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Natural Hazards and Disasters Chapter 14 Hurricanes and Nor’easters. Terminology. Hurricanes : N. Atlantic and E. Pacific Typhoons : W. Pacific, Japan, SE Asia Cyclones : Indian Ocean All are low pressure systems in the tropics Lower winds are tropical depressions or storms.
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Natural Hazards and Disasters Chapter 14 Hurricanes and Nor’easters
Terminology • Hurricanes: N. Atlantic and E. Pacific • Typhoons: W. Pacific, Japan, SE Asia • Cyclones: Indian Ocean • All are low pressure systems in the tropics • Lower winds are tropical depressions or storms
Formation of Hurricanes • Rising air and condensation creates convective ‘chimney’ of thunderstorms • Strong winds inhibit convection • Warm seawater promotes hurricanes • Winds exceed 119 km/hr
Formation of Hurricanes and Cyclones • Warm air expands, cools and releases latent heat • Eye is 20oC warmer than surrounding air • Rising air pulls more air into center of hurricane • 160-800 km in diameter • Forward motion averages 25 km/hr • Winds drop abruptly in eye, pressure drops
Areas at Risk • Northern hemisphere tropical cyclones: • Rotate counterclockwise, track clockwise • Southern hemisphere tropical cyclones: • Rotate clockwise, track counterclockwise
Understanding Motion • Hurricane track is controlled by Coriolus Effect
CAT 1 CAT 2 CAT 3 CAT 4 CAT 5 WIND SPEED 74-95 MPH 96-110 MPH 111-130 MPH 131-155 MPH >156 MPH STORM SURGE 4-5 FT 6-8 FT 9-12 FT 13-18 FT >19 FT PRESSSURE 980 MBARS 965-979 MBARS 945-964 MBARS 920-944 MBARS <920 MBARS SAFFIR-SIMPSON SCALE
Hurricane Related Hazards • Storm surge • Wave damage • Wind damage • Rainfall and flooding • Disease and starvation
HURRICANE-PRODUCED CONDITIONS • Storm surge - Tropical cyclones cause an increase in sea level, which can flood coastal communities. This is the worst effect, as hurricanes claim 80% of their victims when they first strike shore.