Hurricanes

Hurricanes• Intense tropical cyclones with sustained wind

speeds of at least 119 km/h (74 mph)• Warm core systems w/ no associated fronts– Core weakens with altitude (3000 m or 9800 ft)– Becomes anticyclonic aloft

• Characterized by– Eye with diameter 10-60 km (6-40 mi)– Eye wall which is a ring of cumulonimbus clouds– Spiral rain bands reaching no more than 120 km

(75 mi) from the eye

Simplified Hurricane Schematic

Necessary Conditions• Warm sea surface temperatures – greater than

26.5C or 80F• Deep thermocline – greater than 45 m or 150 ft• Significant Coriolis Effect – more than 5 from

equator• Weak vertical wind shear

Locations of Typical Hurricanes

Atlantic Tropical Storms and Hurricanes

Most Atlantic hurricanes occur from August through November

Hurricane Life Cycle• Begin as a tropical disturbance (easterly wave)• Grow to a tropical depression (wind speeds of

37 km/h or 23 mph)• Grow to a tropical storm (wind speeds of 63

km/h or 39 mph)• Grow to a hurricane• Hurricanes weaken– When source of moisture disappears– With influx of cool or dry air

Easterly Waves

• Only 1 in 10 develop into tropical cyclones

• A weak trough of low pressure

• Convergence creates lifting which triggers release of latent heat

Atlantic Hurricane Paths• Paths are often erratic, but

supercomputers can predict them

• From May to June form over Gulf of Mexico and west Caribbean Sea

• July and August form east over the Atlantic

• By mid-September form from east Caribbean Sea to west coast of Africa

• After mid-September back to Gulf of Mexico and west Caribbean Sea

Hurricane Life Cycle

• USGS• NASA video – Overview (1st 8 mins)– Storm track (42:48-45:30)