Tropical Cyclones

Also: Hurricanes,Typhoons

Tropical Cyclone Ingredients

• Light winds instability along I.T.C.Z.• High humidity (oceans) fuel (latent heat)• Warm surface waters over a vast area

(at least 26ºC / 76ºF tropics, < 25 ºN or S)

• Will not form within 5o of equator(no Coriolis)

Tropical Cyclone Features• Spiral bands

• No Fronts

• Eye wall cloud

• Eye• Size: 100-600

miles, but can be larger

Death Toll: 12,000

Tropical Cyclone Formation• Easterly waves (fig. 8-24)

– vertical perturbations within the trade winds– about 10% intensify and rotate

• Tropical depression (winds < 63 kmph, 39 mph)

• Tropical storm (63-118 kmph, 39-73 mph)– naming of the storm

• Cyclone (winds > 119 kmph, 74 mph)– Saffir-Simpson scale (Table 8-1)– ranks 1 to 5 (5 is “catastrophic”)

Saffir-Simpson ScaleCategory Winds Effects

One 74-95 mph

No real damage to building structures. Damage primarly to unanchored mobile homes, shrubbery, and trees. Also, some coastal road flooding and minor pier damage

Two 96-110 mph

Some roofing material, door, and window damage to buildings. Considerable damage to vegetation, mobile homes, and piers. Coastal and low-lying escape routes flood 2-4 hours before arrival of center. Small craft in unprotected anchorages break moorings.

Three 111-130 mph

Some structural damage to small residences and utility buildings with a minor amount of curtainwall failures. Mobile homes are destroyed. Flooding near the coast destroys smaller structures with larger structures damaged by floating debris. Terrain contin

Four 131-155 mph

More extensive curtainwall failures with some complete roof strucutre failure on small residences. Major erosion of beach. Major damage to lower floors of structures near the shore. Terrain continuously lower than 10 feet ASL may be flooded requiring mass

Five greater than 155 mph

Complete roof failure on many residences and industrial buildings. Some complete building failures with small utility buildings blown over or away. Major damage to lower floors of all structures located less than 15 feet ASL and within 500 yards of the sh

Hurricanes, Typhoons & Cyclones

World Map shows locations of Hurricanes, Typhoons & Cyclones

NamesReflectLocations

All are theSame type Of storm

Paths of Hurricanes: North Atlantic

North Atlantic hurricanes develop 5 to 10 degrees north ofThe equator & travel to the west, yet as they move fartherNorth they change directions & move eastward

Most do not makelandfall

Tropical Cyclone Timing(Northern Hemisphere)

Hurricanes:Coastal Damage/DeathCoastal damage can be extensive as high winds, high Tides And ‘storm surges’ push ocean water far inland

Galveston, TexasWas struck in 1900& 6,000 were killed

In 1970 a HurricaneHit Bangladesh &Killed 300,000 in1991 200,000 died

(Note that many people in Australia, Mexico, and S.E. Asia depend on the hurricanes for live-giving moisture each year.)

Tropical Cyclone Hazards

• Storm surge (up to 20 feet)– pressure (1 cm rise per 1 mb drop in pressure)– winds / friction

• rain / floodingcauses mostdamage!

• winds

• tornadoes

Tropical Cyclone Power • Power

– one hour = total USA electricity for one year– one day = nuclear arsenals of USA and Russia

• Highest U.S.death toll: Galveston, TX, 1900 - 20 ft. storm surge killed 6,000 (1/6 the population)

2005 Atlantic Hurricane Season • Most named tropical storms in history (28); including

most intense ever (Wilma: 882 millibars; 185 mph sustained winds) and most Category 5 storms (4) ever

• New Orleans destroyed; worst U.S. hurricane damage ever. Cost estimated at: $100,000,000,000

• Death toll: at least 2048 confirmed dead as of 4/2006; most were among poorest elderly people.

Forecasting and Safety

• Tracking– satellites– coastal radar

• Prediction– computer modeling

• City evacuation plans

Midlatitude cyclone • Forms outside the tropics.• Largest diameter of all storms• No eye• Has distinct fronts.

Extratropical v. tropical cyclones

Tropical cyclone • Forms over a tropical ocean. • Eye and dramatic pressure drop (900 mb or lower) • Has no fronts. • Smaller average size, but much higher winds.

Hurricane & Storm Tracking for the Atlantic & Pacific Oceans - Shows all current hurricanes and their tracks US National Hurricane Center - North Atlantic, Eastern Pacific The Hurricane Hut - Information on all past storms to 1950, along with images and individual storm summaries. Create-a-Cane Interactive fun site from NOAA, allows to specify conditions and see how they impact storm formation NASA Hurricane Web Page - Data, research, science & multimedia resources from NASA WMO guide on cyclone terminology NOVA scienceNOW: Hurricanes

Hurricane Links