whole state of Florida is completely saturated with RH values near 90% over where the seven tornadoes spawned. A similar situation is seen at 400 hPa where some drier air is seen moving in from the east however; there is no RH gradient in place over Florida where the

RH values remain constant ranging from 70-90%. Lower at 500 hPa much drier air begins to move into Florida from the southeast. As a result a strong RH gradient is located throughout central Florida. The strongest portion of the RH gradient is located just east of the tornadoes located near Tampa. The RH values over the Florida Panhandle tornadoes remain constant between 70-80%. Finally at 700 hPa the strong RH gradient seen at 500 hPa retreats back east allowing more saturated air to move back over the majority of Florida. At this time RH values over the outbreak region range from 70-80%.

Observed sounding data from Tallahassee (not shown) and Tampa (figure 97) confirm the conditions illustrated by the reanalysis data. The Tampa sounding clearly shows the gradient of dry air present especially at 500 hPa. As a result the RH gradient while not perfect was very close at locating the tornado outbreak. The RH gradient would have needed to be located slightly more towards the northwest to match the findings by Curtis.

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The third outbreak occurred after 0600 UTC on September 16th. Figure 98 shows that the majority of the tornadoes were located over southeastern Alabama with an additional two over Georgia and Florida. Figure 98 also shows the RH values over the southeast at 0600 UTC the same day. At 300 hPa the environment over all the tornadoes is completely saturated where RH values are between 90-100%. The only RH gradient is well off to the over Louisiana/Mississippi. At 400 hPa the gradient to the west remains in place but, another RH gradient can be seen incorporating the majority of the Florida peninsula. This RH gradient however, remains too far off to the southeast to incorporate any of the tornadoes. Only one tornado is located along the northern fringe of the RH gradient where the RH is between 50-60%. The rest of the tornadoes continue to be located under saturated conditions at 400 hPa where the RH is above 80%. Lower at 500 hPa a dry slot can be seen working its way through the Florida panhandle. This dry air intrusion incorporates a total of four tornadoes but only two are located near the strongest portion of the RH gradient where the RH is near 50%. The majority of the tornadoes once again remained away from any RH gradient. The 0000 UTC and 1200 UTC soundings for Tallahassee, Florida confirm the presence of the dry air intrusion to the east. At 0000

UTC (figure 99) the environment over Tallahassee remains saturated throughout the entire column. Fast-forward 12 hours to the 1200 UTC sounding (figure 100) and one can see multiple pockets of dry air over Tallahassee especially at 500 hPa. This indicates that the dry air seen in the reanalysis data was able to continue to push west somewhere between 0600 and 1200 UTC. One can now state with confidence that the RH gradient failed to pinpoint the location of the outbreak region at 500 hPa. Finally at 700 hPa much

168 of the southeast becomes saturated again. At this level only one tornado forms where the

RH values are below 70% near a very weak RH gradient over central Georgia.

The final 22 tornadoes included in this study occurred after 1800 UTC on

September 16th. Figure 101 illustrates that the tornadoes were located along the

Georgia/South Carolina border. At 300 hPa the environment over the outbreak region is very saturated with RH values above 90% for all of Georgia and South Carolina. The only RH gradient at this level is off to the south west along the southern

Mississippi/Alabama border. At 400 hPa the RH gradient to the southwest remains in place however, dry air is beginning to wrap in towards the outbreak region from the south east. Even with the dry air progressing north the outbreak region remains saturated. Only two tornadoes form where the RH is less than 80%. The large majority of the tornadoes continue to be located where the RH is above 90%. Lower at 500 hPa more dry air continuous to push north however, the gradient remains weak. None of the tornadoes are incorporated within the strongest portion of the RH gradient. Two tornadoes form where the RH is 70% while the rest form where the RH is 80% or higher. Finally at 700 hPa much drier air is finally able to enter the outbreak region. The strongest portion of the RH gradient which has RH values quickly increasing from 50-80% is located right over the bulk of the tornadoes that formed along the Georgia/South Carolina Border. Only three to five tornadoes or located away from the gradient. Soundings from Peach Tree City,

Georgia and Charleston, South Carolina (not shown) help verify that the dry air intrusion seen in the reanalysis data matches what was observed. As a result one can say with confidence that the strongest portion of the RH gradient at 700 hPa was able to accurately

169 predict the location of the tornado outbreak that occurred after 1800 UTC on September

16th. Out of the four separate outbreaks analyzed during Hurricane Ivan only one level during one outbreak was able to get results matching the findings by Curtis.

170

Figure 92. Best track positions for Hurricane Ivan, 2-24 September 2004

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Figure 93. Relative humidity for 300, 400, 500, and 700 hPa for 1800 UTC on September 15th. Images created using the European Centre for Medium-Range Weather Forecasts ERA-Interim reanalysis data within Matlab. Warmer colors indicate dry air while cooler colors indicate moist air. Black star indicates the location of the tropical cyclone at the current time. Dots represent the location of the various tornadoes that spawned at that time.

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Figure 94. Atmospheric profile sounding for Slidell Muni, Louisiana taken at 1800 UTC on September 15. Image was taken from the University of Wyoming Department of Atmospheric Science sounding page.

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Figure 95. Atmospheric profile sounding for Tallahassee, Florida taken at 1800 UTC on September 15. Image was taken from the University of Wyoming Department of Atmospheric Science sounding page.

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Figure 96. Relative humidity for 300, 400, 500, and 700 hPa for 0000 UTC on September 16th. Images created using the European Centre for Medium-Range Weather Forecasts ERA-Interim reanalysis data within Matlab. Warmer colors indicate dry air while cooler colors indicate moist air. Black star indicates the location of the tropical cyclone at the current time. Dots represent the location of the various tornadoes that spawned at that time.

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Figure 97. Atmospheric profile sounding for Tampa, Florida taken at 0000 UTC on September 16. Image was taken from the University of Wyoming Department of Atmospheric Science sounding page.

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Figure 98. Relative humidity for 300, 400, 500, and 700 hPa for 0600 UTC on September 16th. Images created using the European Centre for Medium-Range Weather Forecasts ERA-Interim reanalysis data within Matlab. Warmer colors indicate dry air while cooler colors indicate moist air. Black star indicates the location of the tropical cyclone at the current time. Dots represent the location of the various tornadoes that spawned at that time.

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Figure 99. Atmospheric profile sounding for Tallahassee, Florida taken at 0000 UTC on September 16. Image was taken from the University of Wyoming Department of Atmospheric Science sounding page.

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Figure 100. Atmospheric profile sounding for Tallahassee, Florida taken at 1200 UTC on September 16. Image was taken from the University of Wyoming Department of Atmospheric Science sounding page.

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Figure 101. Relative humidity for 300, 400, 500, and 700 hPa for 1800 UTC on September 16th. Images created using the European Centre for Medium-Range Weather Forecasts ERA-Interim reanalysis data within Matlab. Warmer colors indicate dry air while cooler colors indicate moist air. Black star indicates the location of the tropical cyclone at the current time. Dots represent the location of the various tornadoes that spawned at that time.

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3.17 Jeanne (2004)

Jeanne originally formed as a tropical wave that moved off the coast of Africa on

September 7th. Convective activity was nonexistent as the system moved across the

Atlantic. Once the system approached the Leeward Islands enough organization was show to upgrade the system to a tropical depression. A large sub-tropical high helped steer the depression to the west and was upgraded once again on September 14th. Tropical storm Jeanne continued its extremely slow track across the Caribbean impacting the

Virgin Islands, Puerto Rico and the Dominican Republic whose terrain helped weaken

Jeanne back into a tropical depression. It wasn’t until September 23rd that Jeanne was able to reorganize into a hurricane. Jeanne meandered near the Bahamas for a few days until landfall was made along the east coast of Florida near Hutchinson Island at 0400

UTC on September 26th. Hurricane Jeanne quickly weakened into a tropical storm when it was located near Tampa producing heavy rain until the system was absorbed by a passing frontal system by 0000 UTC on September 29th. Hurricane Jeanne’s track and strength can be seen in figure 102.

Much of Florida received rainfall as high as 8 inches while reports of 11-13 inches were observed along the track of the eye wall. Rainfall reports of 4-7 inches were reported father north in portions of Georgia, Virginia, and the Carolinas. Minimal storm surge was reported along the Florida coast with reports around 4 ft. Overall, the storm surge caused minor disruptions along the coast. 10 tornadoes were reported throughout

Florida. Fortunately, the tornadoes rated EF0 caused were little damage. A total estimate of 7.66 billion dollars in damages was reported as a result of Hurricane Jeanne.

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The first three tornadoes occurred just after 0000 UTC on September 26th between

Jacksonville and Miami, Florida. Figure 103 shows the tornado locations as well as the

RH values using the European Centre for Medium-Range Weather Forecasts ERA-

Interim reanalysis data. At 300 hPa while the tropical cyclone is situated just east of

Miami an impressive RH gradient can be seen cutting through central Florida and along the western coast. However, only one tornado is incorporated within the gradient while the other two remain under a much more saturated environment. At 400 hPa the RH gradient retains its strength and pushes south along the southern most tornadoes to be located on the southern edge of the gradient but once again none of the three tornadoes are located under the strongest portion of the RH gradient. Lower at 500 hPa the RH gradient relaxes quite a bit leaving only one tornado under the gradient while the other two remain under a region where the RH values are above 80%. Finally at 700 hPa the

RH gradient retreats far to the west leaving most of Florida extremely saturated. At this time the RH across much of Florida is above 70%. The small sample size during this time proves it difficult to say with confidence that the RH gradient accurately pinpointed the outbreak region as it was only able to pinpoint one of the tornadoes. However, observed soundings from Jacksonville and Miami (figure 104 and 105) do indeed show that the gradient in RH was present allowing for the possibility that the RH gradient was able to shift far enough south in between model runs to incorporate the two tornadoes on the southern edge of the RH gradient.

