1. Education
Send to a Friend via Email
You can opt-out at any time. Please refer to our privacy policy for contact information.

Tropical Depressions

By

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
  1. About.com
  2. Education
  3. Weather
  4. Weather Glossary
  5. T
  6. Tropical Depressions - Tropical Weather