Beaufort scale

The Beaufort scale is an empirical wind force scale from 0 to 12 that ties a force number to a wind speed band and to the appearance of the sea surface. Devised by Francis Beaufort in 1805 and standardized by the WMO, it runs from force 0 (calm, under 1 knot) through force 8 (gale, 34 to 40 knots) and force 10 (storm, 48 to 55 knots) to force 12 (hurricane, 64 knots and above). Each step lets the navigator estimate true wind speed from sea state alone when no anemometer reading is available, and log it in a common code. Forecasts and synoptic charts still report wind in Beaufort force.