Description

Beaufort Scale

Average Wind Speed (Knots)

Average Wind Speed (Mps)

Effects at Sea

Average Wave Height (m)

Highest Wave Height (m)

Calm

0

<1

<0.5

Sea like a mirror

-

-

Light air

1

1-3

0.5-1.5

Ripples, but no foam crests

0.1

0.1

Light breeze

2

4-6

2-3

Small wavelets

0.2

0.3

Gentle breeze

3

7-10

3.5-5

Large wavelets crests, not breaking

0.6

1

Moderate wind

4

11-16

5.5-8

Numerous whitecaps

1

1.5

Fresh wind

5

17-21

8.5-11

Many whitecaps, some spray

2

2.5

Strong wind

6

22-27

11.5-14

Larger waves form. Whitecaps everywhere. More spray

3

4

Very strong wind

7

28-33

14.5-17

White foam from breaking waves beings to be blown in streaks

4

5.5

Gale

8

34-40

17.5-20.5

Edges of wave crests begin to break into spindrift

5.5

7.5

Severe gale

9

41-47

21-24

High waves. Sea begins to roll. Spray may reduce visibility

7

10

Storm

10

48-55

24.5-28.5

Very high waves with overhanging crests. Blowing foam gives sea a white appearance

9

12.5

Severe storm

11

56-63

29-32.5

Exceptionally high waves

11.5

16

Hurricane force

12

>=64

>=33

Air filled with foam. Sea completely white. Visibility greatly reduced

>=14

-