Force

Wind speed
(knots)

Wind description

Sea conditions

Probable Average Wave Height (Feet)*

0

0

Calm

Smooth, like a mirror

0

1

1-3

Light air

Small ripples like fish scales

¼-½

2

4-6

Light breeze

Short, small pronounced wavelets with no crests

¼-½

3

7-10

Gentle breeze

Large wavelets with some crests

2

4

11-16

Moderate breeze

Increasingly longer small waves, some with whitecaps (foam crests)

4

5

17-21

Fresh breeze

Moderate lengthening waves, with many whitecaps and some spray

6

6

22-27

Strong breeze

Large waves, extensive whitecaps, some spray

10

7

28-33

Near gale

Heaps of waves, with some breakers whose foam is blown downwind in streaks

14

8

34-40

Gale

Moderately high waves of increasing length and edges of crests breaking into spindrift (heavy spray); spray is blown downwind in well-marked streaks

18

9

41-47

Strong gale

High waves with dense foam streaks and some crests rolling over

23

10

48-55

Storm

Very high waves, with long overhanging crests; the sea looks white, visibility is greatly reduced, and waves tumble with force

29

11

56-63

Violent storm

Exceptionally high waves that may obscure medium-sized ships; all wave edges are blown into froth and the sea is covered with patches of foam

37

12

64-71

Hurricane

Air is filled with foam and spray, and sea is completely white

45