Hurricanes Weather

Hurricanes  The whirling tropical cyclones that occasionally have wind speeds exceeding 300 kilometers (185 miles) per hour are known in the United States as hurricanes.  In different parts of the world they are called typhoons or just cyclones

Hurricane Formation and Decay  Hurricane Formation  Hurricanes are fueled by latent heat given off when water vapor condenses  Large amounts of warm moist air are needed to drive hurricane formation  Usually during late summer because water temperatures are at least 27°C  This causes few hurricanes to develop poleward of 20°

Hurricane Formation and Decay  Hurricanes generally start formation as a tropical disturbance  This is a disorganized array of clouds and thunderstorms with little rotation.  Not all develop into hurricanes though

Hurricane Formation and Decay  Low pressure develops which creates cyclonic circulation.  If wind speeds and strength increase but do not exceed 61 km/hr it is called a tropical depression  Between 61 and 119 km/hr and now it is officially a tropical storm.

Hurricane Formation and Decay  Tropical Storms can now be named and if they further develop into a hurricane the name remains the same  A Hurricane is officially called when winds reach 119 km/hr

Hurricane Formation and Decay  Generally 80 – 100 tropical storms develop around the world, but only half eventually reach hurricane status.

Hurricane Formation and Decay  Hurricanes decay when:  They move over ocean waters that cannot supply warm, moist tropical air  Move onto land  Reach a location where the largest scale flow aloft is unfavorable.

Hurricane Destruction  Saffir-Simpson Scale  Established to rank the relative intensities of hurricanes  National Weather Service (NWS) assigns a hurricane a category number

Hurricane Destruction  These are based on observed conditions at a particular stage in the life of a hurricane  If conditions change, the category rating can change  5 is the worst, and 1 is the least severe.

Hurricane Destruction  Three classes of hurricane damage:  Storm surge  Wind damage  Inland freshwater flooding

Hurricane Destruction  Storm Surge  The most devastating damage in the coastal area  A storm surge is a dome of water 65 to 80 km wide that sweeps across the coast neat the point where the eye makes landfall  Storm surge is the height of the water above normal tide level  Can exceed 7.5 meters

Hurricane Destruction  Wind Damage  Destruction caused by wind is the most obvious  Hurricanes can produce tornadoes that contribute to the storm’s destructive power.  In 2004 more than 300 tornadoes were generated by hurricanes

Hurricane Destruction  Heavy Rains and Inland Flooding  Heavy sustained raining can cause flooding  Nearly all of the deaths occurred in Haiti as a result of flash floods and mudflows caused by heavy rains

Hurricane Watches and Warnings  A hurricane watch is an announcement aimed at specific coastal areas that a hurricane poses a possible threat, generally within 36 hours  Hurricane warning is issued when sustained winds of 119 km/hr or higher are expected within a specified coastal area in 24 hours or less

Cross section of a hurricane