A special marine warning ( SAME code SMW) is a warning issued by the U.S.

National Weather Service The National Weather Service (NWS) is an Government agency, agency of the Federal government of the United States, United States federal government that is tasked with providing weather forecasts, warnings of hazardous weather, and other weathe ...

for potentially hazardous marine weather conditions usually of short duration (up to 2 hours) producing sustained marine thunderstorm winds or associated gusts of 34 knots or greater; or hail 3/4 inch or more in diameter; or waterspouts affecting areas included in a coastal waters forecast, a nearshore marine forecast, or a Great Lakes open lakes forecast that is not adequately covered by existing marine warnings. It is also used for short duration mesoscale events such as a strong cold front, gravity wave, squall line, etc., lasting less than 2 hours and producing winds or gusts of 34 knots or greater.

References

Weather warnings and advisories {{meteorology-stub