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- Hurricanes
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- Hurricanes get their start over the warm tropical waters of the North
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- Atlantic Ocean near the equator. Most hurricanes appear in late summer or
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- early fall, when sea temperatures are at their highest. The warm waters
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- heats the air above it, and the updrafts of warm, moist air begin to rise.
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- Day after day the fluffy cumuli form atop the updrafts. But the cloud
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- tops rarely rise higher than about 6,000 feet.
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- At that height in the tropics, there is usually a layer of warm, dry air
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- that acts like an invisible ceiling or lid.
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- Once in a while, something happens in the upper air that destroys
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- this lid. Scientist don not know how this happens. But when it does, it's
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- the first step in the birth of a hurricane.
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- With the lid off, the warm, moist air rises higher and higher. Heat
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- energy, released as the water vapor in the air condenses. As it condenses
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- it drives the upper drafts to heights of 50,000 to 60,000 feet. The
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- cumuli become towering thunderheads.
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- From outside the storm area, air moves in over the sea surface to
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- replace the air soaring upwards in the thunderheads. The air begins
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- swirling around the storm center, for the same reason that the air
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- swirls around a tornado center.
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- As this air swirls in over the sea surface, it soaks up more and
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- more water vapour. At the storm center, this new supply of water vapor
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- gets pulled into the thunderhead updrafts, releasing still more energy
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- as the water vapor condenses. This makes the updrafts rise faster,
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- pulling in even larger amounts of air and water vapor from the storm's
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- edges. And as the updrafts speed up, air swirls faster and faster around
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- the storm center. The storm clouds, moving with the swirling air, form a
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- coil.
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- In a few days the hurricane will have grown greatly in size and
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- power. The swirling shape of the winds of the hurricane is shaped like a
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- dough-nut. At the center of this giant "dough-nut" is a cloudless, hole
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- usually having a radius of 10 miles. Through it, the blue waters of the
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- ocean can be seen. The hurricane's wind speed near the center of the
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- hurricane ranges from 75 miles to 150 miles per hour.
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- The winds of a forming hurricane tend to pull away from the center
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- as the wind speed increases. When the winds move fast enough, the "hole"
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- developes.
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- This hole is the mark of a full-fledge hurricane. The hole in the
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- center of the hurricane is called the "eye" of the hurricane. Within the
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- eye, all is calm and peaceful. But in the cloud wall surrounding the eye,
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- things are very different.
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- Although hurricane winds do not blow as fast as tornado winds, a
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- hurricane is far more destructive. That's because tornado winds cover
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- only a small area, usually less than a mile across. A hurricane's winds
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- may cover an area 60 miles wide out from the center of the eye. Another
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- reason is tornadoes rarely last as long as an hour, or travel more than
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- 100 miles. However , a hurricane may rage for a week or more (example:
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- Hurricane Dorthy) In that time, it may travel tens of thousands of miles
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- over the sea and land.
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- At sea, hurricane winds whip up giant waves up to 20 feet high. Such
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- waves can tear freighters and other oceangoing ships in half. Over land,
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- hurricane winds can uproot trees, blow down telephone lines and power
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- lines, and tear chimneys off rooftops. The air is filled with deadly
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- flying fragments of brick, wood, and glass.
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