Understanding Hurricane Storm Surge: Causes, Effects, and Historical Impact

1. Hurricanes, part 3 ATS 553

2. Storm Surge • An increase in sea level caused by a landfalling hurricane • Typically 4-8 feet • Typically the most destructive part of the storm.

3. Why so destructive? • 1. Most structures cannot survive being under moving water.

4. Why so destructive? • 2. Wind damage is spotty; storm surge is widespread.

5. Why so destructive? • 3. Takes out expensive civil structures like bridges, roads, canals, etc.

6. Why so destructive? • 4. Most expensive development tends to occur right along the coast.

7. Bangladesh in 1970 • Officially 300,00 people died. • Unofficially, 1 MILLION died • Galveston, 1900 • Worst natural disaster in US history • 7000-8000 people died

8. What causes storm surge? • 1. Low pressure at the center of the storm. • Only responsible for about 1 m of storm surge.

9. What causes storm surge? • 2. Heavy rains during the hurricane. • Only a small part of the surge.

10. What causes storm surge? • 3. Strong winds drive the water towards the shore. • Also, EKMAN TRANSPORT!

11. Surge is hard to forecast! • Depends on: • The shape of the coastline • The shape of the bottom topography • The lunar tides at landfall

12. Climatology of Tropical Storms

13. Six “basins” • North Atlantic • Northeast Pacific • Northwest Pacific • Northern Indian • North of Australia • Northeast of Madagascar

14. North Atlantic • Begin in June or July • Few storms at this time due to TUTT and low SSTs • Peak on September 10 • End in mid November • Formation of STJ, thunderstorm in Amazonia mean more shear

15. North Atlantic – 9/y • Why aren’t there more storms in the N.ATL? • ITCZ is quite close to the equator • SSTs aren’t particularly warm • TUTT

16. Northeast Pacific – 18/y • Sudden onset in June • Trade wind trough becomes a monsoon trough, STJ is gone. • Sudden end in October • Monsoon trough becomes a tradewind trough, STJ redevelops TYPICAL TRACKS:

17. Northeast Pacific & N. Atlantic • Number of hurricanes is ANTICORRELATED. • El Nino—warm water in E. Pacific, good for hurricanes. • But shear is bad for hurricanes in ATL.

18. Northwest Pacific – 28/y • Hurricanes all year long. • More during July-November, when there is a monsoon trough in the north Pacific

19. Northern Indian Ocean • 4/y in Bay of Bengal • 1/y in the Arabian Sea • Why no storms between June and October? • ITCZ is on LAND! • These storms track NORTH!

20. North of Australia – 16/y • NE of Australia---storms move into the SPCZ • NW of Australia---storms go west into Indian Ocean • Recurve POLEWARD

21. Madagascar – 10/y • Storms start in the central Indian ocean. • Move west and poleward towards Madagascar and South Africa

22. Monsoon Troughs • Monsoon troughs are favorable regions for tropical cyclone development because:

23. Monsoon Troughs • 1. They are typically 10° poleward of the equator. • 2. They have cyclonic vorticity. • 3. They have active thunderstorms, pumping lots of humidity into the midlevels of the atmosphere • MORE

24. Monsoon Troughs • 4. High SSTs (because they occur in the late summer and the fall). • 5. High SSTs and radiative cooling of cirrus anvils imply that instability is maintained. • Monsoon troughs have everything a growing TS needs!

25. In the North Atlantic… • Storms are NOT formed by monsoon troughs. • This is the only basin where hurricanes form in flow coming off a large continent. • AEWs!

26. AEWs • About 60% of Atlantic TSs originate from easterly waves. • About 85% of intense hurricanes start that way!

27. Where DON’T hurricanes happen? • Southeast Pacific: • Waters are too cold • SPCZ is baroclinic—wind shear • Rare storms during El Nino • South Atlantic: • SSTs are not all that warm due to upwelling • Far too much shear • ITCZ is always in the northern hemisphere here!

28. Project STORMFURY • Know about Project STORMFURY, its goals and methods, and how this lead to the hurricane hunters.