You are at: NWS Home » SRH Home » WFO Mobile Home » Tropical Weather Page » Tropical Definitions

Tropical Definitions
 Tropical Cyclone
      A tropical cyclone is a low pressure system not associated with a cold front,
      that develops over tropical and sometimes sub-tropical waters, and has an
      organized circulation.

   Tropical Depression
      A tropical depression is a tropical cyclone in which the maximum sustained
      surface winds (a one minute average) are 38 miles per hour (33 knots) or
      less. 

   Tropical Storm
      A tropical storm is a tropical cyclone in which the maximum sustained surface
      winds range from 39 to 73 miles per hour (34 to 63 knots). The number of
      Tropical Storms and Hurricanes increases substantially in August, peaks in
      mid-September, and decreases towards a minimum by early November.
   
   Hurricane
      A hurricane is a tropical cyclone in which the maximum sustained surface
      winds are 74 miles per hour or greater (64 knots or greater).

   Tropical Storm Watch
      A Tropical Storm Watch is issued when Tropical Storm conditions, including
      winds from 39 to 73 miles per hour, pose a possible threat to a specified
      coastal area within 48 hours.

   Tropical Storm Warning
      A Tropical Storm Warning is issued when Tropical Storm conditions, including
      winds of from 39 to 73 miles per hour, are expected in a specified coastal 
      area within 36 hours or less.

   Hurricane Watch
      A Hurricane Watch is issued for a specified coastal area for which a hurricane
      a or an incipient hurricane condition is a possible threat within 48 hours. 

   Hurricane Warning
      A Hurricane Warning is issued when sustained wind of 74 miles per hour or
      higher, caused by a hurricane, are expected in a specified coastal area in
      36 hours or less.
      
      A Hurricane Warning can remain in effect when dangerously high water or a
      combination of dangerously high water and exceptionally high waves continues,
      even though the winds may have subsided below hurricane intensity.   

USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.