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

Category: Science