The bulk of the tornadoes associated with Hurricane Jeanne occurred after 1800

UTC the same day when seven tornadoes touched down across Florida and southern

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Georgia. Figure 106 shows that the majority of the tornadoes were located near the

Jacksonville area. At 300 hPa a strong RH gradient can be seen across central Georgia incorporating one of the tornadoes however, the majority of the tornadoes occur well to the south where RH values are above 80%. The same thing can be seen at 400 hPa except the RH gradient pushes south incorporating the second Georgia tornado. Still the majority of the tornadoes are located under a saturated environment at this level. At 500 hPa the

RH gradient pushed even further south yet still remains too far north to incorporate the

Florida tornadoes. By 700 hPa the RH gradient seen in the upper levels is nonexistent with RH values near the Florida tornadoes between 80-90% while the two Georgia tornadoes have RH values between 60-70%. Observed soundings for Charleston, South

Carolina and Jacksonville, Florida (107 and 108) help confirm the RH gradient seen in the reanalysis data was indeed present at the time. Unfortunately, while the RH gradient lined up very well especially at 400 hPa for the Georgia tornadoes the RH gradient failed to come close to the Florida tornadoes which made up the bulk of the tornadoes associated with this particular outbreak.

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Figure 102. Best track positions for Hurricane Jeanne, 13-28 September 2004.

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Figure 103. Relative humidity for 300, 400, 500, and 700 hPa for 0000 UTC on September 26. Images created using the European Centre for Medium-Range Weather Forecasts ERA-Interim reanalysis data within Matlab. Warmer colors indicate dry air while cooler colors indicate moist air. Black star indicates the location of the tropical cyclone at the current time. Dots represent the location of the various tornadoes that spawned at that time.

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Figure 104. Atmospheric profile sounding for Jacksonville, Florida taken at 0000 UTC on September 26th. Image was taken from the University of Wyoming Department of Atmospheric Science sounding page.

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Figure 105. Atmospheric profile sounding for Miami, Florida taken at 0000 UTC on September 26th. Image was taken from the University of Wyoming Department of Atmospheric Science sounding page.

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Figure 106. Relative humidity for 300, 400, 500, and 700 hPa for 1800 UTC on September 26. Images created using the European Centre for Medium-Range Weather Forecasts ERA-Interim reanalysis data within Matlab. Warmer colors indicate dry air while cooler colors indicate moist air. Black star indicates the location of the tropical cyclone at the current time. Dots represent the location of the various tornadoes that spawned at that time.

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Figure 107. Atmospheric profile sounding for Charleston, South Carolina taken at 1800 UTC on September 26th. Image was taken from the University of Wyoming Department of Atmospheric Science sounding page.

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Figure 108. Atmospheric profile sounding for Jacksonville, Florida taken at 1800 UTC on September 26th. Image was taken from the University of Wyoming Department of Atmospheric Science sounding page.

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3.18 Katrina (2005)

Hurricane was the costliest and one of the most deadly hurricanes to hit the

United States. The massive hurricane carved a path through Florida and eventually the

Gulf Coast inflicting unprecedented damage and loss of life. Katrina originally developed when a tropical wave moving off the coast of Africa merged with a midlevel remnant circulation from tropical depression ten producing a large amount of thunderstorms just north of Puerto Rico. As the system moved west-northwest through Hispaniola and the

Turk and Caicos Islands the environmental shear present was weak enough for the system to develop into a tropical depression by 1800 UTC on August 23rd. The cyclone strengthened as it moved through the Bahamas becoming a tropical storm by 1200 UTC on August 24. A large upper level ridge began to steer the cyclone west were it deepened and made landfall as a Category 1 hurricane with 70 kt winds near the Miami-Dade and

Broward County line at 2230 UTC in August 25. Vertical wind shear helped weaken the cyclone as it moved across Florida however; the eye remained intact as it reemerging into the Gulf of Mexico. Once over the Gulf, Katrina quickly regained hurricane status as weak shear allowed Katrina to go through two periods of rapid intensification. Katrina grew to a Category 3 hurricane by 1200 UTC on August 27th. During an eye wall replacement cycle Katrina doubled in size and tropical storm forced winds were observed as far as 140 n mi away from the center. By 0000 UTC on August 28th Katrina had reached Category 5 strength with a peak intensity of 150 kt winds 170 n mi south of the

Mississippi River Delta. By this time tropical storm force winds were observed as far out as 200 n mi from the center. This rapid growth however, was short lived as NHC noted a

191 rapid weakening as part of the eye wall began to erode. Katrina turned north and made landfall as a category 3 storm at 1110 UTC on August 29th near Buras, Louisiana. Katrina began to weaken rapidly as a result of dry air, cooler SST’s, vertical shear, and land interactions. Katrina’s track and intensity can be seen in figure 109.

Katrina caused catastrophic storm surge along the Gulf Coast that completely leveled homes and businesses and inundated many communities including New Orleans.

FEMA and NHC report that storm surge reached as high as 24-28 ft along the Mississippi

Coast. The eastern part of the Mississippi coast saw storm surge around 17-22 ft. New

Orleans saw storm surge reach as high as 12-16 ft. The strength of the surge caused levees to fail while many others where overtopped by flood water. By the end of the storm 80% of New Orleans was underwater and remained flooded for 43 more days. The devastating storm surge was due to Katrina’s tremendous size. A total of 44 tornadoes across four states were reported after Katrina made landfall. The 20 tornadoes that occurred in Georgia were the most ever for a single day in the month of August. The region took quite an economic hit as well as the Hurricane crippled oil production and caused many oil rigs and refineries to shut down either as a precaution or due to damage.

Tourism was also effect as many seaside communities were completely leveled. In the end Hurricane Katrina is responsible for 41.1 billion dollars in damages.

The first four tornadoes spawned shortly after 1800 UTC on August 28th. Figure

110 indicates that the tornadoes were located in southern Alabama and the western

Florida Panhandle. Figure 110 also shows a strong RH gradient located all along the coast especially at 300 and 400 hPa. At these two levels the strongest portion of the RH

192 gradient is located just north of where the three Alabama tornadoes form. Only one tornado forms where the RH is around 50% while the others occur with RH values greater than 70%. At 500 the RH gradient weakens and retreats north. As a result the strongest portion of the RH gradient is now located away from the coast where the tornadoes are located. At this time all four tornadoes occur where the RH values are around 80%. Finally at 700hPa, there is no RH gradient in the region leaving much of the

Gulf Coast saturated with RH values near 70% where all four tornadoes are located. 1800

UTC observed soundings for Tallahassee and Slidell Muni were used to verify the location of the RH gradient. Tallahassee was used because it was located far enough east where the reanalysis data indicates that the environment over Tallahassee was saturated though out the entire column. Figure 111 shows that this is indeed correct matching what was seen in the reanalysis data. Slidell Muni, Louisiana was used as it was located under the dry air intrusion especially at 300 and 400 hPa. Looking at figure 112 one can see that the lower levels remain fairly saturated but becomes unsaturated between 400 and 300 hPa which is what is seen in figure 110. This verifies that there was indeed an RH gradient present between eastern Louisiana and western Florida. With the RH gradient verified as being present in the region it still failed to pinpoint the location of the tornadoes.

The next 17 tornadoes occurred after 1200 UTC on August 29th. Figure 113 illustrates that the majority of the tornadoes were located over central Mississippi with a handful of others scattered across western Florida and Alabama. At 300 hPa there is a small pocket of dry air located just south of the Alabama coast producing a very weak

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RH gradient. This gradient only incorporates five tornadoes and they occur near the northern edge. At 300 hPa there is no tight RH gradient seen in past storms or in the findings by Curtis. The rest of the tornadoes at 300 hPa occur where the RH is well above

80-90%. At 400 hPa there is a tight RH gradient south if the Louisiana coastline well removed from the tornado outbreak region. At 400 hPa the tornadoes form where the RH increases from 60-90% however, the RH gradient is weak. Lower at 500 hPa we see a large pocket of dry air beginning to wrap around the cyclone towards the east. As a result a tighter RH gradient is seen over southern Alabama/western Florida then what was seen at 300 hPa. At this time three to four tornadoes are located within the tightest portion of the RH gradient where the RH increases from 50-80%. Even with this gradient the majority of the tornadoes were located much further away towards the northwest. Finally at 700 hPa we see the environment over the outbreak region become drier however there is no significant RH gradient over the outbreak region. Observed sounding for Jackson,

Mississippi was used to verify the saturated environment seen in the reanalysis data.

Figure 114 clearly indicates that the environment near where the majority of the tornadoes occurred remained saturated throughout the entire column. A second observed sounding for Tallahassee (not shown) also help verify the dry air seen to the east.

The third outbreak occurred between 1800 UTC on August 29th and 0000 UTC on

August 30th. Figure 115 shows the corresponding RH values for 1800 UTC as well as tornado locations. Due to Katrina’s tremendous size the majority of the tornadoes that occurred at this time were located over northern Georgia while the center of rotation was located over southern Mississippi. At 300 hPa there is a significantly strong RH gradient

194 seen over southern Georgia and northern Florida. However, the gradient is located well away from the outbreak region leaving all except one tornado in an area where the RH is

90%. At 400 hPa the RH gradient retreats east while the environment over the outbreak region as a whole becomes drier. Even with these drier conditions aloft there is no strong

RH gradient present. There is a weak to moderate RH gradient over northern Georgia that does incorporate a few tornadoes however, the gradient is much weaker compared to the gradients seen in the findings by Curtis. At 500 hPa the environment becomes even less saturated but the RH values remain constant at 60% throughout much of the outbreak region. Similar to what was seen at 400 hPa there is a weak RH gradient west of the

Alabama/Georgia border that does manage to incorporate some of the western tornadoes.

With that said however, the RH gradient still fails to pinpoint the majority of the tornadoes that spawned at this time at both 500 and 400 hPa. Finally at 700 hPa the majority of the southeast remains saturated with much of the outbreak region located where the RH values remain constant near 70%.

The final set of tornadoes included in this study occurred right after 0000 UTC on

August 30th. All five tornadoes spawned over northern Georgia as seen in figure 116. At

300 hPa there is a strong RH gradient over southeast Georgia but, all five tornadoes occur to far north to be incorporated by the gradient. At 400 hPa the strong RH gradient is located along the Gulf Coast leaving the tornado outbreak region under an area where the

RH remains constant around 90%. Lower at 500 hPa the environment over northern

Georgia becomes less saturated allowing a very weak RH gradient to develop over the region. The tornadoes are located where the RH increases form about 70-80% however,

195 the strength of this RH gradient is nowhere near the strength seen by Curtis or purposed by this paper. Finally at 700 hPa we have an environment that is very saturated with RH values around 80% and no strong RH gradient in the vicinity of the outbreak region.

Observed 0000 UTC sounding for Peachtree City, Georgia was used to verify that the environment remained saturated through all four levels as seen in the reanalysis data.

