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Header of Beaufort Wind Scale
Descriptive term Beaufort scale number Mean velocity in knots Mean velocity in metre per second Sea criterion Probable height of waves in metres Probable maximum height of waves in metres
Calm 0 <1 <0.5 Sea like a mirror. - -
Light 1 1-3 0.5-1.5 Ripples with the appearance of scales are formed but without foam crests. 0.1 0.1
Light 2 4-6 2-3 Small wavelets, still short but more pronounced; crests have a glassy appearance and do not break. 0.2 0.3
Moderate 3 7-10 3.5-5 Large wavelets; crests begin to break; foam of glassy appearance; perhaps scattered white horses. 0.6 1
Moderate 4 11-16 5.5-8 Small waves, becoming longer; fairly frequent white horses. 1 1.5
Fresh 5 17-21 8.5-11 Moderate waves, taking a more pronounced long form; many white horses are formed (chance of some spray). 2 2.5
Strong 6 22-27 11.5-14 Large waves begin to form; the white foam crests are more extensive everywhere (probably some spray). 3 4
Strong 7 28-33 14.5-17 Sea heaps up and white foam from breaking waves begins to be blown in streaks along the direction of the wind. 4 5.5
Gale 8 34-40 17.5-20.5 Moderately high waves of greater length; edges of crests begin to break into spindrift; the foam is blown in well-marked streaks along the direction of the wind. 5.5 7.5
Gale 9 41-47 21-24 High waves; dense streaks of foam along the direction of the wind; crests of waves begin to topple, tumble and roll over; spray may affect visibility. 7 10
Storm 10 48-55 24.5-28.5 Very high waves with long overhanging crests; the resulting foam, in great patches, is blown in dense white streaks along the direction of the wind; on the whole, the surface of the sea takes on a white appearance; the tumbling of the sea becomes heavy and shocklike; visibility affected. 9 12.5
Storm 11 56-63 29-32.5 Exceptionally high waves (small and medium-sized ships might be for a time lost to view behind the waves); the sea is completely covered with long white patches of foam lying along the direction of the wind; everywhere the edges of the wave crests are blown into froth; visibility affected. 11.5 16
Hurricane 12 64 and over 33 and over The air is filled with foam and spray; sea completely white with driving spray; visibility very seriously affected. 14 or over -
Last revision date: <18 Dec 2012>