Effects on Land / Sea

m/s

knots

mph

km/h

0

0-0.2

0-1

0-1

0-1

Calm

Smoke rises vertically.
Sea is as calm as a mirror.

1

0.3-1.5

1-3

1-3

1-5

Light Air

Smoke drifts slowly.
Scaly ripples, no foam crests.

2

1.6-3.3

4-6

4-7

6-11

Light Breeze

Wind felt on face, leaves rustle.
Glassy crests, not breaking.

3

3.4-5.4

7-10

8-12

12-19

Gentle Breeze

Leaves and flags in motion.
Larger crests breaking, scattered whitecaps.

4

5.5-7.9

11-16

13-18

20-28

Moderate
Breeze

Small branches move, loose paper raised into the air.
Small waves growing longer, numerous whitecaps.

5

8.0-10.7

17-21

19-24

29-38

Fresh Breeze

Small trees sway.
Moderate waves in longer form, many white caps, some spray.

6

10.8-13.8

22-27

25-31

39-49

Strong Breeze

Large branches sway, whistling heard in power wires, umbrellas used with difficulty.
Larger waves, more spray, whitecaps seen everywhere.

7

13.9-17.1

28-33

32-38

50-61

Near Gale

Whole trees moving, resistance felt walking against the wind.
Heaps of waves, streaks of foam from breaking waves.

8

17.2-20.7

34-40

39-46

62-74

Gale

Twigs break off, walking against the wind impeded.
Fairly high waves of greater length, well-marked streaks.

9

20.8-24.4

41-47

47-54

75-88

Strong Gale

Large branches break off, slight structural damage.
High waves, rolling sea, dense streaks. Visibility reduces.

10

24.5-28.4

48-55

55-63

89-102

Storm

Trees uprooted, significant structural damage.
Sea is white in foam with very high waves colliding each other. Heavy rolling sea with further reduced visibility.

11

28.5-32.6

56-63

64-72

103-117

Violent Storm

Widespread damage.
Exceptionally high waves, sea covered with white foam. Violent rolling sea with significantly reduced visibility.

12

32.7-36.9

64-71

73-82

118-133

Hurricane

Violent movement of trees. Extreme damage. This is seldom encountered on land
Phenomenal waves, air filled with foam and driving spray. Visibility greatly reduced.。