The Beaufort Scale of Wind Forces
The Beaufort Scale reflects both wind strength and sea conditions. Developed in 1805 by Admiral Sir Francis Beaufort of the British Navy. The scale divides wind and sea conditions into 12 "Forces" ranging from calm to hurricane. It describes typical conditions offshore in large bodies of water.
|
Beaufort Number or
Force |
Wind Speed and
Description |
Effects Land/Sea |
Probable Wave
Height |
||
|
MPH |
Knots |
Description |
|||
|
0 |
<1 |
<1 |
Calm |
Still, calm air, smoke will rise vertically. Smooth like a
mirror. |
0 |
|
1 |
1-3 |
1-3 |
Light Air |
Rising smoke drifts, wind vane is inactive. Small ripples like
fish scales. |
¼ - ½ foot |
|
2 |
4-7 |
4-6 |
Light Breeze |
Leaves rustle, can feel wind on your face, wind vanes begin to
move. Short, small pronounced wavelets with no crests. |
¼ - ½ foot |
|
3 |
8-12 |
7-10 |
Gentle Breeze |
Leaves and small twigs move, light weight flags extend. Large
wavelets, crests start to break, some whitecaps. |
2 feet |
|
4 |
13-18 |
11-16 |
Moderate Breeze |
Small branches move, raises dust, leaves and paper. Small
waves develop, becoming longer, whitecaps. |
4 feet |
|
5 |
19-24 |
17-21 |
Fresh Breeze |
Small trees sway. Moderate lengthening waves, with many white
caps and some spray. |
6 feet |
|
6 |
25-31 |
22-27 |
Strong Breeze |
Large tree branches move, telephone wires begin to
"whistle"Large waves, extensive white caps, some spray. |
10 feet |
|
7 |
32-38 |
28-33 |
Near Gale |
Large trees sway, becoming difficult to walk. Heaps of waves,
with some breakers whose foam is blown downwind in streaks. |
14 feet |
|
8 |
39-46 |
34-40 |
Gale |
Twigs and small branches are broken from trees, walking is
difficult. Moderately large waves with blown foam. |
18 feet |
|
9 |
47-54 |
41-47 |
Strong Gale |
Slight damage occurs to buildings, shingles are blown off of
roofs. Rolling seas, dense foam, Blowing spray reduces visibility. |
23 feet |
|
10 |
55-63 |
48-55 |
Whole Gale or Storm |
Trees are broken or uprooted, building damage is considerable.
Very high waves with long, overhanging crests. The sea looks white,
visibility is greatly reduced. |
29 feet |
|
11 |
64-72 |
56-63 |
Violent Storm |
Extensive widespread damage. Wave edges are blown into froth,
and the sea is covered with patches of foam. |
37 feet |
|
12 |
73+ |
64+ |
Hurricane |
Extreme destruction, devastation. The air is filled with foam
and spray, and the sea is completely white, little visibility. |
45 feet |