B |
Description |
Wind speed |
Wave height |
Sea conditions |
Land conditions |
Sea state photo |
Associated warning flag |
0 |
Calm |
< 1 knot |
0 ft |
Sea like a mirror |
Smoke rises vertically. |
|
|
< 1 mph |
< 2 km/h |
0 m |
< 0.5 m/s |
1 |
Light air |
1–3 knots |
0–1 ft |
Ripples with appearance of scales are formed, without foam crests |
Direction shown by smoke drift but not by wind vanes. |
|
|
1–3 mph |
2–5 km/h |
0–0.3 m |
0.5–1.5 m/s |
2 |
Light breeze |
4–6 knots |
1–2 ft |
Small wavelets still short but more pronounced; crests have a glassy appearance but do not break |
Wind felt on face; leaves rustle; wind vane moved by wind. |
|
|
4–7 mph |
6–11 km/h |
0.3–0.6 m |
1.6–3.3 m/s |
3 |
Gentle breeze |
7–10 knots |
2–4 ft |
Large wavelets; crests begin to break; foam of glassy appearance; perhaps scattered white horses |
Leaves and small twigs in constant motion; light flags extended. |
|
|
8–12 mph |
12–19 km/h |
0.6–1.2 m |
3.4–5.5 m/s |
4 |
Moderate breeze |
11–16 knots |
3.5–6 ft |
Small waves becoming longer; fairly frequent white horses |
Raises dust and loose paper; small branches moved. |
|
|
13–18 mph |
20–28 km/h |
1–2 m |
5.5–7.9 m/s |
5 |
Fresh breeze |
17–21 knots |
6–10 ft |
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. |
|
|
19–24 mph |
29–38 km/h |
2–3 m |
8–10.7 m/s |
6 |
Strong breeze |
22–27 knots |
9–13 ft |
Large waves begin to form; the white foam crests are more extensive everywhere; probably some spray |
Large branches in motion; whistling heard in telegraph wires; umbrellas used with difficulty. |
|
|
25–31 mph |
39–49 km/h |
3–4 m |
10.8–13.8 m/s |
7 |
High wind,
moderate gale,
near gale |
28–33 knots |
13–19 ft |
Sea heaps up and white foam from breaking waves begins to be blown in streaks along the direction of the wind; spindrift begins to be seen |
Whole trees in motion; inconvenience felt when walking against the wind. |
|
|
32–38 mph |
50–61 km/h |
4–5.5 m |
13.9–17.1 m/s |
8 |
Gale,
fresh gale |
34–40 knots |
18–25 ft |
Moderately high waves of greater length; edges of crests break into spindrift; foam is blown in well-marked streaks along the direction of the wind |
Twigs break off trees; generally impedes progress. |
|
|
39–46 mph |
62–74 km/h |
5.5–7.5 m |
17.2–20.7 m/s |
9 |
Strong / severe gale |
41–47 knots |
23–32 ft |
High waves; dense streaks of foam along the direction of the wind; sea begins to roll; spray affects visibility |
Slight structural damage (chimney pots and slates removed). |
|
|
47–54 mph |
75–88 km/h |
7–10 m |
20.8–24.4 m/s |
10 |
Storm,
whole gale |
48–55 knots |
29–41 ft |
Very high waves with long overhanging crests; 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; rolling of the sea becomes heavy; visibility affected |
Seldom experienced inland; trees uprooted; considerable structural damage. |
|
|
55–63 mph |
89–102 km/h |
9–12.5 m |
24.5–28.4 m/s |
11 |
Violent storm |
56–63 knots |
37–52 ft |
Exceptionally high waves; small- and medium-sized ships might be for a long time lost to view behind the waves; sea is covered with long white patches of foam; everywhere the edges of the wave crests are blown into foam; visibility affected |
Very rarely experienced; accompanied by widespread damage. |
|
|
64–72 mph |
103–117 km/h |
11.5–16 m |
28.5–32.6 m/s |
12 |
Hurricane force [7] |
≥ 64 knots |
≥ 46 ft |
The air is filled with foam and spray; sea is completely white with driving spray; visibility very seriously affected |
Devastation. |
|
|
≥ 73 mph |
≥ 118 km/h |
≥ 14 m |
≥ 32.7 m/s |
References: Met Office,[8] Royal Meteorological Society,[9] Encyclopædia Britannica[10] |