What does a “Gale Warning” mean?

The National Weather Service has developed a multi-tier concept for forecasting hazardous weather which includes outlooks, watches, warnings and advisories.  Below are the visual day flag and nighttime light signals that warn of rough weather.  NOAA discontinued using the flags in 1989, however, the Coast Guard reestablished them in 2007 at selected small boat stations across the country. http://www.nws.noaa.gov/om/marine/cwd.htm

NOAA Coastal Warning Display System

An outlook is issued to indicate that a hazardous weather or hydrologic event may occur over the next several days. 

A watch is issued whenever that risk has increased significantly but the occurrence, location or timing are still uncertain. Marine Watches for “GALE” “STORM”, and “HURRICANE FORCE” wind conditions, not related to tropical cyclones, can be highlighted in extended range forecasts beyond 24-hours for coastal inland waters, and offshore waters (does not include high seas forecasts). 

A warning is issued when the hazardous condition or event is either occurring, imminent or likely (for the marine forecasts, within 24-hours). 

A weather advisory is issued when a hazardous weather condition or event is occurring, imminent or likely but for less serious conditions than those that would warrant a warning. 

A Gale Warning  is issued when sustained surface winds (averaged over a ten minute period, momentary gusts may be higher) of 34 knots (39 mph) to 47 knots (54 mph) are either occurring, imminent or likely (for the marine forecasts, within 24-hours). 

“Developing Gale” refers to an extratropical low or an area in which gale force winds of 34 knots (39 mph) to 47 knots (54 mph) are “expected” by a certain time period. On surface analysis charts, a “DEVELOPING GALE” label indicates gale force winds within the next 24 hours. When the label is used on the 48 hour surface forecast and 96 hour surface forecast charts, gale force winds are expected to develop by 72 hours and 120 hours, respectively.

NOAA OPC Surface Analysis Chart

 Fred Pickhardt, chief meteorologist,
Ocean Weather Services
http://www.oceanweatherservices.com