Figure 117 does indeed show a saturated environment through the column with very weak dry air pockets scattered throughout the lower levels. Overall there were no strong

RH gradients in any of the four separate outbreaks mentioned above that was able to pinpoint the location of any of the tornado outbreaks discusses. Katrina was a significant storm to analyze because of its strength and size of the tornado outbreak similar to storms analyzed by Curtis. Even with these similarities Katrina still failed to show that the tornado outbreaks lined up with gradients in RH.

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Figure 109. Best track positions for Hurricane Katrina, 23-30 August 2005.

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Figure 110. Relative humidity for 300, 400, 500, and 700 hPa for 1800 UTC on 28 August. Images created using the European Centre for Medium-Range Weather Forecasts ERA-Interim reanalysis data within Matlab. Warmer colors indicate dry air while cooler colors indicate moist air. Black star indicates the location of the tropical cyclone at the current time. Dots represent the location of the various tornadoes that spawned at that time.

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Figure 111. Atmospheric profile sounding for Tallahassee, Florida taken at 1800 UTC on August 28th. Image was taken from the University of Wyoming Department of Atmospheric Science sounding page.

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Figure 112. Atmospheric profile sounding for Slidell Muni, Louisiana taken at 1800 UTC on August 28th. Image was taken from the University of Wyoming Department of Atmospheric Science sounding page.

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Figure 113. Relative humidity for 300, 400, 500, and 700 hPa for 1200 UTC on 29 August. Images created using the European Centre for Medium-Range Weather Forecasts ERA-Interim reanalysis data within Matlab. Warmer colors indicate dry air while cooler colors indicate moist air. Black star indicates the location of the tropical cyclone at the current time. Dots represent the location of the various tornadoes that spawned at that time.

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Figure 114. Atmospheric profile sounding for Jackson, Mississippi taken at 1200 UTC on August 29th. Image was taken from the University of Wyoming Department of Atmospheric Science sounding page.

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Figure 115. Relative humidity for 300, 400, 500, and 700 hPa for 1800 UTC on 29 August. Images created using the European Centre for Medium-Range Weather Forecasts ERA-Interim reanalysis data within Matlab. Warmer colors indicate dry air while cooler colors indicate moist air. Black star indicates the location of the tropical cyclone at the current time. Dots represent the location of the various tornadoes that spawned at that time.

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Figure 116. Relative humidity for 300, 400, 500, and 700 hPa for 0000 UTC on 30 August. Images created using the European Centre for Medium-Range Weather Forecasts ERA-Interim reanalysis data within Matlab. Warmer colors indicate dry air while cooler colors indicate moist air. Black star indicates the location of the tropical cyclone at the current time. Dots represent the location of the various tornadoes that spawned at that time.

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Figure 117. Atmospheric profile sounding for Peachtree City, Georgia taken at 0000 UTC on August 30th. Image was taken from the University of Wyoming Department of Atmospheric Science sounding page.

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3.19 Lee (2011)

Lee originally developed from an active tropical wave that moved off the coast of

Africa on August 18th. The wave entered a region with strong vertical shear and dry air which prevented any organization. The tropical wave split and the southern portion continued to move west where it deepen and grew in size. Once a closed circulation became apparent NHC upgraded the system to a tropical depression at 0000 UTC on

September 2nd. 12 hours later the depression shifted to the north and was upgraded to tropical storm strength. Vertical wind shear of about 20 kts and an upper level cyclone nearby were unable to weaken Tropical Storm Lee and as a result it gradually strengthened as it moved north. Lee stalled just off the coast of the coast of Louisiana where a dry air intrusion helped weaken the convection. As a result Lee made landfall as a subtropical cyclone at 1030 UTC near Intracoastal City, Louisiana. Tropical Storm

Lee’s track and intensity can be seen in figure 118.

Moderate storm surge was reported along much of the Gulf Coast with storm surge around 3-6 feet. This resulted in freshwater flooding as well as more than 150 houses being inundated. Much of southern Louisiana, Mississippi, and Alabama saw rainfall reports around 10-15 inches. NHC reports that a total of 46 tornadoes were reported as a result of Lee and its remnants. The majority of the tornadoes occurred when

Lee was well inland however, 17 tornadoes occurred with in the 24 hrs before or after landfall across southern Louisiana, Mississippi, Alabama, and the Florida panhandle. The remnants of Lee wreaked havoc on the Mid-Atlantic States all the way to New England who were still recovering from the devastating rainfall associated with Hurricane Irene

206 just a few weeks before. Initial reports indicate that Lee produced an estimated 315 million dollars in damages.

The first four tornadoes occurred shortly after 1800 UTC on September 3rd.

Figure 119 shows that the tornadoes are scattered across southern Louisiana, Mississippi, and Alabama. At 300 hPa the tropical cyclone is riding along a tight RH gradient just west of a large pocket of dry air that is beginning to wrap around the cyclone. At this time only one tornado near New Orleans is incorporated within the tight RH gradient.

The other three occurred just outside the northern edge of the gradient. While not perfect the RH gradient was much closer at pinpointing tornado location then previous storms examined. At 400 hPa the RH gradient weakens quite a bit and only incorporates one tornado similar to what was seen at 300 hPa. By 500 hPa the environment at this level is very saturated with only a minor RH gradient much weaker then what was seen by Curtis and other gradients within this study. No tornadoes occur where the RH is less than 70%.

Finally at 700 hPa the environment becomes even more saturated and as a result the majority of the tornadoes occur where the RH is above 90%. Observed soundings for

Lake Charles and Slidell Muni (not shown) do show the environment becoming less saturated as one moves west from Lake Charles. This matches what is shown in the reanalysis data.

The following six tornadoes occurred shortly after 0600 UTC on September 4th.

Figure 120 shows that the majority of the tornadoes were located over southern

Mississippi/Alabama. Again we see a large dry air intrusion at 300, 400, and 500 hPa located east of the tropical cyclone. At 300 hPa there is a very tight RH gradient located

207 along the southern Louisiana/Mississippi border. However, the gradient is located far enough to the west to only incorporate one tornado. The remaining five occur where the

RH is 80% or higher. At 400 hPa the RH gradient pushes northeast and incorporates four tornadoes over the strongest portion of the gradient where the RH values quickly increase from 30-70%. At 500 hPa the RH gradient relaxes and as a result only three tornadoes are located under the strongest portion of the RH gradient. The RH gradient only increases from 50-70% which is much weaker then what was seen at 400 hPa. Finally at 700 hPa the environment becomes saturated with no strong RH gradient in the region. At this level the tornadoes all occurred where the RH is 70% or higher. Soundings for 0000 and

1200 UTC taken on September 4th for Slidell Muni (figure 121 and 122) shows how the environment especially at the upper levels becomes less saturated as multiple dry air intrusions can be seen throughout the sounding. This agrees with the reanalysis data that shows the strong RH gradient being present east of Slidell Muni. This allows one to make the statement that the RH gradient at 400 and even 500 hPa did a fair job at pinpointing the tornado outbreak with confidence.

The final outbreak examined associated with Lee occurred after 1800 UTC on

September 4th when seven tornadoes spawned. Figure 123 shows that the majority of the tornadoes occurred over southern Mississippi. At 300 hPa there is a dry air pocket working its way north towards southeast Louisiana. As a result only two tornadoes fall under the strongest portion of the RH gradient. The other five tornadoes occur when the

RH is 70% or higher. At 400 hPa the dry air intrusion surges north increasing the area covered by the strongest portion of the RH gradient. Five of the seven tornadoes are

208 located under the strongest portion of the RH gradient where values increase rapidly from

30-70%. At 500 hPa the RH gradient strengthens as dry air continues to move north just off the coast of southern Mississippi. The RH gradient again incorporates five tornadoes where the RH values increase from 20-60% over the outbreak region. Finally at 700 hPa the environment is totally saturated where RH values never dip below 80% over the outbreak region. Lack of soundings near the RH gradient makes it difficult to verify the dry air intrusions shown by the reanalysis data. However, the 1200 UTC sounding for

Slidell Muni does indicate that there is lots of dry air scattered throughout the environment. This would conclude that that RH gradient did an exceptional job at pinpointing the tornadoes location. The RH gradient at 400 and 500 hPa were spot on at locating were five out of the seven tornadoes would spawn. This is one of the few example where the RH gradient was so accurate matching the findings by Curtis.

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Figure 118. Best track positions for Tropical Storm Lee, 2-5 September 2011. Track during the extratropical stage is partially based on analyses from the NOAA Hydrometeorological Prediction Center.

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Figure 119. Relative humidity for 300, 400, 500, and 700 hPa for 1800 UTC on 3 September. Images created using the European Centre for Medium-Range Weather Forecasts ERA-Interim reanalysis data within Matlab. Warmer colors indicate dry air while cooler colors indicate moist air. Black star indicates the location of the tropical cyclone at the current time. Dots represent the location of the various tornadoes that spawned at that time.

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Figure 120. Relative humidity for 300, 400, 500, and 700 hPa for 0600 UTC on 4 September. Images created using the European Centre for Medium-Range Weather Forecasts ERA-Interim reanalysis data within Matlab. Warmer colors indicate dry air while cooler colors indicate moist air. Black star indicates the location of the tropical cyclone at the current time. Dots represent the location of the various tornadoes that spawned at that time.

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Figure 121. Atmospheric profile sounding for Slidell Muni, Louisiana taken at 0000 UTC on September 4th. Image was taken from the University of Wyoming Department of Atmospheric Science sounding page.

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Figure 122. Atmospheric profile sounding for Slidell Muni, Louisiana taken at 1200 UTC on September 4th. Image was taken from the University of Wyoming Department of Atmospheric Science sounding page.

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Figure 123. Relative humidity for 300, 400, 500, and 700 hPa for 1800 UTC on 4 September. Images created using the European Centre for Medium-Range Weather Forecasts ERA-Interim reanalysis data within Matlab. Warmer colors indicate dry air while cooler colors indicate moist air. Black star indicates the location of the tropical cyclone at the current time. Dots represent the location of the various tornadoes that spawned at that time.

