Late Season Tropical Cyclogenesis in the Northeastern Atlantic Ocean: 1975-2005 Rachel Grant Mauk Department of Geography, The Ohio State University, Columbus OH 43210

An Atypical Area Basic Types of Conclusions • Late season tropical cyclones • LSTCs develop from four unique (LSTCs) not uncommon origins TROPICAL SUBTROPICAL •Twenty LSTCs formed in NE Atlantic • Spatial correlation with type • Organized clouds at • Limited clouds at from Oct-Dec in 1975-2005 seasons center center • Type II near (30N,50W) • Ten formed from 2000-2005 • Non-frontal • Non-frontal •Type III in high latitudes •Nine tropical , eleven • Warm at upper-level • Cold at upper-level •Type IV in SW sector hurricanes, no major hurricanes center center • Average SST is 24.7C • High wind shear, low sea surface • Maximum winds • Maximum winds away temperatures (SSTs) common close to center from center • Tropical development threshold • Scale < 500 km • Scale < 750 km 26.5C (Bosart and Bartlo 1991) •Environment usually unfavorable for tropical development • Wind shear highly variable within Figure 3. Position of each LSTC at time of genesis. Thick black lines types EXTRATROPICAL demarcate spatial boundaries for the study. Type I Type II Type III Type IV • Area of lower shear co-located • Variable cloud with Type I, II, III genesis location Why Study LSTCS? •Maximum winds patterns 5 105 Figure 1. Diagram of three away from center • Tropical cyclogenesis in any • Frontal or non-frontal 95 basic cyclone types. • Scale < 2000 km 4 environment not completely Tropical image is of • Cold at upper-level 85 center Future Work understood Hurricane Katrina (2005). 3 75 Subtropical imagery is of 65 • Project will be continued as Master’s • Transition from extratropical or Subtropical Andrea 2 55 thesis subtropical to not (2007). Extratropical CountLSTC system is from May 2003. 45 understood Satellite imagery courtesy 1 MaximumIntensity (kts) • Continue analysis of local 35 • “Hybrid” systems (between Earth Observatory, NASA environment GSFC. 0 25 subtropical and tropical) also not 1975 1980 1985 1990 1995 2000 2005 25 35 45 55 65 75 • Vertical temperature gradients understood Year Initial Intensity (kts) • Horizontal vorticity (tendency to •Affect shipping, occasionally land Figure 4. Histogram of LSTCs by year. Figure 5. Graph of maximum intensity versus intensity at genesis. rotate) anomalies • US, Canada, Bermuda, • Move from genesis to persistence Caribbean, Azores, Europe • How do LSTCs survive in low 850-200hPa Shear and SST Classification of LSTCs a) SST/high shear environments? • Destructive: 1991 “Perfect Storm”, 16.0 a) Noel 2007 14.0 12.0 • Ten LSTCs since 2000: influence of TYPE I (6) TYPE II (7) 10.0 References climate change? Initial system is Shear Initial system is a 8.0 non-tropical, (m/s) Bosart, L. F., and J. Bartlo, 1991: Tropical frontal low. Front 6.0 non-frontal, and cyclone formation in a baroclinic environment. stalls in central 4.0 pre-existing. Mon. Wea. Rev., 119, 1979-2013. Atlantic, low spins 2.0 Project Details Convection fires up as frontal 0.0 Kalnay et al.,1996. The NCEP/NCAR 40-year Systems selected for: near center of structure 21.00 22.00 23.00 24.00 25.00 26.00 27.00 28.00 29.00 reanalysis project. Bull. Amer. Meteor. Soc., system, wind SST (C) dissipates. 77, 437-470. • Location: north of 20ºN, east of 60ºW radii contract. 850-300hPa Shear and SST Reynolds, R.W., et al., 2002: An Improved In • Time: after 1 Oct. from 1975-2005 b) 14.0 b) Situ and Satellite SST Analysis for Climate. J. TYPE III (3) TYPE IV (4) Climate, 15, 1609-1625. •Consistent satellite classification 12.0 Initial system is Initial system is after 1975 10.0 an occluded tropical wave • National Hurricane Center (NHC) extratropical or circulation. Shear 8.0 designation: cyclone. Frontal Development (m/s) 6.0 Acknowledgments •Tropical AND structure occurs by 4.0 This project was funded by an Undergraduate dissipates, typical tropical Research Scholarship from the Colleges of •Maximum wind ≥34 knots FOR 2.0 convection fires process. 0.0 the Arts and Sciences. Their generosity is •≥6 hours around low. 21.00 22.00 23.00 24.00 25.00 26.00 27.00 28.00 29.00 greatly appreciated. • Wind data from NCEP/NCAR SST (C) I would like to thank the Honors College for all Reanalysis II (Kalnay et al. 1996) Figure 2. Visible satellite images and genesis descriptions of one system from each LSTC type. Figure 6. Graphs of shear and SST averaged over 24 hours Figure 7. Shear contour plots for the opportunities they have provided during Number in parentheses is number of systems matching each type. Images are taken from the Naval prior to genesis for a) 850-200hPa and b) 850-300hPa layers. Florence 1994 (Type II). Note the my time here. I also thank my Honors adviser, -1 •SST data from Reynolds Weekly SST Research Labs’ Tropical Cyclone Page, Marine Meteorology Division, Monterey, California. Shear and SST calculated on 5x5 grids centered on system. increase in coverage of 5 m s Joanna Spanos, and my thesis adviser, Dr. contour from 200hPa to 300hPa. fields v. 2 (Reynolds et al. 2002) Type I Type II Type III Type IV Jay Hobgood, for supporting me in academics and in life. I would not be what I am without your guidance.