Hurricanes, part 3Hurricanes, part 3

ATS 553ATS 553

Storm SurgeStorm Surge

• An increase in sea level caused by a An increase in sea level caused by a landfalling hurricanelandfalling hurricane

• Typically 4-8 feetTypically 4-8 feet

• Typically the most destructive part of Typically the most destructive part of the storm.the storm.

Why so destructive?Why so destructive?

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

Why so destructive?Why so destructive?

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

Why so destructive?Why so destructive?

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

Why so destructive?Why so destructive?

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

Bangladesh in 1970Bangladesh in 1970

• Officially 300,00 people died.Officially 300,00 people died.

• Unofficially, 1 MILLION diedUnofficially, 1 MILLION died

• Galveston, 1900Galveston, 1900– Worst natural disaster in US historyWorst natural disaster in US history– 7000-8000 people died7000-8000 people died

What causes storm surge?What causes storm surge?

• 1. Low pressure at the center of the 1. Low pressure at the center of the storm.storm.

• Only responsible for about 1 m of Only responsible for about 1 m of storm surge.storm surge.

What causes storm surge?What causes storm surge?

• 2. Heavy rains during the hurricane.2. Heavy rains during the hurricane.

• Only a small part of the surge.Only a small part of the surge.

What causes storm surge?What causes storm surge?

• 3. Strong winds drive the water 3. Strong winds drive the water towards the shore.towards the shore.

• Also, EKMAN TRANSPORT!Also, EKMAN TRANSPORT!

Surge is hard to forecast!Surge is hard to forecast!

• Depends on:Depends on:

• The shape of the coastlineThe shape of the coastline

• The shape of the bottom topographyThe shape of the bottom topography

• The lunar tides at landfallThe lunar tides at landfall

Climatology of Tropical Climatology of Tropical StormsStorms

Six “basins”Six “basins”

• North AtlanticNorth Atlantic

• Northeast PacificNortheast Pacific

• Northwest PacificNorthwest Pacific

• Northern IndianNorthern Indian

• North of AustraliaNorth of Australia

• Northeast of MadagascarNortheast of Madagascar

North AtlanticNorth Atlantic

• Begin in June or JulyBegin in June or July– Few storms at this time due to TUTT and Few storms at this time due to TUTT and

low SSTslow SSTs

• Peak on September 10Peak on September 10

• End in mid NovemberEnd in mid November– Formation of STJ, thunderstorm in Formation of STJ, thunderstorm in

Amazonia mean more shearAmazonia mean more shear

North Atlantic – 9/yNorth Atlantic – 9/y

• Why aren’t there more storms in the Why aren’t there more storms in the N.ATL?N.ATL?– ITCZ is quite close to the equatorITCZ is quite close to the equator– SSTs aren’t particularly warmSSTs aren’t particularly warm– TUTTTUTT

Northeast Pacific – 18/yNortheast Pacific – 18/y

• Sudden onset in JuneSudden onset in June– Trade wind trough becomes a monsoon Trade wind trough becomes a monsoon

trough, STJ is gone.trough, STJ is gone.

• Sudden end in OctoberSudden end in October– Monsoon trough becomes a tradewind Monsoon trough becomes a tradewind

trough, STJ redevelopstrough, STJ redevelops

TYPICAL TRACKS:TYPICAL TRACKS:

Northeast Pacific & N. Northeast Pacific & N. AtlanticAtlantic

• Number of hurricanes is Number of hurricanes is ANTICORRELATED.ANTICORRELATED.

• El Nino—warm water in E. Pacific, El Nino—warm water in E. Pacific, good for hurricanes.good for hurricanes.– But shear is bad for hurricanes in ATL.But shear is bad for hurricanes in ATL.

Northwest Pacific – 28/yNorthwest Pacific – 28/y

• Hurricanes all year long.Hurricanes all year long.

• More during July-November, when More during July-November, when there is a monsoon trough in the there is a monsoon trough in the north Pacificnorth Pacific

Northern Indian OceanNorthern Indian Ocean

• 4/y in Bay of Bengal4/y in Bay of Bengal• 1/y in the Arabian Sea1/y in the Arabian Sea

• Why no storms between June and Why no storms between June and October?October?– ITCZ is on LAND!ITCZ is on LAND!

– These storms track NORTH!These storms track NORTH!

North of Australia – 16/yNorth of Australia – 16/y

• NE of Australia---storms move into NE of Australia---storms move into the SPCZthe SPCZ

• NW of Australia---storms go west into NW of Australia---storms go west into Indian OceanIndian Ocean

• Recurve POLEWARDRecurve POLEWARD

Madagascar – 10/yMadagascar – 10/y

• Storms start in the central Indian Storms start in the central Indian ocean.ocean.

• Move west and poleward towards Move west and poleward towards Madagascar and South AfricaMadagascar and South Africa

Monsoon TroughsMonsoon Troughs

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

Monsoon TroughsMonsoon Troughs

• 1. They are typically 10° poleward of 1. They are typically 10° poleward of the equator.the equator.

• 2. They have cyclonic vorticity.2. They have cyclonic vorticity.

• 3. They have active thunderstorms, 3. They have active thunderstorms, pumping lots of humidity into the pumping lots of humidity into the midlevels of the atmospheremidlevels of the atmosphere

• MOREMORE

Monsoon TroughsMonsoon Troughs

• 4. High SSTs (because they occur in 4. High SSTs (because they occur in the late summer and the fall).the late summer and the fall).

• 5. High SSTs and radiative cooling of 5. High SSTs and radiative cooling of cirrus anvils imply that instability is cirrus anvils imply that instability is maintained.maintained.

• Monsoon troughs have everything a Monsoon troughs have everything a growing TS needs!growing TS needs!

In the North Atlantic…In the North Atlantic…

• Storms are NOT formed by monsoon Storms are NOT formed by monsoon troughs.troughs.

• This is the only basin where hurricanes This is the only basin where hurricanes form in flow coming off a large form in flow coming off a large continent.continent.

• AEWs!AEWs!

AEWsAEWs

• About 60% of Atlantic TSs originate About 60% of Atlantic TSs originate from easterly waves.from easterly waves.

• About 85% of intense hurricanes About 85% of intense hurricanes start that way!start that way!

Where DON’T hurricanes Where DON’T hurricanes happen?happen?

• Southeast Pacific:Southeast Pacific:– Waters are too coldWaters are too cold– SPCZ is baroclinic—wind shearSPCZ is baroclinic—wind shear– Rare storms during El NinoRare storms during El Nino

• South Atlantic:South Atlantic:– SSTs are not all that warm due to upwellingSSTs are not all that warm due to upwelling– Far too much shearFar too much shear– ITCZ is always in the northern hemisphere ITCZ is always in the northern hemisphere

here!here!

Project STORMFURYProject STORMFURY

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