Beaufort Wind Scale
Developed in 1805 by Sir Francis Beaufort of England
Scale Knots Wave Height Surroundings
Force 0
Calm
< 1 Knot 0 Sea is like a mirror
Force 1
Light Air
1-3 .25ft
(.1M)
Ripples with the appearance of scales, but without foam crests
Force 2
Light Breeze
4-6 .5-1ft
(.2-.3M)
Small wavelets, crests have a glassy appearance and do not break
Force 3
Gentle Breeze
7-10 2-3ft
(.6-1M)
Large wavelets, crests begin to break, any foam has a glassy appearance, scattered whitecaps
Force 4
Moderate Breeze
11-16 3.5-5ft
(1-1.5M)
Small waves becoming longer, fairly frequent white horses
Force 5
Fresh Breeze
17-21 6-8ft
(2-2.5M)
Moderate waves take more pronounced long form, many white horses, chance of some spray
Force 6
Strong Breeze
22-27 9.5-13ft
(3-4M)
Larger waves begin to form, spray is present, white foam crests are everywhere
Force 7
Near Gale
28-33 13.5-19ft
(4-5.5)
Sea heaps up, white foam from breaking waves begins to be blown in streaks along the wind direction
Force 8
Gale
34-40 18-25ft
(5.5-7.5M)
Moderately high waves of greater length, edges of crests begin to break into the spindrift, foam blown in well marked streaks along wind direction
Force 9
Strong Gale
41-47 23-32ft
(7-10)
High waves, dense streaks of foam along direction of wind, wave crests begin to topple, tumble and roll over, spray may affect visibility
Force 10
Storm
48-55 29-41ft
(9-12.5M)
Very high waves with very long overhanging crests, the resulting foam, in great patches, is blown in dense white streaks along wind direction. On the whole, sea surface takes a white appearance, tumbling of the sea is heavy and shock-like, visibility affected
Force 11
Violent Storm
56-63 37-52ft
(11.5-16M)
Exceptionally high waves, small to medium sized ships may be lost to view behind the waves. Sea completed covered with long white patches of foam lying along wind direction. Everywhere, the edges of waves crests are blown into froth
Force 12
Hurricane
64 > 53ft
(> 16M)
Sea completely white with driving spray, visibility very seriously affected. The air is filled with foam and spray

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