NATS 101 Lecture 27 Hurricanes

1. NATS 101 Lecture 27Hurricanes

2. Supplemental References for Today’s Lecture Aguado, E. and J. E. Burt, 2001: Understanding Weather & Climate, 2nd Ed.505 pp. Prentice Hall. (ISBN 0-13-027394-5) Danielson, E. W., J. Levin and E. Abrams, 1998: Meteorology. 462 pp. McGraw-Hill. (ISBN 0-697-21711-6)

3. Types of Tropical Cyclones Cyclone TypeWinds Tropical Depression 25-39 mph Tropical Storm 40-74 mph Hurricane/Typhoon  75 mph Most Depressions do not develop into Storms Majority of Storms reach Hurricane status

4. Some Hurricane Extremes Lowest Central PressurePressure Pacific: Typhoon Tip 1979 870 mb Atlantic: Hurricane Wilma 2005 882 mb Costliest HurricanesCost-Loss Hurricane Andrew 1992 $25 billion Hurricane Katrina 2005 $156 billion?* Bangladesh Cyclone 1970 300,000 dead * Burton, Mark L.; Hicks, Michael J. "Hurricane Katrina: Preliminary Estimates of Commercial and Public Sector Damages." Marshall University: Center for Business and Economic Research. September, 2005.

5. Andrew 1992 Time Sequence 2005 Atlantic Hurricanes NASA Note cooler water in wake of Dennis, Emily and Katrina Link to Older NASA Satellite Animations

6. U.S. Hurricane Deaths and Costs Williams, The Weather Book

7. Hurricane Lecture Overview • What are the primary differences between hurricanes and extratropical cyclones? • When and where do hurricanes form? • How do hurricanes intensify? • What is the structure of a hurricane? • What kind damage do hurricanes inflict? • When and where do hurricanes dissipate?

8. Strong Fronts Cold at Storm Center Aloft Strongest Winds Aloft Forms outside Tropics Diameter of 500-1000 miles Energy Source: Horizontal Temperature Contrast No Fronts Warm at Storm Center Aloft Strongest Winds near Surface Forms over Tropical Oceans Diameter of 200-500 miles Energy Source: Energy Fluxes from Warm Ocean Differences Between Tropical and Extratropical Storms Williams, The Weather Book

9. Hot Bed! Tropical Cyclones Hurricanes Typhoons Hurricanes Williams, The Weather Book Where Hurricanes Form? • Hurricanes go by different names in different regions of the world. • Form over warm tropical waters, equatorward of 20 latitude… • Not on equator (poleward of 5 ) b/c non-zero Coriolis is needed. • Occur most frequently over Western North Pacific Ocean.

10. Occur in Warm Season Maximum Likelihood when Sea Surface Temperatures are Warmest-September Average of ~6 Per Year Large Yearly Variability Fewer in El Nino Years More in La Nina Years Atlantic Hurricane Frequency Danielson et al. Fig. 13.2

11. Atlantic hurricanes tend to form in the Middle Tropical Atlantic Ocean and Caribbean Sea They usually propagate westward before turning northward and then northeastward They dissipate rapidly over land Atlantic Hurricane Tracks Danielson et al. Fig. 13.12

12. Hurricane Steering Large-scale flow controls where hurricanes go. Williams, The Weather Book

13. Warm Water with T  82oF Deep Warmth > 200 ft Converging Surface Winds Seedling Low Required Conditionally Unstable Air Supports Deep Convection Widespread, Deep Humid Air Supplies More Latent Heat Weak Vertical Wind Shear Shear Shreds Storm Apart Diverging Winds Aloft Hurricane Necessary Ingredients Williams, The Weather Book

14. Where do Seedling Vortices Come?Lots of Places and Ways Remnant mid-lat circulation Remnant MCC circulation Danielson et al. Fig. 13.14 Vortices along ITCZ Easterly Waves

15. 3D Flow within Hurricanes Winds aloft spiral outward clockwise Winds inside eye spiral downward clockwise Eyewall winds spiral upward c’clockwise Surface winds spiral inward c’clockwise Aguado and Burt, Fig. 12-3