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3.20 Lili (2002)

Lili originated from a tropical wave off the west coast of Africa on September

16th. NHC upgraded the system to a tropical depression when convection became more organized. The system continued to move west steered by an upper level ridge over the

Atlantic. Eventually the system encountered an area of enhanced vertical wind shear disrupting the organized convection causing the storm to be demoted to an open tropical wave. As the wave approached Jamaica the wave redeveloped a closed circulation and eventually reached hurricane strength on August 30th. Lili shifted north and made landfall on the Louisiana coastline on September 3rd. Hurricane Lili’s track and intensity can be seen in figure 124. The combination of heavy rainfall and moderate storm surged caused levees to fail in Louisiana. Wind spread wind damage was also reported. A total of 25 tornadoes were reported throughout Louisiana and Mississippi. The majority were F 0 however a few made it to F 1 strength.

The first set of tornadoes occurred after 1200 UTC on October 3rd when 17 tornadoes spawned across southern Louisiana and Mississippi. Figure 125 shows RH values for that time as well as the location of all 17 tornadoes. At 300 hPa on can identify two very strong RH gradients one just off the Louisiana coastline and the other located through Alabama. However, the two RH gradients are located too far away to incorporate any of the tornadoes. As a result the vast majority of the tornadoes occur where the RH remains constant at around 90%. The same scenario can be seen in at 400 hPa. While the tropical cyclone was able to wrap drier air further north at this level the RH gradient still remains too far south to incorporate any of the tornadoes. In fact only one tornado forms

216 where the RH is below 80%. Lower at 500 hPa the strong RH gradient seen at 300 and

400 hPa weakens and retreats off shore once again leaving only one tornado that spawns where the RH is below 80%. Finally at 700 hPa there is no RH gradient seen anywhere near the outbreak region. All 17 tornadoes at this level occur where the RH is above 80%.

The observed sounding from Lake Charles, Louisiana taken at 1200 UTC helps demonstrate how saturated the environment over Louisiana was at the time the tornadoes occurred. Figure 126 shows that the temperature profile follows the moist adiabatic line throughout the entire column indicating that the environment was indeed very saturated matching what was seen in the reanalysis data. Overall the RH gradient did a poor job at pinpointing the location of the tornadoes associated with the first set of tornadoes.

The final eight tornadoes occurred between 1800 UTC on October 3rd and 0000

UTC on October 4th. Figure 127 shows RH values as well as the location of the tornadoes which were located across central Louisiana and southern Mississippi. At 300 hPa there are two strong RH gradients present however, they are located to far south and west of where the tornadoes were located. All but two tornadoes occurred where the RH was

80% or higher. For the remaining two tornadoes one occurred where the RH was 70% and the other occurred where the RH was 60%. At 400 hPa the RH gradients weak significantly and are still located too far away to incorporate the majority of the tornadoes at this levels. The two southern Mississippi tornadoes do occur where the RH fluctuates between 50-60% however; the strongest portion of the gradient is located farther east.

Lower at 500 hPa we begin to see the RH gradient begin to incorporate many of the tornadoes. A large dry air intrusion can be seen beginning to wrap itself around the

217 cyclone towards the northeast. As a result all eight tornadoes are located within the RH gradient with five of them being located along the strongest portion of the RH gradient similar to what was shown by Curtis. At this time the RH values increase greatly from

30-80% over the five easternmost tornadoes. The remaining three tornadoes to the west occurred under the gradient but they are removed from the strongest portion. The tornadoes proximity to the core of the cyclone could have been what kept that region saturated. At 700 hPa there are no identifiably RH gradients present around the outbreak regions and as a result the RH values remain constant between 80-90%. The RH gradient at 500 hPa accurately pinpointed five of the eight tornadoes matching the findings by

Curtis. Unfortunately due to lack of observed soundings especially around New Orleans it is difficult to verify the presence of the dry air intrusion seen at 500 hPa.

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Figure 124. Best track positions for Hurricane Lili, 21 September - 4 October 2002.

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Figure 125. Relative humidity for 300, 400, 500, and 700 hPa for 1200 UTC on 03 October. Images created using the European Centre for Medium-Range Weather Forecasts ERA-Interim reanalysis data within Matlab. Warmer colors indicate dry air while cooler colors indicate moist air. Black star indicates the location of the tropical cyclone at the current time. Dots represent the location of the various tornadoes that spawned at that time.

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Figure 126. Atmospheric profile sounding for Lake Charles, Louisiana taken at 1200 UTC on October 3rd. Image was taken from the University of Wyoming Department of Atmospheric Science sounding page.

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Figure 127. Relative humidity for 300, 400, 500, and 700 hPa for 1800 UTC on 03 October. Images created using the European Centre for Medium-Range Weather Forecasts ERA-Interim reanalysis data within Matlab. Warmer colors indicate dry air while cooler colors indicate moist air. Black star indicates the location of the tropical cyclone at the current time. Dots represent the location of the various tornadoes that spawned at that time.

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3.21 Rita (2005)

Hurricane Rita was a destructive storm that reached Category 5 strength in the

Gulf of Mexico before wreaking havoc on the Gulf Coast. Rita originated from the interaction between a tropical wave and a cold front. The tropical wave produced little convection as it moved across the Atlantic. Meanwhile, a cold front moving across the

Atlantic stalled and the southernmost piece began to lose definition eventually becoming a remnant surface trough which became detached from the front as it continued eastward.

Unlike the tropical wave, the trough produced a large area of convective activity. The two systems merged and organized forming a tropical depression at 0000 UTC on September

18th near the Turks and Caicos. Vertical wind shear prevented the system from organizing and intensifying as the system became asymmetric. As the shear began to weaken the system grew in strength and reached Category 2 status when the center passed 40 n mi south of Key West by 1800 UTC on September 20th. It wasn’t until Rita reached the warm waters of the Gulf that the system quickly intensified and in less than

36 hours Rita had reached Category 5 status. Rita reached a peak intensity of 155 kt winds by 0300 UC on September 22nd. This was short lived however, as Rita’s inner eye wall began to weaken which lead to an eye wall replacement cycle which caused Rita to double and size. Rita continued to weaken until landfall near Johnson’s Bayou as a

Category 3 hurricane at 0740 UTC on September 24th. Rita’s track and intensity can be seen in figure 128.

Due to Rita’s large size devastating storm surge was felt across the Gulf Coast.

Louisiana was the hardest hit especially areas in the southwestern part of the state where

223 entire communities were leveled. NHC and FEMA report that storm surged reached as high as 15 feet and flooded areas as far as 25 n mi from the coast. Southeastern Louisiana which was still recovering from the destruction caused by Hurricane Katrina a month before saw storm surge as high as 4-7 ft. Although the flooding in southeast Louisiana were nowhere near as bad as Katrina the extra flood water prolong recovery efforts in impacted communities. A total of 90 tornadoes were reported in association with Rita.

For the purpose of this paper 53 tornadoes were reported during the 24 hrs before or after landfall across Louisiana, Mississippi, and Arkansas.

The first seven tornadoes with Hurricane Rita occurred near 1200 UTC on

September 24th. Figure 129 shows that the tornadoes were located in southeastern

Arkansas as well as southwest Mississippi. RH values from the reanalysis data also included in the image show that there are multiple RH gradients present at each level analyzed. At both 300 and 400 hPa there are strong RH gradients located towards the southeast and northwest of the outbreak region. However, all the tornadoes are located in between where the strongest portion of the gradient is located. As a result, all the tornadoes are located where the RH remains constant between 80-90% at the two upper most levels analyzed. At 500 hPa the outbreak region becomes less saturated as the dry air intrusion to the east is able to push west. The tornadoes still remain away from the tightest portion of the gradient under a region where the RH remained constant around

70-80%. Finally at 700 hPa the dry air retreats south however, the tightest RH gradient during this time is seen over the outbreak region. RH values increase from 50-90% over where the tornadoes occurred. Observed 1200 UTC soundings from Shreveport,

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Louisiana and Jackson Mississippi were used to help verify the RH gradient. Figure 130 shows the sounding for Shreveport, Louisiana while figure 131 is the sounding for

Jackson, Mississippi. Looking at the soundings the environment in the upper levels remains fairly saturated as you move west to east. However, at the lower levels one can see the influence of the dry air intrusion especially below 500 hPa. The environment over

Shreveport remains saturated but as one approaches Jackson multiple pockets of dry air are seen matching what was displayed using the reanalysis data. As a result the RH gradient seen at 700 hPa was able to accurately pinpoint the tornado outbreak region.

The largest outbreak analyzed during Hurricane Rita occurred just after 1800

UTC on September 24th when 34 tornadoes were confirmed across Arkansas, Mississippi, and Louisiana as seen in figure 132. Using the same figure RH values at 300 hPa indicate that the level was completely saturated at the time across the entire outbreak region. Only two tornadoes occur where the RH is less than 90% at 300 hPa. At 400 hPa we see more of the same as 30 of the 34 tornadoes occurs where the RH is 90% or higher even though the dry air intrusion made a strong push northward. The opposite is seen at 500 hPa where strong RH gradients encompass the entire outbreak region. At 500 hPa it is clear that there are two strong RH gradients to the north and east which are co-located over 25 of the 34 storms. The seven northern most tornadoes are located where the RH increases from 50-90% over central Arkansas. The tornadoes over western Mississippi fall under a

RH gradient that rapidly increases from 40-80% over a very small distance. 1800 UTC sounding for Jackson, Mississippi helps verify the dry air present seen in figure 133. The

1800 Sounding for Little Rock, Arkansas (not shown) displays similar results. Finally at

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700 hPa the environment becomes more saturated however, a moderate RH gradient over western Mississippi extending to extreme southeastern Arkansas can be seen incorporating a large number of tornadoes where the RH increases from about 50-90% over a larger distance compared to the gradient seen at 500 hPa. Overall the RH gradient at 500 and 700 hPa were able to accurately pinpoint the location of the tornado outbreaks.

This was one of the few examples that were able to match the findings by Curtis with high confidence.

The third outbreak occurred after 0000 UTC on September 25th. At this time seven tornadoes spawned near the Mississippi River in southeast Arkansas, western

Mississippi, and northeast Louisiana seen in figure 134. RH values on the same image show that at 300 hPa there is a very strong RH gradient that incorporates the majority of the tornadoes where the RH values increase from 30-70%. 0000 UTC soundings from

Slidell Muni and Little Rock help show the extent of the dry air intrusion at 300 hPa.

Figure 135 and 136 show the 0000 UTC soundings for Slidell Muni and Little Rock respectively. It’s clear that the upper levels are extremely dry over southern Louisiana and as you move north towards Little Rock the environment becomes extremely saturated. This concludes there must be some sort of RH gradient present which matches what is shown using the reanalysis data. As a result, 300 hPa does a fair job at locating the outbreak region using the RH gradient. Unfortunately, this is the only level were we see the RH gradient line up with the outbreak region. At 400 and 500 hPa there are strong

RH gradients that encompass Hurricane Rita and the associated tornado outbreak region.

