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    Beaufort Scale of Wind Force      
      

Beaufort Knots* Km/hour M/S Description
0 <1 <1 <0.3 Calm
1 1-3 1-6 0.3-1.7 Light air
2 4-6 7-12 1.9-3.3 Light breeze
3 7-10 13-19 3.4-5.3 Gentle breeze
4 11-16 20-30 5.4-8.3 Moderate breeze
5 17-21 31-39 8.4-10.8 Fresh breeze
6 22-27 40-50 10.9-13.9 Strong breeze
7 28-33 51-62 14.0-17.2 Near breeze
8 34-40 63-74 17.3-20.5 Gale
9 41-47 75-87 Strong gale
10 48-55 88-102 Storm
11 56-63 103-117 Violent storm
12 >=64 >=118 Hurricane


* Equivalent speed at 10m above ground.
1 Km/hour = 0.54 Knots  ( or / 2 )
1 m/s       = 1.94 Knots    
Wind speed / direction symbols used on synoptic charts         

Specifications For Use At Sea And On Land               

Beaufort    Specifications   
0    Sea: Sea like a mirror.           
"Land: Calm, smoke rises vertically."           
1              Sea: Ripples with the appearance of scales formed but without foam crests
Land: Direction of wind shown by smoke drift but not by wind vanes.           
2 "Sea: Small wavelets, still short but more pronounced; crests have a glassy appearance and do not break."           
Land: Wind felt on face; leaves rustle; ordinary vane moved by wind.           
3 Sea: Large wavelets; crests begin to break; foam of glassy appearance; perhaps scattered white horses.           
Land: Leaves and small twigs in constant motion; wind extends light flag           
4 "Sea: Small waves, becoming longer; fairly frequent white horses."           
Land: Raises dust and loose paper; small branches moved.
5 "Sea: Moderate waves, taking a more pronounced long form; many white horses are formed; chance of some spray."
Land: Small trees in leaf begin to sway;  crested wavelets form on inland waters.
6 Sea: Large waves begin to form; the white foam crests are more extensive everywhere; probably some spray
Land: Large branches in motion; whistling heard in telegraph wires; umbrellas used with difficulty.
7 Sea: Sea heaps up and white foam from breaking waves begin to be blown in streaks along the direction of the wind
Land: Whole trees in motion; inconvenience felt when walking against wind.
8 Moderately high waves of greater length; edges of crests begin to breakinto spindrift. The foam is blown in well-marked streaks along the direction of the wind.
Land: Breaks twigs off trees, generally impedes progress.
9 Sea: 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.
Land: Slight structural damage occurs (chimney-pots and slates removed).
10 Sea: 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 a white appearance; the tumbling of the sea becomes heavy and shock-like; visibility affected.
Land: Seldom experienced inland; trees uprooted; considerable structural damage occurs.
11 Sea: 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.
Land: Very rarely experienced; accompanied by widespread damage.
12 Sea: The air is filled with foam and spray; sea completely white with driving spray; visibility very seriously affected.
Land: -