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Boca Marina Yacht Club - Boating Resources - Beaufort Wind Scale

Home Boating & Weather Beaufort Wind Scale

The Beaufort Wind Scale is a scale that is used by seamen and coastal observers to estimate wind speed. The scale was created by British Rear Admiral Sir Francis Beaufort in the year 1805, and it was derived from his observations of sea conditions. It was especially important during the 19th century, because no sophisticated wind speed-measuring equipment was available at that time. Despite the introduction of new technologies, it is still being used by seafarers today, and it also applied to measure wind speed on land.

Force Wind
(Knots)
WMO
Classification
Appearance of Wind Effects
On the Water On Land
0 < 1 Calm Sea surface smooth and mirror-like Calm, smoke rises vertically
1 1-3 Light Air Scaly ripples, no foam crests Smoke drift indicates wind direction, still wind vanes
2 4-6 Light Breeze Small wavelets, crests glassy, no breaking Wind felt on face, leaves rustle, vanes begin to move
3 7-10 Gentle Breeze Large wavelets, crests begin to break, scattered whitecaps Leaves and small twigs constantly moving, light flags extended
4 11-16 Moderate Breeze Small waves 1-4 ft. becoming longer, numerous whitecaps Dust, leaves, and loose paper lifted, small tree branches move
5 17-21 Fresh Breeze Moderate waves 4-8 ft taking longer form, many whitecaps, some spray Small trees in leaf begin to sway
6 22-27 Strong Breeze Larger waves 8-13 ft, whitecaps common, more spray Larger tree branches moving, whistling in wires
7 28-33 Near Gale Sea heaps up, waves 13-20 ft, white foam streaks off breakers Whole trees moving, resistance felt walking against wind
8 34-40 Gale Moderately high (13-20 ft) waves of greater length, edges of crests begin to break into spindrift, foam blown in streaks Whole trees in motion, resistance felt walking against wind
9 41-47 Strong Gale High waves (20 ft), sea begins to roll, dense streaks of foam, spray may reduce visibility Slight structural damage occurs, slate blows off roofs
10 48-55 Storm Very high waves (20-30 ft) with overhanging crests, sea white with densely blown foam, heavy rolling, lowered visibility Seldom experienced on land, trees broken or uprooted, "considerable structural damage"
11 56-63 Violent Storm Exceptionally high (30-45 ft) waves, foam patches cover sea, visibility more reduced  
12 64 + Hurricane Air filled with foam, waves over 45 ft, sea completely white with driving spray, visibility greatly reduced  

 

History of the Beaufort Scale

 
 
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