However, the strongest portions of said gradients are located away from the outbreak

226 region. At these two levels the tornadoes all occur where the RH is constantly at 90%.

Finally at 700 hPa the entire region becomes more saturated and once again the tornadoes occurred where the RH remains constant around 90%.

The last outbreak analyzed occurred just after 0600 UTC on September 25th. At this time five tornadoes spawned across Louisiana and Mississippi as seen in figure 137.

This image also demonstrates one of the best examples of the RH gradient being located right over the tornado outbreak region. At both 300 and 400 hPa there is a strong RH gradient that runs through northern Louisiana/southwestern Mississippi. Here the RH values increase from about 30-70% directly over where the tornadoes occurred matching the findings by Curtis. While no 0600 soundings were launched that could directly confirm the placement of the RH gradient 0000 and 1200 UTC soundings for locations such as Slidell Muni, Shreveport, and Little Rock (not shown) all support the notion that the dry air indicated by the reanalysis data was indeed present at the time. At 500 hPa the

RH gradient retreats south leaving much of the tornado region north of the strongest portions of the gradient where the RH hovers between 80-90%. Finally at 700 hPa there is very little dry air present near the vicinity of the outbreak region where the RH remains steady at about 90%. Overall, the RH gradient lined up perfectly with the outbreak region at 300 and 400 hPa providing one of the best examples that supports the findings by

Curtis.

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Figure 128. Best track positions for Hurricane Rita, 18-26 September 2005.

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Figure 129. Relative humidity for 300, 400, 500, and 700 hPa for 1200 UTC on 24 September. Images created using the European Centre for Medium-Range Weather Forecasts ERA-Interim reanalysis data within Matlab. Warmer colors indicate dry air while cooler colors indicate moist air. Black star indicates the location of the tropical cyclone at the current time. Dots represent the location of the various tornadoes that spawned at that time.

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Figure 130. Atmospheric profile sounding for Shreveport, Louisiana taken at 1200 UTC on September 24. Image was taken from the University of Wyoming Department of Atmospheric Science sounding page.

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Figure 131. Atmospheric profile sounding for Jackson, Mississippi taken at 1200 UTC on September 24. Image was taken from the University of Wyoming Department of Atmospheric Science sounding page.

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Figure 132. Relative humidity for 300, 400, 500, and 700 hPa for 1800 UTC on 24 September. Images created using the European Centre for Medium-Range Weather Forecasts ERA-Interim reanalysis data within Matlab. Warmer colors indicate dry air while cooler colors indicate moist air. Black star indicates the location of the tropical cyclone at the current time. Dots represent the location of the various tornadoes that spawned at that time.

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Figure 133. Atmospheric profile sounding for Jackson, Mississippi taken at 1800 UTC on September 24. Image was taken from the University of Wyoming Department of Atmospheric Science sounding page.

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Figure 134. Relative humidity for 300, 400, 500, and 700 hPa for 0000 UTC on 25 September. Images created using the European Centre for Medium-Range Weather Forecasts ERA-Interim reanalysis data within Matlab. Warmer colors indicate dry air while cooler colors indicate moist air. Black star indicates the location of the tropical cyclone at the current time. Dots represent the location of the various tornadoes that spawned at that time.

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Figure 135. Atmospheric profile sounding for Slidell Muni, Louisiana taken at 0000 UTC on September 25. Image was taken from the University of Wyoming Department of Atmospheric Science sounding page.

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Figure 136. Atmospheric profile sounding for Little Rock, Arkansas taken at 0000 UTC on September 25. Image was taken from the University of Wyoming Department of Atmospheric Science sounding page.

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Figure 137. Relative humidity for 300, 400, 500, and 700 hPa for 0600 UTC on 25 September. Images created using the European Centre for Medium-Range Weather Forecasts ERA-Interim reanalysis data within Matlab. Warmer colors indicate dry air while cooler colors indicate moist air. Black star indicates the location of the tropical cyclone at the current time. Dots represent the location of the various tornadoes that spawned at that time.

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3.22 Wilma (2005)

Wilma originated from a combination of tropical waves merging with an extra tropical cyclone near Jamaica. These features were quickly able to organize creating a well-defined surface circulation allowing NHC to designate it as a tropical depression by

1800 UTC on October 15th. Weak steering caused the tropical depression to drift westward strengthening only slightly to a tropical storm by 0600 UTC on October 17th.

48 hours later Tropical Storm Rita went through a significant period of unprecedented intensification reaching Category 5 strength by 0600 UTC on October 19th. Hurricane

Wilma reached peak intensity by 1200 UTC the same day with speeds of 160 kts. During this time NHC reported that the diameter of the eye shrank to 2 n mi making it the smallest eye on record. An eye wall replacement cycle weakened Wilma as the eye expanded to 40 n mi in diameter. Wilma shifted north and impacted the Yucatan

Peninsula with Category 4 winds. A strong upper level dropped helped shift Wilma to the northeast but also provided wind shear which helped prevent rapid intensification.

However, Hurricane Rita still made landfall as a powerful Category 3 storm with estimated winds near 105 kts near Cape Romano by 1030 UTC on October 24th. Rita’s track and intensity can be seen in figure 138. Rita quickly move through the Florida peninsula and as a result rainfall amounts ranged anywhere from 3 to 7 inches. However,

Rita did produce about seven tornadoes across the state of Florida. All tornadoes were F 0 and produced little to no damage.

The first three tornadoes spawned shortly after 1800 UTC on October 23rd. Figure

139 indicates that the tornadoes were located just east of Tampa while the core of the

238 system was located well to the southwest of Key West. RH values can also be on figure

139. At 300 hPa there is a strong RH gradient located right over the tornadoes along central Florida. The tornadoes are incorporated in an RH gradient that increases rapidly from 40% to 80%. Lower at 400 hPa the RH gradient remains in place however, the gradient is weaker with RH values increasing from 50% to 70%. Observed soundings from Tampa and Miami taken at 1800 UTC were used to verify the presence of the RH gradient seen in the upper levels. Figure 140 is the sounding for Tampa, Florida where there is a completely saturated environment throughout almost the entire column with drier air located near the surface. Figure 141 is the sounding for Miami, Florida taken at the same time. Looking at the Miami sounding one can see a large dry air intrusion located over the region especially between 500 and 200 hPa. Looking at the two soundings together one can clearly see that the upper levels do become less saturated as you move towards the southeast of Tampa matching what was seen in the reanalysis data.

At 500 hPa the RH gradient weakens further and moved off shore leaving the outbreak region under an area of constant RH near 50%. Finally at 700 hPa the majority of Florida for the most part remains saturated with RH values hovering between 60-80%. Overall, the RH gradient at 400 and especially 300 hPa was able to pinpoint the location of the tornado outbreak with tremendous accurately. However, the same cannot be said for the remaining four tornadoes.

The final four tornadoes spawned around 0600 UTC on October 24th. The four tornadoes were scattered throughout central and southern Florida as seen in Figure 142.

At 300 and 400 hPa the region over the tornadoes remains fairly saturated with no strong

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RH gradient in the area. There is drier air at both levels located towards the southeast just off shore of Miami. However, this dry air is located too far east to incorporate any tornadoes. The majority of the tornadoes at both levels occurred when the RH values were around 80-90%. Lower at 500 hPa the RH gradient to the east strengthens and begins to incorporate the two northern most tornadoes. At this time the RH gradient quickly increases from 50-70% over the small area the tornadoes occurred. The remaining tornadoes to the west still remain under 90% RH. At 700 hPa the RH gradient retreats once again leaving the tornadoes under a region where the RH remains around

80%. For the second set of tornadoes the RH gradient did not do so well at pinpointing the location of the tornadoes. Even though the RH gradient did match up with two of the tornadoes at 400 hPa confidence remains low since the RH gradient was not able to pick up on all the tornadoes that spawned during this time unlike what was seen in the first set of tornadoes mentioned above. The small sample size of tornadoes also makes the storm difficult to analyses and to finalize a result with confidence.

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Figure 138. Best track positions for Hurricane Wilma, October 2005. Track during the extratropical stage is partially based on analyses from the NOAA Ocean Prediction Center.

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Figure 139. Relative humidity for 300, 400, 500, and 700 hPa for 1800 UTC on 23 October. Images created using the European Centre for Medium-Range Weather Forecasts ERA-Interim reanalysis data within Matlab. Warmer colors indicate dry air while cooler colors indicate moist air. Black star indicates the location of the tropical cyclone at the current time. Dots represent the location of the various tornadoes that spawned at that time.

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Figure 140. Atmospheric profile sounding for Tampa, Florida taken at 1800 UTC on October 23. Image was taken from the University of Wyoming Department of Atmospheric Science sounding page.

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Figure 141. Atmospheric profile sounding for Miami, Florida taken at 1800 UTC on October 23. Image was taken from the University of Wyoming Department of Atmospheric Science sounding page.

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Figure 142. Relative humidity for 300, 400, 500, and 700 hPa for 0600 UTC on 24 October. Images created using the European Centre for Medium-Range Weather Forecasts ERA-Interim reanalysis data within Matlab. Warmer colors indicate dry air while cooler colors indicate moist air. Black star indicates the location of the tropical cyclone at the current time. Dots represent the location of the various tornadoes that spawned at that time.

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Chapter 4: Tornado Statistics

To further test the hypothesis that RH gradients aloft align with tornado outbreaks within land falling tropical cyclones, each cyclone discussed was separated into various groups. These groupings were based off of the total amount of tornadoes that were located under RH gradients for each tropical cyclone. As a result the 22 tropical cyclones included in this paper were separated into six different groups. Group 1 consisted of tropical cyclones that were deemed a “perfect miss” in which no tornadoes associated with each tropical cyclone was located under any RH gradients. Group 2 contained tropical cyclones in which 1-24% of the total amount of tornadoes was located under a RH gradient. Group 3 consisted of tropical cyclones that had 25-49% of tornadoes under an RH gradient. Group 4 contained tropical cyclones which had at least

50-74% of tornadoes under an RH gradient while group 5 contained tropical cyclones that had 75-99% of tornadoes under the RH gradient. Finally, Group 6 contained tropical cyclones which were deemed a “perfect hit” where all the tornadoes where located beneath an RH gradient. Table 2 contains a list of which of which tropical cyclone is associated with each group based on the criteria mentioned above.

