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| Hurricane Elena of 1985, a Strong Hurricane |
The Basics
A hurricane is one of nature's most awesome forces. Scientists at the National Center for Atmospheric Research estimate that
a hurricane releases heat energy at the rate of 50 to 200 trillion watts - about the amount of energy released by exploding
a 10-megaton nuclear bomb every 20 minutes. Hurricanes are found all over the world, and are not always called hurricanes.
In the North Pacific Ocean hurricanes are called Typhoons, and in the South Pacific and South Indian Ocean they are called
Cyclones. Whatever the name, a storm must have winds greater than 73 mph to be classified as a hurricane.
The Mechanics
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| Impressive Outer Bands of Hurricane Katrina |
A hurricane is basically a large storm, relatively speaking. Hurricanes are powered by warm water, and moist air, which is
why they are found in tropical areas. Hurricanes are a large, rotating system of clouds and thunderstorms which can cause
tremendous damage, the clouds from the hurricane eventually form outer spiral bands as the storm becomes stronger. This is
called outflow, and helps the storm grow in size and strength acting as a chimney for the storm. The outflow releases the
dry air that the hurricane stripped the moisture of. Without this release, the hurricane would not be able to thrive. These
high outer bands and clouds give the hurricane its swirling appearance. Moist air is critical in maintaining a powerful hurricane.
The outer bands are generally able to keep dry air from entering the circulation, but when dry air is able to wrap its way
into the eye, the hurricane is in trouble. When the dry air enters the eye, it destroys the storms, and weakens the storm.
Without convection near the eye, the winds die down and the hurricane weakens.
The Eye
The eye of the storm is the calm center of the storm, which is usually calm and sometimes completely cloud free. Stronger
hurricanes tend to have larger eyes, and some weak hurricanes never develop a clear and distinct eye. The eye is the area
of sinking air inside the storm and is the center of cirulation. Eyes of hurricanes range greatly in size, sometimes as large
as 125 miles in diameter. Hurricane Wilma of 2005 had one of the smallest eyes ever recorded, due to the incredibly rapid
intensification. The eye later widened as Wilma underwent eyewall replacement cycles. Although the eye is the calmest area
of the storm, just outside the eye is the powerful eyewall; which is where the worst of the storm is found. The eyewall is
the strongest convection of the storm, wrapped around the eye. This is where the highest winds, heaviest rains, and most powerful
convection of the storm is found. Most damages by hurricanes are caused when the eyewall passes over land. In strong hurricanes,
the eyewall is very symmetrical, wrapping completely around the eye. In weaker storms, the eyewall may not even exist and
may be unevenly distributed around the eye. This is sometimes due to wind shear which blows the storm out of proportion, restricting
thunderstorms in certain areas. When the outerbands begin to gather intense convection, robbing the center of such, this is
known as an eyewall replacement cycle and usually weakens the storm temporarily. The outer eyewall eventually replaces the
inner eyewall, usually resulting in a larger sized eye.
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