2) Tropical Cyclones2) Tropical Cyclones

Tropical CyclonesTropical Cyclones

Occur in tropical and subtropical zonesOccur in tropical and subtropical zones

They range in intensity from a mild disturbance to highly They range in intensity from a mild disturbance to highly destructive hurricanes or typhoonsdestructive hurricanes or typhoons

Multiple bands of inspiriling thunderstorms fuel the storm Multiple bands of inspiriling thunderstorms fuel the storm with large amounts of latent heatwith large amounts of latent heat

They move westward in the tropics due to the NE/SE trade They move westward in the tropics due to the NE/SE trade windswinds

Weather of the TropicsWeather of the Tropics

Dominated by a single air mass Dominated by a single air mass –– mEmE

No frontal activity No frontal activity –– midlatitudes onlymidlatitudes only

Easterly flow of air converging at the ITCZEasterly flow of air converging at the ITCZ

Isobars should be parallel with lines of latitudeIsobars should be parallel with lines of latitude

Disturbances in isobars forms an equatorial trough, called Disturbances in isobars forms an equatorial trough, called an an Easterly WaveEasterly Wave

Circulation around the easterly wave is cyclonicCirculation around the easterly wave is cyclonic

When coupled with surface heating and convection, the When coupled with surface heating and convection, the rising air and cyclonic rotation can be increasedrising air and cyclonic rotation can be increased

If this circulation becomes more well defined, we have a If this circulation becomes more well defined, we have a Tropical DepressionTropical Depression

Tropical depressions are frequently seen from August to Tropical depressions are frequently seen from August to October (NH)October (NH)

Fueled by warm tropical waters which enhance convection Fueled by warm tropical waters which enhance convection and moisture contentand moisture content

If the tropical depression develops further with maximum If the tropical depression develops further with maximum sustained winds at 35 mph (56 kph) and closed isobaric sustained winds at 35 mph (56 kph) and closed isobaric flow, then we have a flow, then we have a Tropical StormTropical Storm

Further development of the tropical storm may result from Further development of the tropical storm may result from continued movement over warm, tropical waters or from a continued movement over warm, tropical waters or from a simple poleward movement (enhanced coriolis)simple poleward movement (enhanced coriolis)

If maximum sustained winds reach 74 mph (118 kph) we If maximum sustained winds reach 74 mph (118 kph) we have a Tropical Cyclonehave a Tropical Cyclone

Also called a Also called a hurricane hurricane (N. America), (N. America), a typhoona typhoon (eastern (eastern Pacific), a Pacific), a CycloneCyclone (Indian Ocean), or a (Indian Ocean), or a WillyWilly WillyWilly (Australia)(Australia)

Easterly waves have surface convergence and cloud coverEasterly waves have surface convergence and cloud covereast of the axis and divergence to the west.east of the axis and divergence to the west.

A cross section of a typical hurricane.A cross section of a typical hurricane.

Hurricane Floyd Hurricane Floyd –– 19991999

Weather of the TropicsWeather of the Tropics

Characteristics of a hurricane include:Characteristics of a hurricane include:Inward flow of rising airInward flow of rising airInward spiral of air characterized by cloud bandsInward spiral of air characterized by cloud bandsAn area of strong lowAn area of strong low--pressurepressureA wellA well--defined eyedefined eye--wall with weak wall with weak descendingdescending air in the air in the centercenter

Hurricanes will move from east to west in the tropics Hurricanes will move from east to west in the tropics and curve toward the east as they move into midand curve toward the east as they move into mid--latitudeslatitudes

Weather of the TropicsWeather of the Tropics

As long as there are warm waters beneath them, As long as there are warm waters beneath them, hurricanes will continue to develophurricanes will continue to developAs they move inland, they dissipate rather quickly As they move inland, they dissipate rather quickly due todue to

Friction with the land surfaceFriction with the land surfaceA loss of the warm supply of moistureA loss of the warm supply of moisture

SaffirSaffir--Simpson Hurricane ScaleSimpson Hurricane Scale

CategoryCategory WindsWinds DamageDamage11 74 74 -- 95 mph95 mph MinimalMinimal22 96 96 -- 110 mph110 mph ModerateModerate33 111111--130 mph130 mph ExtensiveExtensive44 131131--155 mph155 mph ExtremeExtreme55 > 155 mph> 155 mph CatastrophicCatastrophic

(Category 5 (Category 5 –– Labor Day Hurricane, 1935 Labor Day Hurricane, 1935 –– FL KeysFL KeysHurricane Camille, 1969 Hurricane Camille, 1969 –– LA, MS)LA, MS)

HurricanesHurricanes

Widespread FloodingWidespread Floodingeven weak storms can produce heavy rainseven weak storms can produce heavy rains

High WindsHigh Windswinds can exceed 100 mphwinds can exceed 100 mph

Storm SurgeStorm Surgecoastal areas affected by water pushed ashorecoastal areas affected by water pushed ashore

TornadoesTornadoesnot as severe as tornadoes in the Midwestnot as severe as tornadoes in the Midwest

HurricanesHurricanes

Over the last 30 years, more than half of the Over the last 30 years, more than half of the hurricanehurricane--related deaths have occurred due to inland related deaths have occurred due to inland floodingflooding

Storm surges are a potential threat, but most people Storm surges are a potential threat, but most people evacuateevacuate

Rainfall totals are Rainfall totals are notnot proportional to the wind speed proportional to the wind speed –– most heavy flooding occurs with minor storms that most heavy flooding occurs with minor storms that stall over an area.stall over an area.

HurricanesHurricanes

Storm Surge Storm Surge –– 6000 people killed by the Galveston 6000 people killed by the Galveston Hurricane of 1900Hurricane of 1900

Storm Surge Storm Surge –– Hurricane Camille (1969) produced a Hurricane Camille (1969) produced a 25 foot storm surge25 foot storm surge

Storm Surge Storm Surge –– Hurricane Hugo (1989) produced a 20 Hurricane Hugo (1989) produced a 20 foot storm surgefoot storm surge

Heavy Winds Heavy Winds –– Hurricane Hugo (1989) produced 100 Hurricane Hugo (1989) produced 100 mph winds in Charlotte, NCmph winds in Charlotte, NC

The storm surge is a combination of theThe storm surge is a combination of thewindwind--driven surge and the pressure surge.driven surge and the pressure surge.The windThe wind--driven effect is by far the mostdriven effect is by far the most

significant.significant.

Wind speed variations by quadrantWind speed variations by quadrant

Average tornado locations relativeAverage tornado locations relativeto hurricane storm centerto hurricane storm center

HurricaneHurricaneGordonGordon

Nov. 8Nov. 8--212119941994

GulfstreamGulfstream IV/SPIV/SP

Lockheed WPLockheed WP--3D Orion3D Orion