Once the groupings were created various percentages were calculated such as the amount of pre-landfall outbreaks vs. post landfall as well as daytime vs. nighttime

246 outbreaks. A daytime outbreak is considered to have occurred between 1200 UTC and

0000 UTC. I went further and calculated the percentages of the amount of tornadoes that were actually located under the RH gradient between pre/post landfall and day/night outbreaks. Finally I looked at each outbreak to determine which level produced the most occurrences in which the RH gradient was located above the tornado outbreak region.

This allowed for further analysis to distinguish any patterns and similarities between tropical cyclones that could help support or disprove Curtis initial findings that were only briefly mentioned in the original paper.

Group 1 consisted of Tropical Storm Bill and Tropical Storm Fay (2008) which produced a total of 20 tornadoes across five different outbreak periods. These two tropical cyclones were placed into this group because 0% of the tornadoes were located under a RH gradient. In fact, all the levels across the five outbreak periods indicate that the environment throughout the entire column remained very saturated with little dry air in the area. 60% of the tornadoes occurred pre landfall vs. 40% occurring post landfall.

There was also a strong diurnal signal as 75% of the tornadoes occurred during the day.

Similar to the challenges faced by Curtis these results are comprised of a very small sample size. The strong diurnal cycle as well as the majority of tornadoes spawning pre landfall found in the data must be taken with caution as the introduction of another tropical cyclone could have easily skewed the data one way or the other. However, the fact that only two tropical cyclones failed to produce any tornadoes under an RH gradient indicates that the results moving forward in relation to my hypothesis seem promising.

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Group 2 consisted of Hurricane Gabrielle and Hurricane Irene which produced 21 tornadoes across 5 separate outbreak periods. These two tropical cyclones were placed in the group because 1-24% of the total tornadoes spawned from each storm were located under an RH gradient. Out of the 12 tornadoes associated with Hurricane Gabriella only one was located under an RH gradient. The same was seen with Hurricane Irene as only one out of nine tornadoes was located under an RH gradient. It is important to note that only one tornado from each of the two tropical cyclones included in this group were located under an RH gradient. As a result they could have easily been included into group

1 based on which reanalysis data is used. The two tornadoes mentioned where located right on the edge of their corresponding RH gradients based off of the ERA Interim reanalysis data set. A slight shift in the location of said RH gradient which is possible within other data sets could have changed these specific results completely. Moving forward a majority of the tornadoes spawned pre landfall with about 57% of the tornadoes occurring around this time. However, even though the majority of the tornadoes occurred before landfall the two tornadoes that did occur under the RH gradient spawned post landfall. As a result 18% of the post landfall tornadoes occurred under an RH gradient. Again the sample size is small so this value is skewed. This group also saw a reversal in the diurnal cycle seen in Group 1. 52% of the total tornadoes occurred during the daytime hours while 57% occurred at night. The biggest take away from this group was that out of all the levels analyzed the 500 hPa level was the level in which the RH gradient incorporated both tornadoes in both tropical cyclones. While only

248 two tropical cyclones were analyzed this is a pattern/signal that pops up multiple times in the subsequent groupings discussed below.

We also begin to see how the strength of the tropical cyclone may not have as big of a role determining how likely a tornado outbreak will fall under an RH gradient as originally thought. This is seen in the fact that both tropical cyclones and hurricanes are included in groups that produced very little tornadoes under RH gradients. We will also see that tropical cyclones share the same group as strong hurricanes that have the majority of the tornadoes spawned under RH gradients.

Group 3 consisted of tropical cyclones that had 25-49% of each tropical cyclones tornadoes falling under an RH gradient. The tropical cyclones included in this group were

Tropical Storm Allison, Hurricane Frances, Hurricane Ivan, and Hurricane Jeanne. This is the first group to contain major hurricanes in both Ivan and Jeanne. These four tropical cyclones produced a total of 147 tornadoes across 14 different outbreak periods. The majority of the tornadoes in this group were as a result of Hurricane Frances which produced 67 tornadoes and Hurricane Ivan which produced 60 tornadoes due in part to their much larger circulations. The majority of the tornadoes (67%) spawned post landfall. This is opposite of what we saw in the first two groups. This could have easily been caused by the large increase in the number of tornadoes included this group compared to group 1 and 2. The increase friction and vertical shear in the lower levels after landfall also could have contributed to the large increase in post landfall tornadoes.

Out of the 63% of tornadoes that occurred post landfall 40% were located under a RH gradient. This value is only slightly higher than the 36% of pre landfall tornadoes which

249 were located under the RH gradient. Pre landfall vs. post landfall seemed to have very little effect on the amount of tornadoes located under the RH gradient. A strong diurnal cycle was also evident in this group with 66% of the tornadoes occurring during the “day light” hours compared to just 34% occurring after dark. However, there were a larger number of night time tornadoes (44%) that were located under the RH gradient compared to the day time tornadoes (36%). While the large disparity of day time tornadoes vs. night time tornadoes has likely skewed the data we still fail to see any distinguishable patterns or signals that might that might contribute to the likely hood of a tornado outbreak occurring under an RH gradient. This group did produce one interesting result in which the 500 hPa level seemed to be the most common level in which the RH gradient lined up with the tornado outbreak region across the four tropical cyclones discussed in this group.

In fact, out of the 14 separate outbreaks that occurred across the four tropical cyclones a

RH gradient was identified at least partially over a tornado outbreak region during nine of the outbreaks. The next closest level was 400 hPa which was seen to incorporate at least a few tornadoes during five of the 14 separate outbreak periods. We are beginning to see that perhaps dry air in the mid to upper levels of the atmosphere might play the biggest role in helping to demine where a possible tornado outbreak may occur.

It is important to note that up until this point not many patterns/signals have surfaced across the first three groups analyzed. However, the first three groups only make up 36% of the tropical cyclones included in this study. As a result 64% of the tropical cyclones analyzed have more than half of their tornadoes under an RH gradient

250 supporting Curtis claim that there is a relationship between dry air aloft and the location of tornado outbreaks.

The fourth and largest group consisted of tropical cyclones that had 50-74% of their tornadoes under an RH gradient. The tropical cyclones that made up this group were

Tropical Storm Andrea, Hurricane Charley, Hurricane Cindy, Hurricane Dolly, Hurricane

Lili, Hurricane Katrina, and Hurricane Wilma. This group consists of tropical storms of a wide variety of size and strength. These seven tropical cyclones are responsible for 131 total tornadoes with Katrina producing the most with 44 tornadoes. Similarly to what was seen in the previous group the majority of the tornadoes occurred post landfall with 63% of the total tornadoes spawning during that time compared to just 36% occurring pre landfall. However, we still see this play a minor role in dictating the likelihood of the tornado outbreak occurring under the RH gradient since 69% of the pre landfall tornadoes were under the RH gradient and 61% of the post landfall tornadoes were also located under the RH gradient. A strong diurnal cycle is also evident by the fact that 79% of the

131 total tornadoes occurred during the day light hours with only 21% occurring at night.

We also right away notice a big difference between the number of tornadoes under the

RH gradient during the day vs. at night. Out of all the tornadoes that spawned during the day 70% were located under an RH gradient. This value is much higher compared to overnight which only had about 48% of the total overnight tornadoes located under the

RH gradient. To claim that daytime tornado outbreaks are more likely to be under an RH gradient would be premature since this data is heavily skewed towards the day time hours since that is when then three quarters of the tornadoes occurred. What group 4 did show

251 us however that 500 and 400 hPa was were the most common levels that incorporated tornadoes under the RH gradient. Out of the 16 separate outbreaks that occurred there were RH gradients that incorporated tornadoes at 500 and 400 hPa seven and eight times respectively. This is much higher then what we saw at 700 and 300 hPa which had less than three occurrences each. This is the third consecutive group that had 500 hPa identifying the location of the tornado outbreak using RH gradients accurately. We are also seeing 400 hPa emerge as a level that has also accurately pinpointed the location of tornado outbreaks using RH gradient in at least two of the four previous groups.

Group 5 contained tropical cyclones that had 75-99% of their tornadoes occur under an RH gradient. This group consisted of Tropical Storm Alberto, Tropical Storm

Bonnie, Hurricane Gustav, Hurricane Ike, and Tropical Storm Lee producing a total of 99 tornadoes. The wide range in strength of the tropical cyclones included in this group help dispel the notion that only major hurricanes have their associated tornado outbreaks located under RH gradients. About 74% of the tornadoes occurred post landfall and out of all the post landfall tornadoes 90% where located under an RH gradient. This is 17 points higher compared to pre landfall tornadoes where only 73% occurred under the RH gradient. Similar to what is seen in the other groups we see a large diurnal cycle associated with this group. A total of 87% of the tornadoes spawned during the daylight hours leaving 13% which occurred overnight. About 88% of the daylight tornadoes occurred under the RH gradient while only 69% of the overnight tornadoes occurred under the RH gradient. There does seem to be a pattern indicating that daytime tornadoes are more likely to occur under the RH gradient. However, further research is needed to

252 determine if this is as a result of there being more tornadoes in general occurring during the day or if there is some underlying mesoscale or synoptic feature causing this. Group 5 continued the pattern in which most of the tornadoes were located where the RH gradient was positioned at 500 hPa. Out of the 14 individual outbreaks that occurred as a result of the five tropical cyclones included in this group, the RH gradient at 500 hPa lined up with the tornado outbreak region eight times. The next closest levels were 300 and 400 hPa which had RH gradients line up with the tornado outbreak region four out of the 14 total tornado outbreaks.

Group 6 was the final grouping created and consisted of tropical cyclones which were considered “perfect hits” in which all the tornadoes produced were under an RH gradient. Tropical Storm Fay (2002) and Hurricane Rita were the only two tropical cyclones analyzed that fell under this category. A total of 62 tornadoes were produced however, it is important to note that Hurricane Rita was responsible for 53 of the tornadoes while Tropical Storm Fay (2002) only produced 9 tornadoes. As a result the percentages calculated where heavily influenced by Hurricane Rita. 57 tornadoes (92%) occurred post landfall while only 5 tornadoes (8%) occurred pre landfall. Group 6 also demonstrates the diurnal cycle seen in the previous groupings with 66% of the tornadoes occurring during the daylight hours while only 34% occurred at night. Since all the tornadoes in this grouping occurred under the RH gradient one can note make any conclusions whether tornadoes are more likely to occur under an RH gradient post landfall vs. pre landfall or daylight vs. overnight. However, group 6 does seem to be consistent with the previous groups indicating that if an outbreak were to occur under an

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RH gradient it will mostly likely occur post landfall and during the daylight hours.

