Beaufort number

Description

Wind speed (km/h)

Wave height (metres)

Sea conditions

Land conditions

0

Calm

<1

0

Flat

Calm. Smoke rises vertically.

1

Light air

1.1-5.5

0-0.2

Ripples without crests.

Smoke drift indicates wind direction and wind vanes cease moving.

2

Light breeze

5.6-11

0.2-0.5

Small wavelets.

Wind felt on exposed skin. Leaves rustle and wind vanes begin to move.

3

Gentle breeze

12-19

0.5-1

Large wavelets.

Leaves and small twigs constantly moving, light flags extended.

4

Moderate breeze

20-28

1-2

Small waves with breaking crests.

Dust and loose paper raised. Small branches begin to move.

5

Fresh breeze

29-38

2-3

Moderate waves of some length. Many whitecaps. Small amounts of spray.

Branches of a moderate size move. Small trees in leaf begin to sway.

6

Strong breeze

39-49

3-4

Long waves begin to form. Some airborne spray is present

Large branches in motion. Whistling heard in overhead wires. Umbrella use becomes difficult. Empty plastic garbage cans tip over.

7

High wind, moderate gale, near gale

50-61

4-5.5

Some foam from breaking waves is blown into streaks along wind direction. Moderate amounts of airborne spray.

Whole trees in motion. Effort needed to walk against the wind.

8

Gale, fresh gale

62-74

5.5-7.5

Moderately high waves with breaking crests forming spindrift. Considerable airborne spray.

Some twigs broken from trees. Cars veer on road. Progress on foot is seriously impeded.

9

Strong gale

75-88

7-10

High waves whose crests sometimes roll over. Large amounts of airborne spray may begin to reduce visibility.

Some branches break off trees, and some small trees blow over. Construction/temporary signs and barricades blow over.

10

Storm, whole gale, severe gale

89-102

9-12.5

Very high waves with overhanging crests. Large patches of foam from wave crests give the sea a white appearance. Considerable tumbling of waves with heavy impact. Large amounts of airborne spray reduce visibility

Trees are broken off or uprooted, saplings bent and deformed. Poorly attached asphalt shingles and shingles in poor condition peel off roofs.

11

Violent storm

103-117

11.5-16

Exceptionally high waves. Very large patches of foam, driven before the wind, cover much of the sea surface. Very large amounts of airborne spray severely reduce visibility

Widespread damage to vegetation. Many roofing surfaces are damaged; asphalt tiles that have curled up and/or fractured due to age may break away completely.

12

Hurricane force

>118

>14

Huge waves. Sea is completely white with foam and spray. Air is filled with driving spray, greatly reducing visibility

Very widespread damage to vegetation. Some windows may break; mobile homes and poorly constructed sheds and barns are damaged. Debris may be hurled about.