| Specification and speeds |
Equivalent
speed at 10 m
above sea level |
|
| Mean |
Limits |
Description
in forecasts |
State
of
sea |
Probable
height of waves* metres |
| Force |
Description |
Specification for use
at sea* |
knots |
metres
per second
|
knots |
metres
per second |
| 0 |
Calm
|
Sea like a mirror. |
0 |
0.0 |
<1 |
0.0-0.2 |
Calm |
Calm |
0.0 |
| 1 |
Light air |
Ripples with the appearance of scales
are formed, but without foam crests. |
2 |
0.8 |
1-3
|
0.3-1.5 |
Light |
Calm |
0.1 (0.1) |
| 2 |
Light breeze |
Small wavelets, still short
but more pronounced. Crests have a glassy appearance and
do not break. |
5 |
2.4 |
4-6 |
1.6-3.3 |
Light |
Smooth |
0.2 (0.3) |
| 3 |
Gentle breeze |
Large wavelets. Crests begin to break.
Foam of glassy appearance. Perhaps scattered white horses. |
9 |
4.3 |
7-10 |
3.4-5.4 |
Light |
Smooth |
0.6 (1.0) |
| 4 |
Moderate breeze |
Large waves begin to form; the
white foam crests are more extensive everywhere. Probably
some spray. |
13 |
6.7 |
11-16 |
5.5-7.9 |
Moderate |
Slight |
1.0 (1.5) |
| 5 |
Fresh breeze |
Moderate waves, taking a more pronounced
long form; many white horses are formed. Chance of some
spray |
19 |
9.3 |
17-21 |
8.0-10.7 |
Fresh |
Moderate |
2.0 (2.5) |
| 6 |
Strong breeze |
Large waves begin to form; the
white foam crests are more extensive everywhere. Probably
some spray. |
24 |
12.3 |
22-27 |
10.8-13.8 |
Strong |
Rough |
3.0 (4.0) |
| 7 |
Near gale |
Sea heaps up and white foam from breaking
waves begins to be blown in streaks along the direction
of the wind. |
30 |
15.5 |
28-33 |
13.9-17.1 |
Strong |
Very rough |
4.0 (5.5) |
| 8 |
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. |
37 |
18.9 |
34-40 |
17.2-20.7 |
Gale |
High |
5.5 (7.5) |
| 9 |
Strong gale |
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. |
44 |
22.6 |
41-47 |
20.8-24.4 |
Severe gale |
Very high |
7.0 (10.0) |
| 10 |
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 a white appearance.The
'tumbling' of the sea becomes heavy and shock-like. Visibility
affected. |
52 |
26.4 |
48-55 |
24.5-28.4 |
Storm |
Very high |
9.0 (12.5) |
| 11 |
Violent storm |
Exceptionally high waves (small and
medium-sized ships might be lost to view for a time 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. |
60 |
30.5 |
56-63 |
28.5-32.6 |
Violent storm |
Phenomenal |
11.5 (16.0) |
| 12 |
Hurricane |
The air is filled with foam
and spray. Sea completely white with driving spray; visibility
seriously affected. |
- |
- |
64 and over |
32.7 and over |
Hurricane force |
Phenomenal |
14.0 (-) |
* These columns are a guide to show roughly what may be
expected in the open sea, remote from land. Figures in
brackets indicate the probable maximum height of waves.
In enclosed waters, or when near land with an offshore
wind, wave heights will be smaller and the waves steeper. |
|
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