Finally out of the seven total outbreak periods associated with Tropical Storm Fay (2002) and Hurricane Rita there was no level that had the RH gradient line up with the tornado outbreak region the most. In fact each of the four levels analyzed had two instances in which an RH gradient over a tornado outbreak region could be identified. If it were not for the small sample size I would suspect group 6 to follow the same pattern identified in the previous groups with 500 hPa being the dominate level. All the values calculated for each of the six groups can be seen listed on Table 3.

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Group 1 “Perfect Group 2 Group 3 Miss” “1-24%” “25-49%”

 TS Bill  Hurricane Gabrielle  TS Allison  TS Fay (2008)  Hurricane Irene  Hurricane Frances  Hurricane Ivan  Hurricane Jeanne

Group 4 Group 5 Group 6 “50-74%” “75-99%” “Perfect Hit”

 Hurricane  TS Alberto  TS Fay (2002) Charley  TS Bonnie  Hurricane Rita  Hurricane Wilma  Hurricane Gustav  Hurricane Dolly  Hurricane Ike  TS Andrea  TS Lee  Hurricane Cindy  Hurricane Lili  Hurricane Katrina Table 2. Tropical cyclones associated with each group based on total number of tornadoes located under a RH gradient.

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Group 1 Group 2 Group 3 “Perfect Miss” “1-24%” “25-49%”

 60% pre landfall  0%  52% pre landfall  0%  37% pre landfall  36% under RH gradient under RH gradient under RH gradient  40% post landfall   48% post landfall 18  63% post landfall  0% under RH gradient % under RH gradient 40% under RH gradient

 75% “daylight”  0%  47% “daylight”  9%  66% “daylight”  36% under RH gradient under RH gradient under RH gradient  25% “overnight”  0%  52% “overnight”  8%  34% “overnight”  under RH gradient under RH gradient 44% under RH gradient

 All levels saturated  500 hPa most common  500 hPa most common Group 4 Group 5 Group 6 “50-74%” “75-99%” “Perfect Hit”

 37% pre landfall   26% pre landfall  73%  8% pre landfall  100% 69% under RH gradient under RH gradient under RH gradient  63% post landfall   74% post landfall   92% post landfall  61% under RH gradient 90% under RH gradient 100% under RH gradient

 79% “daylight”  70%  87% “daylight”  88%  66% “daylight”  under RH gradient under RH gradient 100% under RH gradient  21% “overnight”   13% “overnight”   34% “overnight” 48% under RH gradient 69% under RH gradient 100% under RH gradient  400 and 500 hPa most  500 hPa most common common  No one level most common Table 3. Tornado statistics calculated for each grouping.

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Chapter 5: Conclusion and Discussion

A total of 22 tropical cyclones that made landfall along the U.S. and produced at least six tornadoes 24 hours before or after landfall were analyzed in an attempt to recreate the findings presented by Lon Curtis in his paper, “Midlevel Dry Intrusions as a

Factor in Tornado Outbreaks Associated with Landfalling Tropical Cyclones from the

Atlantic and Gulf of Mexico”. Curtis concluded that there was a clear indication the location of tornado outbreaks associated with landfalling tropical cyclones could be pinpointed using steep gradients in RH at various levels. However, the small sample size used prevented any definite statements from being made. In an attempt to discern new patterns and recreate the findings made by Curtis I relaxed the strict criteria used to distinguish qualifying storms which allowed me to almost double the number of tropical cyclones analyzed over a much smaller period of time.

Using the European Centre for Medium-Range Weather Forecasts ERA-Interim reanalysis data alongside with observed soundings from the University of Wyoming each tropical cyclone was separated into one of six groups. The groupings were categorized by the total percentage of tornadoes which occurred under an RH gradient at 300, 400, 500, or 700 hPa. Once each group was finalized various calculations such as percentage of tornadoes that occurred before vs. after landfall or percentage of tornadoes that occurring during the day vs. at night were performed in hopes to distinguish any patterns. Each 257 level for every individual outbreak period was also analyzed to determine which specific level was more likely to have an RH gradient located over the tornado outbreak region.

As a result three distinct observations were noted.

The first observation eliminated the notion that only major hurricanes produce tornadoes that will occur under an RH gradient. While hurricanes were responsible for the majority of the tornadoes such as Frances, Ivan, and Rita a wide variety of tropical cyclones populated each grouping. For example, group 5 which included tropical cyclones that had 75-99% of their tornadoes located under an RH gradient contained major Hurricane Ike and Gustav but also consisted of weak Tropical Storms such as Lee and Bonnie. Group 6 which consisted of tropical cyclones that had all their tornadoes under an RH gradient contained major Hurricane Rita as well as a much weaker Tropical

Storm Fay. On the other side of the spectrum Group 3 which consisted of tropical cyclones that only had 25-49% of the tornadoes under an RH gradient contained major

Hurricane Ivan but also weak Tropical Storm Allison. As a result using steep RH gradients aloft can be applied to any tropical cyclone that threatens to make landfall along the U.S. The challenge of determining which tropical cyclones are most likely to produce a tornado outbreak remains.

The second pattern that was seen within the groupings was an increase in post landfall tornadoes as one increased groups as well as a strong diurnal cycle. For example, group 2 was evenly split between pre landfall tornadoes (57%) and post landfall tornadoes (52%) with a weak diurnal cycle as the majority of the tornadoes (57%) occurred during the overnight hours. This is vastly different then what was seen in the

258 groupings that followed. Group 3 saw a large jump in post landfall tornadoes as 63% of the total tornadoes occurred at this time compared to 37% that occurred pre landfall. We also saw a clear diurnal cycle as 66% of the total tornadoes occurred during the daylight hours vs. 34% that occur at night. The values continue to increase as group 4 also had

63% of the total tornadoes occur post landfall however, the percentage of daytime tornadoes jumped up to 79%. Finally group 5 saw in increase in not only the number of post landfall tornadoes from 63% to 74% but in daytime tornadoes as well up from 79% to 87%. It is important to note that group 2 contains a smaller sample size compared to group 3, 4, and 5. The values for group 2 could be skewed as a result. A more comprehensive analysis over a much longer time frame would help eliminate this issue.

Further research (discussed below) is needed to determine what exactly is leading to this increase in post landfall tornadoes and daytime tornadoes that are located under an RH gradient. However, if a forecaster or researcher wanted to use RH gradients aloft to pinpoint the location of a tornado outbreak then this method seems to work best if the tornado outbreak will occur after the tropical cyclone has made landfall and during the day.

The most noteworthy pattern found in the analysis was that the steep RH gradient pinpointed the tornado outbreaks accurately the most when said RH gradient was located at 500 hPa as seen in table 4. Table 4 indicates that at least 17 of the 22 tropical cyclones analyzed had an RH gradient over at least one tornado outbreak region at 500 hPa. This was followed by 400 hPa which had an RH gradient over at least one tornado outbreak in

16 of the 22 tropical cyclones analyzed. In fact, when each tropical cyclone was broken

259 down into their sub-outbreaks, dry air intrusions at 500 hPa pinpointed the location of tornado outbreaks much more accurately than at 400 hPa. A total of 62 individual tornado outbreaks occurred across the 22 tropical cyclones analyzed. Out of those 62 outbreaks

42 of them had an RH gradient at some level over at least one tornado. RH gradients at

500 hPa were located over the tornado outbreak region a total 27 times. This is much higher than 700 hPa which only matched a total of nine times. This supports one of the findings made by Curtis in which he found that the majority of the qualifying storms he analyzed had low liquid condensation levels indicating a lack of dry air in the first 3 kilometers. Low liquid condensation levels are a condition favorable for tornadogenesis.

400 hPa was the second most common level where RH gradients matched tornado outbreak regions a total of 20 times. 300 hPa had results very similar to what was seen at

700 hPa matching only 10 times. These findings build on the research done by Curtis because Curtis only analyzed the mid to lower atmosphere (500, 700, and 850 hPa). By analyzing the mid to upper atmosphere I was able to determine that both 500 and 400 hPa are the preferred method to use when pinpointing tornado outbreak regions using RH gradients.

One final observation was made when characterizing the location of the RH gradients associated with each tropical cyclone. The RH gradients for each tropical cyclone was separated into one of four categories based on whether the RH gradient was located ahead of the tropical cyclone, behind the tropical cyclone, a dry slot being wrapped around the tropical cyclone and/or other. A table with the characterized location of the RH gradients associated with each tropical cyclone can be seen in table 5. The

260 majority of the tropical cyclones analyzed had a combination of dry air located either ahead or behind the system. These pockets of dry air eventually became dry slots that began to wrap around the anticyclonic rotation of the tropical cyclone. Further analysis over a larger period of time is needed to fully understand where exactly the dry air originated from and what impacts they may have on the location of RH gradients especially ones found over tornado outbreaks. What is also clear is that almost every tropical cyclone analyzed had a RH gradient somewhere in the vicinity. Only three tropical cyclones had outbreaks where no clear evidence of a strong RH gradients was present but instead where characterized with saturated conditions throughout the entire column of the atmosphere.

Based on the four findings discussed above there is much more research needed to be done on this topic. While I was able to double the amount of tropical cyclones analyzed I was still left with a relatively small sample size which skewed some of the data and patterns similar to the results seen in the Curtis paper. Moving forward a comprehensive reanalysis of the tropical cyclones which occurred between 1960 and

2014 using the relaxed criteria used in this paper would undeniable increase the amount of qualifying tropical cyclones allowing for more definitive results.

A complete synoptic and mesoscale reanalysis should also be performed moving forward. Perhaps the tropical cyclones analyzed can be redistributed into new grouping based on the location of the upper level trough/ridge in relation to the tropical cyclone near the time of the tornado outbreaks. Creating a synoptic composite similar to what

Verbout (2007) did showing that landfalling tropical cyclones yield the greatest amounts

261 of tornadoes when there is a 500 hPa trough in the central plains with the tropical cyclone in close proximity to the embedded jet streak might help explain why the 500 hPa level did so well at pinpointing the location of the tornado outbreaks. The large scale synoptic jet pattern may also hint to clues as to where the dry air originated from. A reanalysis of vorticity maximums in relation to the land falling tropical cyclone would also need to be researched to examine the effects of positive/negative vorticity advection and its role during the various tornado outbreaks.

