sustained winds between 50 and 87 km/h

A gale is a very strong wind. The Beaufort scale is a way to measure weather conditions. It is based on observations. The first level of the scale that uses the word gale is 7 beaufort (of a total of 13 steps). There are other definitions as well. The U.S. Government's National Weather Service defines a gale as 34 to 47 knots (63 km/h to 87 km/h or 39 miles per hour to 54 miles per hour) of sustained surface winds.[1] Forecasters usually issue gale warnings when they think there will be winds of this strength.

7 beaufort is the first level where the word gale is used

Other sources use speeds as low as 28 knots (52 km/h) and as high as 90 knots (170 km/h). The 90-knot (170 km/h) definition is rare. A common alternative definition of the maximum is 55 knots (102 km/h).[2]