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Tropical Depressions


In this satellite image provided by the National Oceanic and Atmospheric Administration (NOAA), tropical depression Gustav is seen over the United States on September 2, 2008.
Handout/Getty Images News/Getty Images
Definition: A tropical depression is a tropical cyclone with wind speeds of 33 knots (38 mph) or less. Once a tropical depression has wind speeds of 34 knots or greater, it is called a tropical storm. A tropical depression has evidence of organized winds and thunderstorms in contrast to a tropical wave or disturbance.

Sometimes, the media will confuse people by naming a tropical depression. This is usually a case where a storm did move up to a tropical storm strength, but later was downgraded back to a tropical depression. This can make some tropical depressions actually have a name. If the storm dissipates before becoming a true tropical storm, it will usually be given a number. For example – TD1 is a reference to Tropical Depression One.

Tropical depression naming is not a general practice around the world. One notable exception is in the Philippines which uses the Philippine Tropical Cyclone Names list in their area of responsibilty.

Also Known As: TD, depressions
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