Mesoscale analysis especially near the surface in conjunction with the synoptic composite also cannot be ignored moving forward. A surface analysis may lead to the location of surface boundaries that may play a role in enhancing uplift or tornadogenesis.

Dry air intrusions and its effect on severe weather variables such as CAPE is another area that should not be ignore. By performing a more in depth analysis of the atmosphere around the tropical cyclones may explain the increase in post landfall and daytime tornadoes. A regrouping of the tropical cyclones based on the results of the reanalysis would also be beneficial as each group would contain tropical cyclones with multiple characteristics in common.

Another area for improvement would be to redefine the definition of a tornado outbreak when determining qualifying tropical cyclones. I used the widely accepted definition of an outbreak which required a minimum of six tornadoes proposed by

Galway (1977). As a result a few tropical cyclones included in this paper contained just above the minimum number of tornadoes to qualify but separated into multiple outbreaks that contained 2-3 tornadoes each. These outbreaks also occurred far apart and as long as

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24 hrs apart. This made comparing outbreaks from the same tropical cyclone that did not produce many tornadoes difficult. A more defined way to determine if a tropical cyclone qualified would be if the cyclone produced a tornado outbreak characterized by six or more tornadoes which spawn within a six hour window during the 24 hours before/after landfall. While this would eliminate some of the tropical cyclones included in this paper it would help eliminate anomalous cyclones and allow for more comprehensive comparison of outbreak within the same tropical cyclone due to the larger sample size of tornadoes.

The link between dry air intrusions and tornado outbreaks associated with land falling tropical cyclones could have tremendous impacts on forecasting moving forward.

While it’s true that not all tornado outbreaks have a RH gradient associated with them.

The research proves that there is indeed a connection between the two. Understanding which tropical cyclones are more likely to produce widespread outbreaks will allow us to determine which tropical cyclone will most likely have their associated tornado outbreak located using steep RH gradients aloft. Improvements to models can be made that will allow forecasters to determine the area at risk well in advance. Forecasters should work towards adding this into their arsenal of tools used to forecast tornadoes. This improvement in early detection will undeniably help mitigate disruptions caused by these systems in the future.

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700 hPa 500 hPa 400 hPa 300 hPa Alberto (2006) X X X X Allison (2001) X Andrea (2013) X X Bill (2003) Bonnie (2004) X X Charley (2004) X X Cindy (2005) X X X Dolly (2008) X X Fay (2002) X X X Fay (2008) Frances (2004) X X X X Gabrielle (2001) Gustav (2008) X X X Ike (2008) X X X X Irene (2011) Ivan (2004) X X Jeanne (2004) X X X Katrina (2005) X X X Lee (2011) X X X Lili (2002) X X Rita (2005) X X X X Wilma (2005) X X X Table 4. Examined tropical cyclones with an “X” denoting which level an RH gradient was found over at least one tornado outbreak.

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Ahead of TC Behind TC Dry Slot Other Alberto (2006) X X X Allison (2001) X X Andrea (2013) X Bill (2003) X Bonnie (2004) X X Charley (2004) X X X Cindy (2005) X X Dolly (2008) X X Fay (2002) X X X Fay (2008) X X Frances (2004) X X X Gabrielle X X (2001) Gustav (2008) X X Ike (2008) X Irene (2011) X X Ivan (2004) X X X Jeanne (2004) X Katrina (2005) X X X Lee (2011) X X Lili (2002) X X Rita (2005) X X X Wilma (2005) X Table 5. Characterized location of the RH gradients associated with each tropical cyclone.

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References

Adam K. Baker, Matthew D. Parker, and Matthew D. Eastin, 2009: Environmental Ingredients for Supercells and Tornadoes within Hurricane Ivan. Wea. Forecasting, 24, 223–244 doi: http://dx.doi.org/10.1175/2008WAF2222146.1

Benjamin W. Green, Fuqing Zhang, Paul Markowski Weather and Forecasting Volume 26, Issue 6 (DecehPaer 2011) pp. 828-847. doi: http://dx.doi.org/10.1175/WAF-D-10-05049.1

Cohen AE. 2010. Synoptic-scale analysis of tornado-producing tropical cyclones along the Gulf Coast. Natl. Weather Dig. 34: 99–115.

Curtis, L., 2004: Midlevel dry intrusions as a factor in tornado outbreaks associated with landfalling tropical cyclones from the Atlantic and Gulf of Mexico. Wea. Forecasting, 19, 411–427.

Edwards, R., J. G. LaDue, J. T. Ferree, K. Scharfenberg, C. Maier, and W. L. Coulbourne, 2010: The Enhanced Fujita Scale: Past, present and future. Preprints, 25th Conf. on Severe Local Storms, Denver CO., Amer. Meteor. Soc., 4A.1.

Edwards, R., 2012: Tropical cyclone tornadoes: A review of knowledge in research and prediction. Electronic J. Severe Storms Meteor., 7 (6), 1–61.

Fujita, T. T. , K. Watanabe, K. Tsuchitya, and M. Shimada, 1972: Typhoon-associated tornadoes in Japan and new evidence of suction vortices in a tornado near Tokyo. J. Met. Soc. Japan, 50, 431–453.

Galway, 1977: Some Climatological Aspects of Tornado Outbreaks. Mon. Wea. Rev., 105, 477– 484. doi: http://dx.doi.org/10.1175/1520-0493(1977)105<0477:SCAOTO>2.0.CO;2

266

Gentry, R.C., 1983: Genesis of tornadoes associated with hurricanes. Mon Wea. Rev., 111, 1793– 1805.

Hill, E. L., W. Malkin and W. A. Schulz Jr., 1966: Tornadoes associated with cyclones of tropical origin—practical features. J. Appl. Meteor., 5, 745–763.

Johns, R. H., and C. A. Doswell III, 1992: Severe local storms forecasting. Wea. Forecasting, 7, 588–612.

Johns, R. H., J. M. Davies, and P. W. Leftwich, 1993: Some wind and instability parameters associated with strong and violent tornadoes. Part II: Variations in the combinations of wind and instability parameters. The Tornado: Its Structure, Dynamics, Prediction and Hazards, Geophys. Mongr., No. 79, Amer. Geophys. Union, 583–590.

Lane, Justin D. "ENVIRONMENTAL ASPECTS OF TWO TORNADO OUTBREAKS ASSOCIATED WITH LANDFALLING TROPICAL CYCLONES."

Matthew D. Eastin, Tiffany L. Gardner, M. Christopher Link, Kelly C. Smith Monthly Weather Review Volume 140, Issue 2 (February 2012) pp. 471-491 doi: http://dx.doi.org/10.1175/MWR-D-11-00099.1

McCaul, E. W., Jr., 1987: Observations of Hurricane Danny tornado outbreak of 16 August 1985. Mon. Wea. Rev., 115, 1206–1223.

McCaul, E. W. Jr., 1991: Buoyancy and shear characteristics of hurricane-tornado environments. Mon. Wea. Rev., 119, 1954–1978.

McCaul, E. W. Jr., D. E. Buechler, S. J. Goodman, and M. Cammarta, 2004: Doppler radar and lightning network observations of a severe outbreak of tropical cyclone tornadoes. Mon. Wea. Rev., 132, 1747–1763.

Molinari, J., P. Moore, and V. Idone, 1999: Convective structure of hurricanes as revealed by lightning locations. Mon. Wea. Rev., 127, 520–534.

267

Molinari, J., and D. Vollaro, 2008: Extreme helicity and intense convective towers in Hurricane Bonnie. Mon. Wea. Rev., 136, 4355–4372.

Molinari, J., and D. Vollaro, 2010: Distribution of helicity, CAPE, and shear in tropical cyclones. J. Atmos. Sci., 67, 274–284.

Novlan, D. J., and W. M. Gray, 1974: Hurricane-spawned tornadoes. Mon Wea Rev., 102, 476– 488.

Pearson, A. D., and A. F. Sadowski, 1965: Hurricane-induced tornadoes and their distribution. Mon. Wea. Rev., 93, 461–464.

Powell, M. D., Boundary layer structure and dynamics in outer hurricane rainbands. Part II: Downdraft modification and mixed layer recovery. Mon. Wea. Rev., 118, 918–938.

Powell, M. D., and S. H. Houston, 1996: Hurricane Andrew's landfall in South Florida. Part II: Surface wind fields and potential real-time applications. Wea. Forecasting, 11, 329–349.

Rasmussen, E. N., and D. O. Blanchard, 1998: A baseline climatology of sounding-derived supercell and tornado forecast parameters. Wea. Forecasting, 13, 1148–1164.

Schultz, L. A., and D. J. Cecil, 2009: Tropical cyclone tornadoes, 1950–2007. Mon. Wea. Rev., 137, 3471–3484.

Smith, J. S., 1965: The hurricane-tornado. Mon. Wea. Rev., 93, 453–459. Osamu Suzuki, Hiroshi Niino , Hisao Ohno , Hiroshi Nirasawa , 2010: Tornado-Producing Mini Supercells Associated with Typhoon 9019. Monthly Weather Review, 128, 1868–1882, doi: 10.1175/1520-0493(2000)128<1868:TPMSAW>2.0.CO;2.

Sytske K. KihPaall Monthly Weather Review Volume 134, Issue 7 (July 2006) pp. 1901-1918 doi: http://dx.doi.org/10.1175/MWR3155.1

268

Verbout, S. M., D. M. Schultz, L. M. Leslie, H. E. Brooks, D. J. Karoly and K. L. Elmore, 2007: Tornado outbreaks associated with landfalling hurricanes in the North Atlantic Basin: 1954–2004. Meteor. Atmos. Phys., 97, 255–271.

Vescio, M. D., S. J.Weiss, and F. P. Ostby, 1996: Tornadoes associated with Tropical Storm Beryl. NWA Dig., 1 (21), 2–10.

Wakimoto, R. M., and P. G. Black, 1994: Damage survey of Hurricane Andrew and its relationship to the eyewall. Bull. Amer. Meteor. Soc., 75, 189–200.

Weiss S. J., 1987: Some climatological aspects of forecasting tornadoes associated with tropical cyclones. Preprints, 17th Conf. on Hurricanes and Tropical Meteor., Miami, FL, Amer. Meteor. Soc., 160–163.

269