Hurricanes

Sustained winds at least 74 mph

Circulation (c-clkws in N Hem; clkws in S Hem)

synonymsHurricane : north Atlantic, eastern North Pacific

Typhoon: western North Pacific

Baguio : Philippines

Cyclone : India, Australia

Typhoon Angela

Progression of tropical storms leads to hurricane:1. tropical disturbancesdisorganized groups of thunderstorms; some spin: 90% fizzle out2. tropical depressions : wind speeds 23 mph3. tropical storm : wind speeds 39 mph (named)4. hurricane : wind speed 74 mph

Begin as easterly waves Most Atlantic hurricanes begin in Africa

Monsoonal LowAzores Bermuda HighPacific High

equatorITCZAfricaoceanSE TradesNE TradesTurned SW by Coriolis deflection

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

Requirements:Warm ocean surface (>78F)Warm to depth of 200 ftVastBasin or currentSurface convergenceCoriolis deflectionDo not form at equator (5 20 N,S)

Hurricane source regions (red arrows) :

Anatomy of a hurricaneSpiral bands of thunderstorms organized around low pressure center

Surface winds converge towards central LOWWarm, moist air

Air aloft diverges around a central HIGH

anatomy of a hurricaneeyewall Tallest clouds Most rain100 in / dayHighest wind speedWind speeds strongest here due to conservation of angular momentum

eyeair is sinkingClear skiesWarmer temperatures15 miles diameter; 1 hour

Source of fuel: latent heat of condensation

Process of hurricane development:Hurricane starts as tropical storm, clustered thunderstorms spinning around a central low:Heavy rainHigh windsRelease of latent heat (condensation) Increases temperature of clusterCentral pressure drops

The lower the Low, the higher the winds speeds towards the centerBringing warm flow of warm, moist airMore latent heat is releasedPressure continues to dropEdge of storm:Outflow sinks and warms

Converging moist air and resulting release of latent heat of condensation fuels the process

Rises, condenses in eyewall

Coriolis deflection makes it spinCclkws surface; clkws aloft (N. Hem)

Central low pressure

Average: 950 mb

Typhoon Tip (1979): 870 mb

Hurricane Gilbert (1988): 888 mb

Hurricane Katrina: 907 mb

IR shows height of clouds in eyewall

SH_ _ ! Were in the middle of a ..hurricane???

At top of storm:Ice crystals spiral out of storm

Create a blanket of cirrostratus cloud coverObscures view from above of spiral bands of cloudsOn satellite images, hurricanes look like they have uniform thickness and density but they are really strongly banded

Andrew

Katrina

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 tornadoesflooding

Storm surgeSea surface rises and high waves push onshore2 processes:Piling up of water as heavy winds drag surface water forward to land, causing sea surface to riseLow pressure in storm center causes water to riseFor every 1 mb drop in pressure, water level rises 1 cmStorm surge usually increases sea surface by 3 6 feet, but can be extreme

Hurricane Camille: storm surge 25 feet

1900 Galveston Hurricane: storm surge 14.5 ft.8000 drowned (book: Isaacs Storm)

1970 Bay of Bengal / Bangladesh : storm surge 40 ft. 300,000 500,000 fatalities

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

Right-forward flank

Hurricane Andrew

Andrews destructionAugust 1992

$ 26.5 billion 164 mph peak gust26 deaths17 storm surge1 tornado922 mb central pressureBegan 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

Floyds destructivenessSeptember 1999

155 mph sustained winds; gusts 185 mph921 mbOne of the largest peacetime evacuations in US52 deathsrain : 2-3 inches / hour$1 billion

Gilbert

Gilbert

Saffir-Simpson ScaleCATEGORYDAMAGEWINDS STORM SURGE

1minimal74 -95mph4 -5 ft.2moderate96 -1106 -8 ft.3extensive111-1309 -12 ft4extreme131 -15513 -18 ft5catastrophic> 155> 18 ft

Naming hurricanesWWII named by Air Corps and Navy meteorologists after wives and girlfriends

Gradually added mens names

North Pacific basin after 2000, given Asian names, not necessarily personal names (flowers, birds, etc)

Hurricane watch: landfall > 24 hours

Hurricane warning: landfall < 24 hours

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