courtesy
of National Hurricane Center
A hurricane is a type of tropical cyclone-the
general term for all circulating weather systems
(counterclockwise in the Northern Hemisphere)
over tropical waters. Tropical cyclones are
classified as follows:
1.
Tropical Depression - An organized system
of clouds and thunderstorms with a defined
circulation and maximum sustained winds
of 38 mph (33 knots) or less.
2.
Tropical Storm - An organized system of
strong thunderstorms with a defined circulation
and maximum sustained winds of 39 to 73
mph (34-63 knots).
3.
Hurricane - An intense tropical weather
system with a well defined circulation and
maximum sustained winds of 74 mph (64 knots)
or higher. In the western Pacific, hurricanes
are called "typhoons," and similar
storms in the Indian Ocean are called "cyclones."
Hurricanes
are products of the tropical ocean and atmosphere.
Powered by heat from the sea, they are steered
by the easterly trade winds and the temperate
westerlies as well as by their own ferocious
energy. Around their core, winds grow with
great velocity, generating violent seas. Moving
ashore, they sweep the ocean inward while
spawning tornadoes and producing torrential
rains and floods. Each year on average, ten
tropical storms (of which six become hurricanes)
develop over the Atlantic Ocean, Caribbean
Sea, or Gulf of Mexico. Many of these remain
over the ocean. However, about five hurricanes
strike the United States coastline every 3
years. Of these five, two will be major hurricanes
(category 3 or greater on the Saffir-Simpson
Hurricane Scale).
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