Hurricanes, part 3

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Hurricanes, part 3

• ATS 553

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Storm Surge

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

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Why so destructive?

• 1. Most structures cannot survive being under
  moving water.

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Why so destructive?

• 2. Wind damage is spotty storm surge is
  widespread.

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Why so destructive?

• 3. Takes out expensive civil structures like
  bridges, roads, canals, etc.

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Why so destructive?

• 4. Most expensive development tends to occur
  right along the coast.

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Bangladesh in 1970

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

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What causes storm surge?

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

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What causes storm surge?

• 2. Heavy rains during the hurricane.
• Only a small part of the surge.

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What causes storm surge?

• 3. Strong winds drive the water towards the
  shore.
• Also, EKMAN TRANSPORT!

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Surge is hard to forecast!

• Depends on
• The shape of the coastline
• The shape of the bottom topography
• The lunar tides at landfall

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Climatology of Tropical Storms
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Six basins

• North Atlantic
• Northeast Pacific
• Northwest Pacific
• Northern Indian
• North of Australia
• Northeast of Madagascar

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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

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North Atlantic 9/y

• Why arent there more storms in the N.ATL?
• ITCZ is quite close to the equator
• SSTs arent particularly warm
• TUTT

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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

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Northeast Pacific N. Atlantic

• Number of hurricanes is ANTICORRELATED.
• El Ninowarm water in E. Pacific, good for
  hurricanes.
• But shear is bad for hurricanes in ATL.

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Northwest Pacific 28/y

• Hurricanes all year long.
• More during July-November, when there is a
  monsoon trough in the north Pacific

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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!

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North of Australia 16/y

• NE of Australia---storms move into the SPCZ
• NW of Australia---storms go west into Indian
  Ocean
• Recurve POLEWARD

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Madagascar 10/y

• Storms start in the central Indian ocean.
• Move west and poleward towards Madagascar and
  South Africa

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Monsoon Troughs

• Monsoon troughs are favorable regions for
  tropical cyclone development because

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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

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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!

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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!

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AEWs

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

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Where DONT hurricanes happen?

• Southeast Pacific
• Waters are too cold
• SPCZ is baroclinicwind 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!

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Project STORMFURY

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