CWS 12B - 1 HURRICANE WIND SPEEDS AND PRESSURE CHANGES 1. Print this file and associated images. Also answer the Thursday "Concept of the Day" questions in the Daily Summary File. 2. Complete the Investigation by responding to the Chapter Progress Questions (Study Guide binder) and the introductory portion of Investigation 12B from the Weather Studies Investigations Manual. Congratulations, you are completing the last of 24 Current Weather Studies which have involved Internet-delivered data. We hope you have enjoyed the challenge of DataStreme Atmosphere participation as you have learned the fundamentals of meteorology through the excitement of current environmental data. In addition to being the starting point for weather sensing, analyzing and forecasting in the United States, the National Oceanic and Atmospheric Administration (NOAA) also provides a wealth of weather safety and environmental information via their webpages. For example, http://www.education.noaa.gov/Weather_and_Atmosphere/ has links to weather-related NOAA activities and opportunities of interest for students and others. From the National Hurricane Center's (NHC) main page (http://www.nhc.noaa.gov/), under Hurricane Awareness on the side menu, several items provide potentially life-saving information. "Be Prepared" gives data on historical hurricanes to affect the U.S., hazards of hurricanes and preparedness and action items for an approaching hurricane. Back on the main NHC page, the next menu item under Hurricane Awareness is “Storm Surge”. Here you will find animations of storm surge, often the mostly deadly aspect of hurricanes. Scroll down that page to see results from the Sea, Lake and Overland Surges from Hurricanes (SLOSH) computer model for several notable hurricanes including the historic Galveston 1900 storm, the most deadly natural disaster in U.S. history. Take a few moments to explore the depth and breadth of information available through these pages. 1. The Surge Vulnerability Facts at the bottom of the Storm Surge Overview page tell us that a strong hurricane producing a 23-foot storm surge somewhere along the U.S. Gulf Coast has the ability to flood 57% of arterial roads, almost half of rail miles, 29 airports, and virtually all ports in the area. It would also risk the inundation of [(27%)(49%) (67%)] of interstate highways. Such input is crucial for emergency planners to order evacuations and prepare for possible destruction. [For reference, Hurricane Katrina in 2005 produced a 24 to 28-ft surge over a twenty mile stretch of the Mississippi coast.] Here we take a closer look at the wind fields surrounding the storm centers for major Hurricane Earl and Tropical Storm Hermine, tracks number 5 and 8 respectively on the 2010 hurricane track chart, Image 1 of Current Weather Study 12A. CWS 12B - 2 While pressure patterns surrounding a hurricane center are fairly symmetric, wind patterns in hurricanes are seldom concentric about the eye, particularly when they near land. Image 1 of this Current Weather Studies 12B (courtesy of NOAA Atlantic Oceanographic and Meteorological Laboratory) is the color-coded plot of maximum 1-minute sustained surface wind speeds in knots at 1930Z 30 August 2010 as determined by a U.S. Air Force Hurricane Hunter aircraft when Earl was near its maximum strength north of the British Virgin Islands in the Atlantic Ocean. The eye of Earl is centered in the plot with west longitude along the horizontal axis and north latitude along the vertical. The distance between marks along the vertical and horizontal scales is 0.1 degree or approximately 6 nautical miles (nm). 2. Sea-level pressure as determined from dropwindsondes (essentially rawinsondes dropped from flight level with a parachute) and extrapolations from measurements at flight level (usually 10,000 ft.) is given in the caption immediately above the color-coded graph. At that time the sea-level pressure was determined to be [(925)(955)(975)] mb. Wind speeds are color coded with isotachs at intervals of 5 knots. The highest wind speeds are shaded orange to dark red (darkest in a black and white print) northeast of the center. The unlabeled 65-kt isotach is shown as the heavy black line that makes a distorted oval pattern surrounding the higher wind speeds. Immediately surrounding the much calmer central eye are other heavy isotachs denoting (inward) 65, 50 and 35 kts (the green and blue circular central area). Highlight and label the inner and outer 65-kt isotachs that mark the threshold of hurricane wind speeds. Thin white arrows show the circulation of winds about the eye. The overall storm's movement at that time was toward the west-northwest at 13 kts. 3. The overall flow pattern of winds as shown by the white arrows about the central eye is [(clockwise)(counterclockwise)]. 