Marine Radio
in Tasmania



Beaufort Wind Scale Force

The Beaufort Scale for determining wind speed derived from observations of the sea state have been a useful although not very accurate method of estimating wind speed by mariners.

The scale was created by the British Admiral Sir Francis Beaufort in 1806 who used the sea state for standising the description for wind speeds. Later Sir George Simpson, Director of the UK Meteorological Office from 1920 to 1938, modified the descriptions of the Beaufort scale wind speeds by providing land based observations, a much more accurate method of wind speed measurement. When at sea the mariner will be aware that the duration, direction, fetch and currents will have a significant influence on the build up of a sea yet the wind speed might have remained constant. Simpson is the great uncle of the author of this site.

 

Beaufort number Description Wind speed Wave height Sea conditions Land conditions
km/h mph ks m/s m ft
0 Calm < 1 < 1 < 1 < 0.3 0 0 Flat. Calm. Smoke rises vertically.
1 Light air 1.1 – 5.5 1 – 3 1 – 2 0.3 – 1.5 0 – 0.2 0 – 1 Ripples without crests. Wind motion visible in smoke.
2 Light breeze 5.6 –11 4 – 7 3 – 6 1.6 – 3.4 0.2 – 0.5 1 – 2 Small wavelets. Crests of glassy appearance, not breaking Wind felt on exposed skin. Leaves rustle.
3 Gentle breeze 12 – 19 8 – 12 7 – 10 3.4 – 5.4 0.5 – 1 2 – 3.5 Large wavelets. Crests begin to break; scattered whitecaps Leaves and smaller twigs in constant motion.
4 Moderate breeze 20 – 28 13 – 17 11 – 15 5.5 – 7.9 1 – 2 3.5 – 6 Small waves with breaking crests. Fairly frequent white horses. Dust and loose paper raised. Small branches begin to move.
5 Fresh breeze 29 – 38 18 – 24 16 – 20 8.0 – 10.7 2 – 3 6 – 9 Moderate waves of some length. Many white horses. Small amounts of spray. Branches of a moderate size move. Small trees begin to sway.
6 Strong breeze 39 – 49 25 – 30 21 – 26 10.8 – 13.8 3 – 4 9 – 13 Long waves begin to form. White foam crests are very frequent. 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 31 – 38 27 – 33 13.9 – 17.1 4 – 5.5 13 – 19 Sea heaps up. 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. Swaying of skyscrapers may be felt, especially by people on upper floors.
8 Gale, Fresh gale 62 – 74 39 – 46 34 – 40 17.2 – 20.7 5.5 – 7.5 18 – 25 Moderately high waves with breaking crests forming spindrift. Well-marked streaks of foam are blown along wind direction. Considerable airborne spray. Some twigs broken from trees. Cars veer on road. Progress on foot is seriously impeded.
9 Strong gale 75 – 88 47 – 54 41 – 47 20.8 – 24.4 7 – 10 23 – 32 High waves whose crests sometimes roll over. Dense foam is blown along wind direction. 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. Damage to circus tents and canopies.
10 Storm, Whole gale 89 – 102 55 – 63 48 – 55 24.5 – 28.4 9 – 12.5 29 – 41 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 64 – 72 56 – 63 28.5 – 32.6 11.5 – 16 37 – 52 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 ≥ 73 ≥ 64 ≥ 32.7 ≥ 14 ≥ 46 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.

Beaufort Scale courtesy of Wikipedia.

 
Updated 25 July 2017. © Copyright. A Douglas 2017