National Weather Service United States Department of Commerce

Marine Definitions

Gale Warning: A warning of sustained winds in the range 34 to 47 knots (KT) inclusive either predicted or occurring not associated with tropical cyclones.

Gust: A rapid fluctuation of wind speed with variations of 10 KT or more between peaks and lulls.

Hurricane Warning: A warning issued by the National Hurricane Center (also known as the Tropical Prediction Center) for sustained winds of 64 KT or greater either predicted or occurring associated with a tropical cyclone.

Knot: Unit of speed used in navigation, equal to 1 NM per hour or about 1.15 statute miles per hour.

Marine Weather Statement: A product to provide mariners with details on significant or potentially hazardous conditions not otherwise covered in existing marine warnings and forecasts.

Nautical Mile: Unit of distance used in marine navigation, equal to approximately 1.15 statute miles (length of 1 minute of latitude).

Significant Wave Height

Small Craft Advisory: An advisory in coastal waters for winds from 20 to 33 KT inclusive and/or for seas, either predicted or occurring, that are considered potentially hazardous to small boats. At the Key West office we use 7 feet or greater as the threshold. However, there is no legal definition for "small craft."

Special Marine Warning: A severe local storm warning affecting coastal water areas, or a warning of potentially hazardous weather conditions usually of short duration (2 hours or less) and producing wind speeds of 34 KT or more that is not adequately covered by existing marine warnings. Also, this product is issued for waterspouts, either predicted or occurring.

Storm Warning: A warning of sustained winds of 48 KT or more, either predicted or occurring, not associated with tropical cyclones.

Sustained Wind: The wind speed obtained by averaging observed values over a period of at least 1 minute.

Swell: Wind-generated waves that have traveled out of their generating area. Swells characteristically exhibit smoother, more regular and uniform crests and a longer period than wind waves.

Tropical Storm Warning: A warning of sustained winds from 34 to 63 KT inclusive either predicted or occurring, associated with tropical cyclones.

Waterspout: A rotating column of air, usually pendant from a cumulus or cumulonimbus cloud, that forms over water and whose circulation extends to the surface.