Wind: know how strong it is with your eyes

The Beaufort Wind Force Scale is the best way of assessing the wind speed of a determined spot, with your eyes only. By observing the ocean and land, it is possible to measure the average wind force.

Although it is not a 100% accurate tool - the best anemometers in the world do it perfectly - the Beaufort Wind Force Scale lets you know if windsurfing is possible, or not.

The scale goes from "Calm", the level 0, to "Hurricane Force", the 12th level. The last stage of the Beaufort Wind Force Scale indicates you're experiencing more than 64 knots of winds. The 6th level on, there are associated warning flags and you won't probably be windsurfing from the 10th level, in which storm warnings are raised.

The Beaufort Wind Force Scale is very important for amateur windsurfers, but should also be taken into consideration by all experienced sailors. If you're riding in extreme wind conditions, the probabilities of damaging your sail are very high.

Sir Francis Beaufort, an Irish-born Royal Navy Officer, created the Beaufort Wind Force Scale, in 1805. He developed a wind speed empirical model that could be understood by everyone. It includes a level, a general weather description, the wind speed, the wave height, sea and land conditions, a sea state photo and the associated warning flag.

Here's the Beaufort Wind Force Scale:

BEAUFORT SCALE

WIND SPEED (km/h)

DESCRIPTION

WAVE HEIGHT (mt)

SEA CONDITIONS

LAND CONDITION

0

<1

Calm

0

Flat.

Calm. Smoke rises vertically.

1

1-5

Light air

0.1

Ripples without crests.

Wind motion visible in smoke.

2

6-11

Light breeze

0.2

Small wavelets. Crests of glassy appearance, not breaking.

Wind felt on exposed skin. Leaves rustle.

3

12-19

Gentle breeze

0.6

Large wavelets. Crests begin to break; scattered whitecaps.

Leaves and smaller twigs in constant motion.

4

20-28

Moderate breeze

1

Small waves.

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

5

29-38

Fresh breeze

2

Moderate (1.2 m) longer waves. Some foam and spray.

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

6

39-49

Strong breeze

3

Large waves with foam crests and some spray.

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

7

50-61

High wind, Moderate Gale, Near Gale

4

Sea heaps up and foam begins to be blown in streaks in wind direction.

Whole trees in motion. Effort needed to walk against the wind. Swaying of skyscrapers may be felt, especially by people on upper floors.

8

62-74

Fresh Gale

5.5

Moderately high waves with breaking crests forming spindrift. Streaks of foam.

Twigs broken from trees. Cars veer on road.

9

75-88

Strong Gale

7

High waves (6-7 m) with dense foam. Wave crests start to roll over. Considerable spray.

Larger branches break off trees, and some small trees blow over. Construction/temporary signs and barricades blow over. Damage to circus tents and canopies.

10

89-102

Whole Gale/Storm

9

Very high waves. 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

103-117

Violent storm

11.5

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 vegetation damage. More damage to most roofing surfaces, asphalt tiles that have curled up and/or fractured due to age may break away completely.

12

≥118

Hurricane-force

≥14

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

Considerable and widespread damage to vegetation, a few windows broken, structural damage to mobile homes and poorly constructed sheds and barns. Debris may be hurled about.