Scale |
Wind
Speed Kts/Mph |
Descriptive
term (WMO**) |
Conditions
Over land |
Conditions
Over sea |
wave
height (m) |
0 |
< 1Kts
< 1Mph |
Calm
|
Calm; smoke rises vertical.
|
Mirror like sea
|
0 |
1 |
1 - 3 Kts
1 - 3 Mph |
Light
air |
Direction of wind shown by smoke drift, but
not by wind vanes.
|
Ripples with the appearance
of scales are formed, but without foam crests. |
0.1 |
| 2 |
4 - 6 kts
5 - 7 Mph |
Light
Breeze |
Wind felt on face; leaves rustle; ordinary
vanes moved by wind.
|
Small wavelets, still short,
but more pronounced. Crests have a glassy appearance and do
not break. |
0.3 |
3 |
7 - 10 Kts
8 - 12 Mph |
Gentle
Breeze |
Leaves and small twigs in motion; wind extends
light flag.
|
Large wavelets. Crests
begin to break. Foam of glassy appearance. Perhaps scattered
white horses.
|
1 |
4 |
11 - 16 Kts
13 - 18 Mph
|
Moderate
Breeze |
Raises dust and loose paper; small branches
move.
|
Small waves, becoming larger;
fairly frequent white horses.
|
1.5 |
5 |
17 - 21 Kts
20 - 24 Mph |
Fresh
Breeze |
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.
|
2.5 |
6 |
22 - 27 Kts
25 - 31 Mph |
Strong
Breeze |
Large branches in motion; whistling heard
in telegraph wires.
|
Large waves begin to form;
the white foam crests are more extensive everywhere. Probably
some spray.
|
4 |
7 |
28 - 33 Kts
32 -38 Mph
|
Near
Gale |
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.
|
5.5 |
8 |
34 - 40 Kts
39 - 46 Mph |
Gale
|
Breaking twigs off trees; generally impedes
progress. |
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.
|
7.5 |
9 |
41 - 47 Kts
47 - 54 Mph |
Severe
Gale |
Slight structural damage occurs. |
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 |
10 |
48 - 55 Kts
55 -63 Mph |
Storm
|
Seldom experienced inland; trees uprooted;
considerable structural damage occurs.
|
Very high waves with long
over- hanging crests. The resulting foam 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 from the
foam. Visibility affected.
|
12.5 |
11 |
56 - 63 Kts
64 - 73 Mph |
Violent
Storm |
Very rarely experienced; accompanied by wide-spread
damage |
Exceptionally high waves.
The sea is completely covered with long white patches of foam
lying along the direction of the wind. The edges of the wave
crests are blown into froth. Visibility affected.
|
16 |
12 |
> 64 Kts
> 74 Mph |
Hurricane
|
Extensive damage |
The air is filled with
foam and spray. Sea surface white with driving spray; visibility
badly affected.
|
>16 |
The wind speeds refer to sustained wind speed
at 10m above the surface, not transient gusts which may be considerably
stronger. Sea states are a guide and should not be used to judge
wind speed.
