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The Beaufort Scale is used worldwide to describe the force of the
wind. Developed in 1805 by Admiral Sir Francis Beaufort the scale was designed to gauge
the wind speed through observations of the sea state. The scale starts at 0 (calm) and goes to 12 (hurricane), the land state
equivalents were added at a later stage.
|
| Force |
Speed |
Description |
Sea state |
Land state |
|
miles
|
knots |
|
|
|
|
| 0 |
0-1 |
0-1 |
Calm |
Sea like a mirror |
Calm; smoke rises vertically |
| 1 |
1-3 |
1-3 |
Light air |
Ripple with the appearance of scales
are formed but without foam crests |
Direction of wind shown by smoke drift,
but not by wind vanes |
| 2 |
4-7 |
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 vanes moved by wind |
| 3 |
8-12 |
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 |
13-18 |
11-16 |
Moderate breeze |
Small waves, becoming larger; fairly
frequent white horses |
Raises dust and loose paper; small
branches are moved |
Top of page
Beaufrot Scale continued below
|
| Force |
Speed |
Description |
Sea state |
Land state |
|
miles
|
knots |
|
|
|
|
| 5 |
19-24 |
17-21 |
Fresh breeze |
Moderate waves, taking a 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 |
| 6 |
25-31 |
22-27 |
Strong breeze |
Large waves begin to form; the white foam crests
are more extensive everywhere. Probably some spray |
Large branches in motion; inconvenience felt when
walking against the wind |
| 7 |
32-38 |
28-33 |
Near gale |
Sea heaps up and white foam from breaking waves
begins to be blown in streaks along the direction of the wind |
Whole trees in motion; whistling heard in telegraph
wires; umbrellas used with difficulty |
| 8 |
39-46 |
34-40 |
Gale |
Moderately high waves of greater length; edges of
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 |
Top of page
Beaufrot Scale continued below
|
| Force |
Speed |
Description |
Sea state |
Land state |
|
miles
|
knots |
|
|
|
|
| 9 |
47-54 |
41-47 |
Severe gale |
High waves. Dense streaks of foam along the
direction of the wind. Crests of waves begin to topple, tumbel and roll over. Spray may
affect visibility |
Slight structural damage occurs (chimney-pots and
slates removed) |
| 10 |
55-63 |
48-55 |
Storm |
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 on a white appearance. The 'tumbling'
of the sea becomes heavyand shock-like. Visibility affected |
Seldom experienced inland; trees uprooted;
consicerable structural damage occurs |
| 11 |
64-72 |
56-63 |
Violent storm |
Exceptionally high waves (small and medium-size
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 |
Very rarely experienced; accompanied by widespread
damage |
| 12 |
73-83 |
64-71 |
Hurricane |
The air is filled with foam and spray. Sea
completely white with driving spray; visibility very seriously affected
|
|
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