Scala di Beaufort
The scale was devised in 1806 by the British naval Commander, later Admiral, Sir Francis Beaufort.
| Number | Knots | Wind name | At sea | On land |
|---|---|---|---|---|
| 0 | 0-1 | Calm | Sea like a mirror | Smoke rises vertically |
| 1 | 1-3 | Light Air | Ripples with the appearance of scales are formed but without foam crests | Direction of wind shown by smoke drift, but not by vanes |
| 2 | 4-6 | Light Breeze | Small wavelets, still short but more pronounced; crests have a glassy appearance and do not break | Wind felt on face; leaves rustle; ordinary vane moved by wind |
| 3 | 7-10 | Gentle Breeze | Large wavelets; crests begin to break; foam of glassy appearance; perhaps scattered white horses | Leaves and small twigs in constant motion; wind extends light flag |
| 4 | 11-16 | Moderate Breeze | small waves, becoming longer; fairly frequent white horses | Raises dust and loose paper; small branches are moved |
| 5 | 17-21 | Fresh Breeze | Moderate waves taking a more pronounced long form; many white hourses are formed; chance of some spray | Small trees in leaf begin to sway; crested wavelets form on inland waters |
| 6 | 22-27 | Strong Breeze | Large waves begin to form; the white foan crests are more extensive everywhere; probably some spray | Large branches in motion; whistling heard in telegraph wires; umbrellas used with dificulty |
| 7 | 28-33 | Near Gale / Moderate Gale | Moderately high waves of greater length; edges crests begin to break into spindrift; the foam is blown in well-marked streaks along the direction of the wind | Whole trees in motion; inconvenience felt when walking against wind |
| 8 | 34-40 | Gale / Fresh Gale | Moderately high waves of greater length; edges crests begin to break into spindrift; the foam is blown in well-marked streaks along the direction of the wind | Breaks twigs off trees; generally impedes progress |
| 9 | 41-47 | Strong Gale | High waves; dense streaks of foam along the direction of wind; crests of waves begin to topple, tumble and roll over; spray may affect visibility | Slight structural damage occurs (chimney post and slates removed) |
| 10 | 48-55 | Storm / Whole Gale | Very high waves with long overhanging crests; 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; tumbling of the sea becomes heavy and shock-like; visibility affected | Seldom experienced inland; trees uprooted; considerable structural damage occurs |
| 11 | 56-63 | Violent Storm / Storm | Exceptionally high waves (small and medium size ships might be for a time lost from view behind waves); sea is completely covered with long white patches of foam lying along the direction of wind; everywhere the edges are blown into froth; visibility afected | Very rarely experienced; accompanied by widespread damage |
| 12 | 64 and greater | Hurricane | he air is filled with foam and spray; sea completely white with driving spray; visibility very seriously affected | Very rarely experienced; accompanied by widespread damage |
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