Beaufort
number
(force) |
Wind Speed |
Description |
Effects observed on the sea |
| knots |
mph |
| 0 |
under 1 |
under 1 |
Calm |
Sea is like a mirror |
| 1 |
1 - 3 |
1 - 3 |
Light air |
Ripples with appearance of scales; no foam crests |
| 2 |
4 - 6 |
4 - 7 |
Light breeze |
Small wavelets; crests of glassy appearance, not breaking |
| 3 |
7 - 10 |
8 - 12 |
Gentle breeze |
Large wavelets; crests begin to break; scattered whitecaps |
| 4 |
11-16 |
13-18 |
Moderate breeze |
Small waves, becoming longer; numerous whitecaps |
| 5 |
17-21 |
19-24 |
Fresh breeze |
Moderate waves, taking longer form; many whitecaps; some spray |
| 6 |
22-27 |
25-31 |
Strong breeze |
Larger waves forming; whitecaps everywhere; more spray |
| 7 |
28-33 |
32-38 |
Near gale |
Sea heaps up; white foam from breaking waves begins to be blown in
streaks |
| 8 |
34-40 |
39-46 |
Gale |
Moderately high waves of greater length; edges of crests begin to
break into spindrift; foam is blown in well-marked streaks |
| 9 |
41-47 |
47-54 |
Strong gale |
High waves; sea begins to roll; dense streaks of foam; spray may begin
to reduce visibility |
| 10 |
48-55 |
55-63 |
Storm |
Very high waves with overhanging crests; sea takes white appearance as
foam is blown in very dense streaks; rolling is heavy and visibility is
reduced |
| 11 |
56-63 |
64-72 |
Violent storm |
Exceptionally high waves; sea covered with white foam patches;
visibility further reduced |
| 12 |
64 and over |
73 and over |
Hurricane |
Air filled with foam; sea completely white with driving spray;
visibility greatly reduced |