1. Hurricanes

2. Sustained winds at least 74 mph Circulation (c-clkws in N Hem; clkws in S Hem)

3. synonyms Hurricane : north Atlantic, eastern North Pacific Typhoon: western North Pacific Baguio : Philippines Cyclone : India, Australia

4. Typhoon Angela

5. Progression of tropical storms leads to hurricane: 1. tropical disturbances disorganized groups of thunderstorms; some spin: 90% fizzle out 2. tropical depressions : wind speeds 23 mph 3. tropical storm : wind speeds 39 mph (named) 4. hurricane : wind speed 74 mph

6. Begin as “easterly waves” Most Atlantic hurricanes begin in Africa

7. Monsoonal Low Azores Bermuda High Pacific High

8. equator ITCZ Africa ocean SE Trades NE Trades Turned SW by Coriolis deflection

10. At this point, storm is a “tropical disturbance” If storm moves off African continent towards Atlantic, becomes “easterly wave” (carried west by equatorial easterlies) Of approx. 100 each year, 6 become hurricanes

12. Requirements: Warm ocean surface – (>78°F) –Warm to depth of 200 ft –Vast –Basin or current Surface convergence Coriolis deflection –Do not form at equator (5 – 20 °N,S)

13. Hurricane source regions (red arrows) :

17. Anatomy of a hurricane Spiral bands of thunderstorms organized around low pressure center Surface winds converge towards central LOW –Warm, moist air Air aloft diverges around a central HIGH

18. anatomy of a hurricane eyewall –Tallest clouds –Most rain 100 in / day –Highest wind speed Wind speeds strongest here due to conservation of angular momentum eye –air is sinking –Clear skies –Warmer temperatures –15 miles diameter; 1 hour

20. Source of fuel: latent heat of condensation

22. Process of hurricane development: Hurricane starts as tropical storm, clustered thunderstorms spinning around a central low: –Heavy rain –High winds –Release of latent heat (condensation) Increases temperature of cluster Central pressure drops

23. The lower the Low, the higher the winds speeds towards the center Bringing warm flow of warm, moist air More latent heat is released Pressure continues to drop Edge of storm: Outflow sinks and warms

24. Converging moist air and resulting release of latent heat of condensation fuels the process Rises, condenses in eyewall Coriolis deflection makes it spin –Cclkws surface; clkws aloft (N. Hem)

25. Central low pressure Average: 950 mb Typhoon Tip (1979): 870 mb Hurricane Gilbert (1988): 888 mb Hurricane Katrina: 907 mb

26. IR shows height of clouds in eyewall

29. SH_ _ ! We’re in the middle of a ……….. …hurricane???

30. At top of storm: Ice crystals spiral out of storm Create a blanket of cirrostratus cloud cover –Obscures view from above of spiral bands of clouds –On satellite images, hurricanes look like they have uniform thickness and density but they are really strongly banded

32. Andrew

33. Katrina

35. Hurricane Destruction: High Winds (exceed 74 mph) High rainfall (can be as great as several meters per day) Storm surge May contain clusters of short-lived tornadoes flooding

36. Storm surge Sea surface rises and high waves push onshore 2 processes: Piling up of water as heavy winds drag surface water forward to land, causing sea surface to rise Low pressure in storm center causes water to rise –For every 1 mb drop in pressure, water level rises 1 cm Storm surge usually increases sea surface by 3 – 6 feet, but can be extreme

38. Hurricane Camille: storm surge 25 feet 1900 Galveston Hurricane: storm surge 14.5 ft. 8000 drowned (book: Isaac’s Storm) 1970 Bay of Bengal / Bangladesh : storm surge 40 ft. 300,000 – 500,000 fatalities

39. Zones of high storm surge and wind speed: Right-hand side of storm (relative to direction it is moving) in front (“forward right flank”) –Additive effect of wind speed and storm speed

40. Right-forward flank

41. Hurricane Andrew

43. Andrew’s destruction August 1992 –$ 26.5 billion 164 mph peak gust 26 deaths 17’ storm surge 1 tornado 922 mb central pressure Began as tropical wave off west coast Africa, August 14, became Tropical Storm Andrew on Aug 17, became hurricane on Aug. 22, Category 4 Aug 23, blasted Florida Aug. 24

50. Floyd’s destructiveness September 1999 155 mph sustained winds; gusts 185 mph 921 mb One of the largest peacetime evacuations in US 52 deaths rain : 2-3 inches / hour $1 billion

52. Gilbert

54. Saffir-Simpson Scale CATEGORYDAMAGEWINDS STORM SURGE 1minimal74 -95mph4 -5 ft. 2moderate96 -1106 -8 ft. 3extensive111-1309 -12 ft 4extreme131 -15513 -18 ft 5catastrophic> 155> 18 ft

55. Naming hurricanes WWII named by Air Corps and Navy meteorologists after wives and girlfriends Gradually added men’s names North Pacific basin after 2000, given Asian names, not necessarily personal names (flowers, birds, etc)

56. Hurricane watch: landfall > 24 hours Hurricane warning: landfall < 24 hours

57. Arlene Bret Cindy Dennis Emily Franklin Gert Harvey Irene TD #10 José Katrina Lee Maria Nate Ophelia Philippe Rita TD #19 Stan Tammy STD #22 Vince Wilma Alpha Beta Gamma DeltaArlene Bret Cindy Dennis Emily Franklin Gert Harvey Irene TD #10 José Katrina Lee Maria Nate Ophelia Philippe Rita TD #19 Stan Tammy STD #22 Vince Wilma Alpha Beta Gamma Delta