16. Thermal Structure of Hurricane Aguado and Burt, Fig. 12-4

17. Most intense rainfall is along the eyewall. Fastest surface winds are along the eyewall. Region inside of eye is dry with light winds Radar of Andrew’s Landfall Danielson et al. Fig. 13.25 Storm surge cartoon

18. Eye of Hurricane Luis 1995 Luis Visible Eye Animation

19. Asymmetry of Hurricane Winds Region of Maximum Storm Surge 20 kts 100 kts 80 kts 80 kts 60 kts Aguado and Burt, Fig. 12-10

20. Hurricane Intensity Scale (> 980 mb) (965-980 mb) (945-964 mb) (920-944 mb) (< 920 mb) Williams, The Weather Book

21. Primary Hurricane Hazards • Wind Damage Large-Scale Hurricane Circulation Itself Embedded Tornadoes • Flooding Heavy Rains Far Inland, 5”-10” Common Storm Surge along Shoreline

22. Tornadoes embedded within an overland hurricane tend to be weak (category F1-F2) But they are embedded within an environment with 65+ kt winds. Causes hurricane wind damage to be localized. Hurricanes Spawn Tornadoes Aguado and Burt, Fig. 12-11

23. Inland Flooding-Agnes 1972 • Even weak hurricanes can be catastrophic, hundreds of miles inland. • Agnes 1972, category 1 storm for a few hours. • Agnes merged with a slow-moving ET cyclone. • Up to 15” of rain in 24 h fell over Pennsylvania. • Previous flood records exceeded by 6 ft. • Damage > $10B in inflation adjusted dollars. • Costliest U.S. storm prior to Andrew and Katrina.

24. Williams, The Weather Book Storm Surge I • Low atmosphere pressure raises a mound of water inside eye. • Water rises about 1 cm for every 1 mb decrease in pressure. • Inward spiraling winds push more water toward hurricane eye. • Deep hurricanes only raise about 1 meter of water over deep ocean. • Water can sink downward and flow away from the surface.

25. Williams, The Weather Book Storm Surge II • In shallow water near land, water can not flow away under surface. • But winds continue to push water inward towards storm’s center. • Winds along hurricane’s right flank also push water against shore. • Water piles up along shoreline and rushes inland. The big effect! • Effect is worse where ocean floor slopes gently - Gulf of Mexico! • Storm surge cartoon

26. Williams, The Weather Book Storm Surge III • If hurricane hits at high tide, the two effects superimpose. • A 2 ft tide plus a 10 ft surge rises water 12 ft above mean sea level. • Penetration of storm-whipped waves inland worsens damage. • Waves cause far more destruction than the high water alone.

27. Winds and Storm Surge Floyd wave height forecast from RSMAS Danielson et al. Fig. 13.20

28. Surge Damage • Richelieu Apartments before and after landfall of Camille 1969. • Camille was a Category 5 hurricane. • Sustained winds > 180 mph! • Storm surge was 24 feet along the coast! • Many tired citizens took refuge in apartments. • Sadly, several died. http://en.wikipedia.org/

29. Hurricane Decay Andrew Central Pressure Danielson et al. Fig. 13.26 Hurricanes weaken when they make landfall (or go over cool water). Intense surface energy fluxes are cut off and friction increases.

30. Additional Hurricane Information • NASA hurricane images and information • Fall 2005 Atmo 336 section on Hurricanes • 2005 Hurricane season summary • Saharan Air Layer (SAL) and hurricanes (2004) & (2006)

31. Summary: Hurricanes • What are differences between hurricanes and extratropical cyclones? Many significant ones! See earlier slide. • Where and when do hurricanes form? 5-20 latitude over oceans during warm season • How do hurricanes intensify? Energy source is surface energy fluxes from the underlying warm ocean

32. Summary: Hurricanes • What is the structure of a hurricane? Eyewall - strongest winds, heaviest rain Eye - dry with light winds • What kind damage do hurricanes inflict? Can be catastrophic due to high winds, torrential rains, and coastal storm surges • When and where do hurricanes dissipate? At landfall or when they go over cold water