A gale is a very strong wind. There are conflicting definitions of how strong a wind must be to be considered a gale. The U.S. National Weather Service defines a gale as 34–47 knots (63–87 km/h, 17.5–24.2 m/s or 39–54 miles/hour) of sustained surface winds. Forecasters typically issue gale warnings when winds of this strength are expected.
Other sources use minima as low as 28 knots (52 km/h, 32 mph) and maxima as high as 90 knots (170 km/h, 100 mph). Through 1986, the National Hurricane Center used the term gale to refer to winds of tropical force for coastal areas, between 33 knots (61 km/h, 38 mph) and 63 knots (117 km/h, 72 mph). The 90-knot (170 km/h) definition is very non-standard. A common alternative definition of the maximum is 55 knots (102 km/h, 63 mph).
The most common way of measuring winds is with the Beaufort scale, which defines a gale as wind from 50 to 102 km/h. It is an empirical measure for describing wind speed based mainly on observed sea conditions. Its full name is the Beaufort Wind Force Scale.
On the Beaufort Wind Scale, a gale is classified as: 7: Moderate Gale (32–38 miles per hour), 8: Fresh Gale (39-46 mph), 9: Strong Gale (47-54 mph) and 10: Storm/Whole Gale (55-63 mph). A gale is a type of Wind Description preceded by 0: Calm, 1: Light Air, 2: Light Breeze, 3: Gentle Breeze, 4: Moderate Breeze, 5: Fresh Breeze, 6: Strong Breeze and succeeded by 11: Violent Storm and 12: Hurricane on a Beaufort Wind Scale. There is a unique Beaufort Scale number and a unique Arrow Indication for each type of Wind Description mentioned above.
The word gale is derived from the older gail, but its origin is uncertain.