Transcript for Anatomy of a Hurricane, segment 03 of 5


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The central area of lowest pressure is called the eye of the hurricane, a calm, often cloud-free area from four to forty miles across. Immediately surrounding the eye is the eye wall, a cylindrical band of highest winds and the location of the storm's most concentrated violence. Air at the sea surface is sucked towards the eye and thrust upwards in the eye wall after forming rain bands on its trip inwards. As it rises, moist air cools, causing water to condense as a fine mist or ice while releasing huge amounts of heat. An average hurricane releases heat equivalent to the total electrical energy consumed annually in the United States. This liberated heat causes air to rise even further, producing more condensation and releasing still more heat. In this manner a hurricane drives itself, pulling in moisture-laden warm air at its base, extracting heat and water, and then propelling the air outward near elevations of fifty thousand feet.

Huge amounts of rainfall are often a by-product of this energy transfer with as much as twenty inches of rain measured beneath a passing storm. Flash floods associated with this rainfall can cause extensive erosion, carrying large volumes of sediment seaward. Hurricanes are pushed by the tradewinds at up to twenty miles per hour, generally traveling from their low latitude origins toward the poles. Once over cold water or land, a hurricane's warm water energy supply is cut, causing it to weaken and die.