A TROPICAL DISTURBANCE is the first stage of development of a hurricane.
It consists of a mass of
thunderstorms that have only a slight wind circulation.
The tropical disturbance becomes a tropical depression when the winds increase to more than 20 knots
or 23 miles per hour.
A TROPICAL DEPRESSION forms when a group of thunderstorms
comes together under the right atmospheric conditions for a certain length of time.
Winds near the center of the tropical depression are constantly between 20 and 34 knots (23 - 39 mph).
Lowered pressure is indicated with at least one closed
on a surface pressure chart. Also, the organized circulation of wind in the center of the thunderstorms
||This is a satellite picture of a tropical depression.
Tropical depressions look like individual thunderstorms that are grouped together.
A TROPICAL STORM forms when the maximum sustained winds have
intensified to between 35-64 knots (39-73 mph).
It becomes better organized and begins to look like a hurricane with a circular shape.
At this point, the storm is given a
Most of the problems from tropical storms come
from heavy rainfall.
|This is a satellite picture of tropical storm Charlie in 1998 over Texas.
This storm dumped between 5-10 inches of rain over many southern Texas cities.
A HURRICANE finally forms when surface pressures continue to drop and
when sustained wind speeds reach 64 knots (74 mph).
There is also a definite rotation about the
||Hurricanes have definite parts
that are easily recognized in this satellite animation.
Imax Movie-Fly Into a Hurricane
Listen to Max Mayfield who is
Deputy Director of the National Hurricane Center in
Miami, Florida as he gives a play-by-play account of the stages of a hurricane.
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