Hurricanes

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.