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

Formation of Hurricanes and Cyclones

Hurricane is a big convection cell

Areas at Risk

Areas at Risk

• Northern hemisphere tropical cyclones:– Rotate counterclockwise, track clockwise

• Southern hemisphere tropical cyclones:– Rotate clockwise, track counterclockwise

Areas at Risk

Areas at Risk

Understanding Motion

• Hurricane track is controlled by Coriolus Effect

Storm Damages

Storm Damages

  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.