Beaufort Scale
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WebStation Australia
| Beau- fort No |
Description |
Cyclone category |
Average wind speed (Knots) |
Average wind speed (kilometres per
hour) |
Specifications for estimating speed
over land |
Specifications for estimating speed
over water |
| 0 |
Calm |
|
Less than 1 |
less than 1 |
Calm, smoke rises vertically. |
Sea like mirror |
| 1 |
Light Air |
|
1 - 3 |
1 - 5 |
Direction of wind shown by smoke
drift, but not by wind vanes. |
Ripples with the appearance of scales
are formed, but without foam crests |
| 2 |
Light breeze |
|
4 - 6 |
6 - 11 |
Wind felt on face; leaves rustle;
ordinary wind vane moved by wind. |
Small wavelets, still short, but more
pronounced; crests have a glassy appearance and do not break |
| 3 |
Gentle breeze |
|
7 - 10 |
12 - 19 |
Leaves and small twigs in constant
motion; wind extends light flag. |
Large wavelets; crests begin to break;
foam of glassy appearance; perhaps scattered white horses |
| 4 |
Moderate breeze |
|
11 - 16 |
20 - 28 |
Raises dust and loose paper; small
branches moved. |
Small waves, becoming longer; fairly
frequent white horses |
| 5 |
Fresh breeze |
|
17 -21 |
29 - 38 |
Small trees in leaf begin to sway;
crested wavelets form on inland waters. |
Moderate waves, taking a more
pronounced long form; many white horses are formed (chance of some
spray) |
| 6 |
Strong breeze |
|
22 - 27 |
39 - 49 |
Large branches in motion; whistling
heard in telegraph wires; umbrellas used with difficulty. |
Large waves begin to form; the white
foam crests are more extensive everywhere (probably some spray) |
| 7 |
Near gale |
|
28 - 33 |
50 - 61 |
Whole trees in motion; inconvenience
felt when walking against the wind. |
Sea heaps up and white foam from
breaking waves begins to be blown in streaks along the direction of
the wind |
| 8 |
Gale |
Category 1 |
34 - 40 |
62 - 74 |
Breaks twigs off trees; generally
impedes progress. |
Moderately high waves of greater
length; edges of crests begin to break into the spindrift; the foam is
blown in well-marked streaks along the diection of the wind |
| 9 |
Strong gale |
Category 1 |
41 - 47 |
75 - 88 |
Slight structural damage occurs
(chimney pots and slates removed). |
High waves; dense streaks of foam
along the direction of the wind; crests of waves begin to topple,
tumble and roll over; spray may affect visibility |
| 10 |
Storm |
Category 2 |
48 - 55 |
89 - 102 |
Seldom experienced inland; trees
uprooted; considerable structural damage occurs. |
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 a white appearance; the tumbling of the sea becomes
heavy and shock-like; visibility affected |
| 11 |
Violent storm |
Category 2 |
56 - 63 |
103 - 117 |
Very rarely experienced; accompanied
by widespread damage. |
Exceptionally high waves (small and
medium sized 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 |
| 12 |
Hurricane |
Category 3,4,5 |
64 and over |
118 and over |
Severe and extensive damage. |
The air is filled with foam and spray;
sea completely white with driving spray; visibility very seriously
affected |