Hurricanes
Hurricanes are fueled by warm ocean waters, forming in the tropical latitudes when water temperatures exceed 80° F. The process of hurricane generation begins when water evaporates at the sea surface, and the resulting warm, moist air rises into the atmosphere. As the air rises, the moisture condenses to form clouds and thunderstorms. The energy released from the condensation, a process called the latent heat of condensation, warms the cool atmosphere above causing more air to rise. Additional warm, moist air rises from the ocean surface to replace the air above, causing the pressure at the surface to continue to fall. Resulting winds blow in towards the low-pressure center and, in the Northern Hemisphere, circulate in a counter-clockwise fashion forming the familiar cyclonic wind pattern of a hurricane.
A storm system is formally defined as a hurricane when wind speeds reach 74 mph. The five categories of hurricane intensity are defined by the Saffir-Simpson Scale. According to this scale, the most intense hurricane is a Category 5, with wind speeds exceeding 155 mph. Only two Category 5 hurricanes have made landfall in the United States in recorded history. For perspective, Hurricane Katrina made landfall in August 2005 as a Category 3 storm with wind speeds of 125 mph.
Because hurricane winds travel in a counter-clockwise direction, surface winds to the right of the hurricane's eye pile water up against the coastline, creating a coastal storm surge. This area to the right of the eye is known as the right-front quadrant, and is the most dangerous part of the storm during landfall. The amount of damage done by a hurricane is dependent on several factors, including wind speed, elevation of storm surge, the forward speed of the hurricane, and the radius of hurricane force winds.
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U.S. Department of the Interior |
U.S. Geological Survey
