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Hurricane,
name applied to migratory tropical cyclones that originate
over oceans in certain regions near the equator, and
particularly to those arising in the West Indian region,
including the Caribbean Sea and the Gulf of Mexico.
Hurricane-type cyclones in the western Pacific are known
as typhoons.
Most hurricanes
originate within the doldrums, a narrow equatorial belt
characterized by intermittent calms, light variable
breezes, and frequent squalls, and lying between the
northeast and southeast trade winds
. As the doldrums of the
Atlantic are situated largely to the north of the equator,
hurricanes do not occur in the South Atlantic Ocean. The
Pacific doldrums extend north and south of the equator;
thus hurricanes occur in the South and North Pacific
oceans.
Hurricanes consist of
high-velocity winds blowing circularly around a
low-pressure center, known as the eye of the storm. The
low-pressure center develops when the warm, saturated air
prevalent in the doldrums is under run and forced upward
by denser, cooler air. From the edge of the storm toward
its center, the atmospheric pressure drops sharply and the
wind velocity rises. The winds attain maximum force close
to the point of lowest pressure (about 724 torr, or about
28.5 in. of mercury). The diameter of the area affected by
winds of destructive force may exceed 240 km (150 mi).
Gale winds prevail over a larger area, averaging 480 km
(300 mi) in diameter. The strength of a hurricane is rated
from 1 to 5. The mildest, Category 1, has winds of at
least 120 km/h (74 mph). The strongest (and rarest),
Category 5, has winds that exceed 250 km/h (155 mph).
Within the eye of the storm, which averages 24 km (15 mi)
in diameter, the winds stop and the clouds lift, but the
seas remain very violent.
Hurricanes
generally move in a path resembling the curve of a
parabola. In the northern hemisphere the storms usually
travel first in a northwesterly direction and in the
higher latitudes turn toward the northeast. In the
southern hemisphere the usual path of the hurricane is
initially to the southwest and subsequently to the
southeast. Hurricanes travel at varying rates. In the
lower latitudes the rate ranges from 8 to 32 km/h (5 to 20
mph) and in the higher latitudes it may increase to as
much as 80 km/h (50 mph). Those areas in which the
hurricane winds blow in the same direction as the general
movement of the storm are subjected to the maximum
destructive violence of the hurricane.
This
information has brought it to you from Encarta 2002
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