Download How Hurricanes Form - hrsbstaff.ednet.ns.ca

How Hurricanes Form
A tropical thunderstorm can grow into a massive hurricane under certain
conditions. Sometimes several thunderstorms start rotating around a central
area of low pressure. This is called a tropical depression. If the depression
strengthens so that winds reach at least 39 mph, it is called a tropical storm.
And if wind speeds increase to more than 74 mph, it is called a tropical
cyclone or hurricane.
Once formed, hurricanes take energy from the warm ocean water to become
stronger. A storm will strengthen if there is a supply of warm, moist air to
feed it. Warm, moist air is found above warm, tropical ocean waters. While a
hurricane is over warm water it will continue to grow. A hurricane dies
when it moves away from the tropics. When a hurricane moves into areas
with cooler ocean water, it weakens. It will also weaken if it travels over
land.
The rotation of the storm is due to the Coriolis Effect, a product of the
Earth's rotation. This causes the air being drawn into the central low pressure
to curve. The air rises as it rotates. This rising air, which is saturated with
water, cools and condenses, forming clouds. Hurricanes do not occur within
300 miles (500 kilometers) of the equator because there is no Coriolis Effect
at the equator.
Hurricanes form in the tropics over warm ocean water and die down when
they move over land or out of the tropics. These storms are called hurricanes
in the Atlantic and typhoons or tropical cyclones in other areas of the world.
In the Northern Hemisphere the storms
rotate counterclockwise and in the
Southern Hemisphere they rotate
clockwise because of the Coriolis Effect.
At the center of the rotating storm is a
small area of calm weather and clear skies
called the eye.
A hurricane needs five things:
Taken from
http://www.windows2universe.org/earth/Atmosphere/hurric
ane/formation.html , September 3, 2010