Beaufort Number
or Force

Wind Speed

Description

Effects on Land and Sea

MPH

Knots

0

<1

<1

Calm

Still, calm air, smoke will rise vertically

Water surface is mirror-like

1

1 to 3

1 to 3

Light Air

Rising smoke drifts, wind vane is inactive

Small ripples appear on water surface

2

4 to 7

4 to 6

Light Breeze

Leaves rustle, can feel wind on your face, wind vanes begin to move

Small wavelets develop, crests are glassy

3

8 to 12

7 to 10

Gentle Breeze

Leaves and small twigs move, light weight flags extend

Large wavelets, crests start to break, some whitecaps

4

13 to 18

11 to 16

Moderate Breeze

Small branches move, raises dust, leaves and paper

Small waves develop, becoming longer, whitecaps

5

19 to 24

17 to 21

Fresh Breeze

Small trees sway

White crested wavelets (whitecaps) form, some spray

6

25 to 31

22 to 27

Strong Breeze

Large tree branches move, telephone wires begin to whistle, umbrellas are difficult to keep under control

Larger waves form, whitecaps prevalent, spray

7

32 to 38

28 to 33

Moderate
or Near Gale

Large trees sway, becoming difficult to walk

Larger waves develop, white foam from breaking waves begins to be blown

8

39 to 46

34 to 40

Gale

Twigs and small branches are broken from trees, walking is difficult

Moderately large waves with blown foam

9

47 to 54

41 to 47

Strong Gale

Slight damage occurs to buildings, shingles are blown off of roofs

High waves (6 meters), rolling seas, dense foam. Blowing spray reduces visibility

10

55 to 63

48 to 55

Storm

Trees are broken or uprooted, building damage is considerable

Large waves (6-9 meters), overhanging crests, sea becomes white with foam, heavy rolling, reduced visibility

11

64 to 72

56 to 63

Violent Storm

Extensive and widespread damage

Large waves (9-14 meters), white foam, visibility further reduced

12

> 73

> 64

Hurricane

Extreme destruction and devastation

Large waves over 14 meters, air filled with foam, sea white with foam and driving spray, little visibility