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Tropical Cyclones Chapter 11 Meteorology 1010 Professor Bunds Utah Valley University typhoons hurricanes cyclones Tropical Cyclone Naming, Paths and Seasons Paths of All Tropical Cyclones 1985 - 2005 Hurricane Air Flow Upper Level Hurricane Air Flow Hurricane Rankings SaffirSimpson Category Maximum sustained wind speed Minimu m surface pressure Storm surge mph m/s kts mb ft m 1 74-95 33-42 64-82 greater than 980 3-5 1.0-1.7 2 96-110 43-49 83-95 979-965 6-8 1.8-2.6 3 111-130 50-58 96-113 964-945 9-12 2.7-3.8 4 131-155 59-69 114-135 944-920 13-18 3.9-5.6 5 156+ 70+ 136+ less than 920 19+ 5.7+ Hurricane Formation • Powered largely by warm water • Hurricanes are most common late summer to fall – ‘hurricane season’ – Varies by region • Weaken over land – Usually weaken as they approach coastline also • Form near but not over equator, given proper conditions (next slide) Ingredients for Hurricane Formation • • • • • • • Warm water – at least 80oF Relatively cool air at altitude Relatively moist air at moderate altitude (3 miles up) At least 300 miles from the equator Little wind shear between surface and upper air (6 miles up) Divergence aloft A trigger – e.g., big thunderstorms Hurricane Hazards • Storm Surge – On average, the biggest threat to life and property • Winds • Flooding from extreme precipitation – Can cause major problems far inland Galveston Hurricane, 1900 > 10,000 fatalities, worst natural disaster in U.S. history Storm Surge Tropical Cyclone Winds & Storm Surge Hurricane Ike Storm Surge September 2008 Hurricane Ivan 10 am Friday Link to visible loop Hurricane Ivan Link to visible loop 10 am Friday Hurricane Ivan 1:45pm Thursday Hurricane Ivan 1:45pm Thursday link to infrared loop Hurricane Ivan 9:45pm Friday link to infrared loop Hurricane Ivan 9:45pm Friday link to infrared loop Link to visible loop Link to IR loop Ivan, 9.15.04 11:15 am EDT Ivan, 9.15.04 10:45 am EDT Mississippi Delta Mississippi ‘wants’ to follow course of Atchafalaya River Active Lobe ~ 500 years old Mississippi River Delta Ivan, 9.17.04 4:15 pm EDT Hurricane Ike Storm Surge September 2008 Path of hurrican and locations of tidal gauges that recorded storm surge, as shown on following slides This and following photos are of Galveston, TX, and nearby areas Houston, TX High Island, Texas Gilchrist, Texas Orange, Texas