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. |