Beaufort Wind Scale
The Beaufort Scale was originally developed as a system for estimating wind strengths without the use of instruments. It was introduced in 1806 by Admiral Sir Francis Beaufort (1774-1857) of the British navy to describe wind effects on a fully rigged man-of-war sailing vessel, and it was later extended to include descriptions of effects on land features as well.
Force | Description | Conditions Ashore | Conditions Afloat | Wind speed (knots) |
---|---|---|---|---|
0 | Calm | Smoke rises vertically | Sea like a mirror | 0 |
1 | Light air | Smoke drifts | Ripples Only | 1-3 |
2 | Light breeze | Leaves rustle; vane moved by wind | Small wavelets not breaking | 4-6 |
3 | Gentle breeze | Leaves in constant motion; light flag extend | Large wavelets, crests begin to break | 7-10 |
4 | Moderate breeze | Raises dust and loose paper; small branches move | Small waves growing longer, fairly frequent white horses | 11-16 |
5 | Fresh breeze | Small trees sway; crested wavelets on inland water | Moderate waves taking more pronounced form; many white horses, perhaps some spray | 17-21 |
6 | Strong breeze | Large branches in motion; whistling in telegraph | Large waves forming; white foam crests more extensive, probably some spray | 22-27 |
7 | Near gale | Whole trees in motion | Sea heaps up; white foam streaks begin blowing from crests; very rough | 28-33 |
8 | Gale | Breaks twigs off trees; impedes walking | Moderatly high waves of greater length;crests break into spindrift with foamy streaks | 34-40 |
9 | Severe gale | Slight structural damage to buildings | High waves with tumbling crests; dense streaks of foam; spray may affect visibility | 41-47 |
10 | Storm | Large branches broken; some trees uprooted | Very high waves with long overhanging crests and dense streaks of foam making surface of the sea white; heavy tumbling sea | 48-55 |
11 | Violent Storm | Very rarely experienced inland, widespread damage caused | Exceptionally high waves; sea completly covered with long white patches of foam along direction of wind | 56-63 |
12 | Hurricane | Very widespread damage | Air filled with foam and spray; sea white with driving spray; visibility very seriously affected | 64+ |