| Beaufort Force |
General Description |
Sea Criterion |
Land Criterion |
Windspeed in knots |
| 0 |
Calm |
Sea like a mirror |
Calm; smoke rises vertically |
below 1 |
| 1 |
Light air |
Ripples with appearance of scales are formed but without foam crests |
Wind direction shown bvsmoke drift but not by windvanes |
1 to 3 |
| 2 |
Light breeze |
Small wavelets, still short but more pronounced. Crests have a glassy appearance and do not break |
Wind felt on face; leavesrustle; ordinary vane moved by wind |
4 to 6 |
| 3 |
Gentle breeze |
Large wavelets. Crests begin to break. Foam of glassy appearance. Perhaps scattered white horses |
Leaves and small twigs in constant motion. Windextends light flags |
7 to 10 |
| 4 |
Moderate breeze |
Small waves becoming longer; fairly frequent white horses |
Raises dust and loose paper;small branches are moved |
11 to 16 |
| 5 |
Fresh breeze |
Moderate waves, taking more pronounced long form; many white horses are formed. Chance of some spray |
Small trees in leaf begin to sway. Crested wavelets form on inland waters |
17 to 21 |
| 6 |
Strong breeze |
Large waves begin to form; white foam-crests are more extensive everywhere. Probably some spray |
Large branches in motion;whistling heard in telephonewires, umbrellas used withdifficulty |
22 to 27 |
| 7 |
Near gale |
Sea heaps up and white foam from breaking waves begin to be blown in,,streaks along the direction of the wind |
Whole trees in motion; inconvenience felt when walking against wind |
28 to 33 |
| 8 |
Gale |
Moderately high waves of greater length; edges of crests begin to break into spin-drift. The foam is blown in well- marked streaks along the direction of the wind |
Breaks twigs off trees;generally impedes progress |
34 to 40 |
| 9 |
Severe gale |
High waves. Dense streaks of foam along the direction of the windCrests of waves begin to topple, tumble and roll over. Spray may affect visibility Spray may affect visibility |
Slight structural damageoccurs (chimney pots and slates removed) |
41 to 47 |
| 10 |
Storm |
Very high waves with long overhanging crest. Resulting foam in great patches is blown in dense streaks along the direction of the wind. Whole surface takes on a white appearance.Tumbling of sea becomes heavy and shock-like.Visibility affected. |
Seldom experienced inland; trees uprooted; considerable structural damage occurs |
48 to 55 |