4. The maximum surface wind speed is given in the caption below the image as [(94)(107)(113)] kts. [The "analyzed" pattern involves many data points including interpolated values from flight level, doppler radar, and satellites while the "observed" winds are from a series of dropwindsondes.] 5. According to the caption, this wind maximum was located 18 nm [(NE)(NW)(SW)(SE)] of the center of the eye. (The eye is positioned where the dashed latitude/longitude lines cross). 6. The surface wind speeds increase from near calm in the center of the eye to hurricane strength (inner heavy 65-kt isotach or green-yellow shading boundary) in about [(2)(5)(9)] nm toward the southwest and nearer elsewhere. (Recall: one division (0.1°) along the latitude and longitude scales equals about 6 n. mi.) This change of wind speed implies an extremely strong horizontal air pressure gradient! 7. As an estimate of the swath of hurricane-force winds to the right side of the track, one can approximate the distance from the heavy inner 65-kt isotach surrounding the eye to the outer 65-kt isotach located at the northeast corner of the graph. The storm's hurricane CWS 12B - 3 force wind speeds of 65 kts and higher on the northeast side extend roughly [(15)(35)(72)] nm. 8. The pattern of hurricane-force winds in this Category 3 hurricane (at flight time; it later strengthened to Category 4) [(forms a symmetric ring about the eye) (is primarily concentrated in the northeast quadrant relative to the eye)]. This pattern illustrates that the internal dynamics of hurricanes and their interactions with the larger- scale flow may produce complex wind patterns. Image 2 (also from NOAA's Atlantic Oceanographic and Meteorological Laboratory) is the plot of maximum surface wind speeds at 0130Z on 7 September 2010 when Tropical Storm Hermine was about to make landfall near Matamoros, Mexico just south of the Texas border (see Image 1 of Monday’s CWS 12A). Again, the eye of Hermine is centered in the plot where the dashed lines cross with longitude along the horizontal and latitude along the vertical axes. The Gulf of Mexico is to the right and the Mexican/U.S. coast is the heavy curve roughly bisecting the image. 9. To the north of the eye, the wind directions as shown by the white arrows, are directed [(onshore)(offshore)]. 10. Given Hermine's forward movement of 17 mph to the north-northwest at this time, the highest winds toward the shore and therefore the highest storm surge would be [(to the left of)(at)(to the right of)] the advancing eye's landfalling position on the storm track. The wind pattern drove water toward Port Lavaca in Texas (north of the map view at 28.6 °N, 96.6 °W) producing a three and a half-foot surge. Mexican area surges are not known. 11. The general effects of rough land versus smoother ocean on the wind speeds can be seen in this wind pattern. For example, observe the wind speeds as depicted by their shadings over the Gulf and over the land. Note and highlight the heavy, unlabeled 35-kt isotach to the upper and lower right over the Gulf. (Recall that isotachs are every 5 knots.) Also highlight where the 35-kt isotach is onshore. This discontinuity in analyzed speeds on opposite sides of the shoreline implies that the wind speed is [(less)(the same)(greater)] on the land side compared to the adjacent ocean side. This change is brought about by the increased frictional drag of the rougher land surface. The National Hurricane Center's report on Earl is at http://www.nhc.noaa.gov/pdf/TCR- AL072010_Earl.pdf. Earl caused $45 million damage, mostly due to flooding and wave damage. Five individuals died in the surf produced by Earl: one in Florida, two in New Jersey, one in Maine and one in Nova Scotia. The National Hurricane Center's report on Hermine is at http://www.nhc.noaa.gov/pdf/TCR-AL102010_Hermine.pdf. Despite the lesser tropical storm (rather than hurricane) strength of Hermine on landfall, it was quite destructive. Other tropical storm hazards resulted in five deaths in Texas and one in Oklahoma (one caught in a rip current, two swimming in a river and three in vehicles washed off roads). There were numerous trees and power lines downed and several tornadoes spawned. Including flooding from copious rainfall, estimated damage was $240 million. CWS 12B - 4 Note this for future reference DataStreme Atmosphere participants: Your successful completion of the DataStreme Atmosphere course with the Wednesday Investigation and Current Weather Study, your final course meeting and submitting the course evaluation, includes 3 graduate semester hours of credit from the State University of New York College at Brockport. The course is officially designated: ESC 675 Real-Time Weather Studies A distance-learning course developing principles of meteorology from analysis of electronically delivered current environmental data and learning activities.