Beaufort Wind Scale

Developed in 1806 by Sir Francis Beaufort of England

The Beaufort Scale was created to standardize wind strength observations. Eventually adopted by the Royal Navy in 1830 it became the standard. With slight variations over the years, the scale is still used in some countries. Nowadays there are many more instruments and wind gauges available. However the Beaufort Scale is still the best way to estimate the wind speed based purely on visual observations of the sea state. In some countries, the scale goes beyond 12, and has classifications from 13-17, which are for special situations like typhoons (hurricanes). Here is the most common version of the Beaufort Scale.

Force	Wind (Knots)	Wind (mph)	WMO Classification	Appearance of Wind Effects
Force	Wind (Knots)	Wind (mph)	WMO Classification	On the Water	On Land
0	Less than 1	Less than 1	Calm	Sea surface smooth and mirror-like	Calm, smoke rises vertically
1	1-2	1-3	Light Air	Scaly ripples, no foam crests	Smoke drift indicates wind direction, still wind vanes
2	3-6	4-6	Light Breeze	Small wavelets, crests glassy, no breaking	Wind felt on face, leaves rustle, vanes begin to move
3	7-10	8-12	Gentle Breeze	Large wavelets, crests begin to break, scattered whitecaps	Leaves and small twigs constantly moving, light flags extended
4	11-15	13-17	Moderate Breeze	Small waves 1-4 ft. becoming longer, numerous whitecaps	Dust, leaves, and loose paper lifted, small tree branches move
5	16-20	18-24	Fresh Breeze	Moderate waves 4-8 ft taking longer form, many whitecaps, some spray	Small trees in leaf begin to sway
6	21-26	25-30	Strong Breeze	Larger waves 8-13 ft, whitecaps common, more spray	Larger tree branches moving, whistling in wires
7	27-33	31-38	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	39-46	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	47-54	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	55-63	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	64-72	Violent Storm	Exceptionally high (30-45 ft) waves, foam patches cover sea, visibility more reduced	Trees are broken off or uprooted, saplings bent and deformed. Poorly attached asphalt shingles and shingles in poor condition peel off roofs.
12	64+	73+	Hurricane	Air filled with foam, waves over 45 ft, sea completely white with driving spray, visibility greatly reduced	Very widespread damage to vegetation. Some windows may break; mobile homes and poorly constructed sheds and barns are damaged. Debris may be hurled about.

Local Effects on the Beaufort Scale: When using the Beaufort Scale, keep in mind that it was developed for seagoing vessels. The observations for wave size would apply to open water with a large enough fetch. Closer to shore or on enclosed waterways the observations could be quite different. Indeed the local topography and wind effects could greatly affect the actual wind speeds in a given area.

Knots: abbrev “kn” (sometimes “kt” or “kts”), are Nautical miles per hour. A nautical mile is approximately 1.151 standard miles.

Whitecaps: aka “White Horses” are breaking wave crests that can be observed in windy conditions. White caps begin to appear at 8-10 knots, and are more frequent in 15 knots.

Units of speed: abbrev “mph”, are a more common unit of speed in the US. In Europe kilometers “Kph” or “m/s” (meters per second) are sometimes used.

National Weather Service’s – Watch, Warning, & Advisory

Watch – A watch is used when the risk of a hazardous weather or hydrologic event has increased significantly, but its occurrence, location or timing is still uncertain. It is intended to provide enough lead time so those who need to set their plans in motion can do so. A watch means that hazardous weather is possible. People should have a plan of action in case a storm threatens and they should listen for later information and possible warnings especially when planning travel or outdoor activities.

Warning – A warning is issued when a hazardous weather or hydrologic event is occurring, imminent or likely. A warning means weather conditions pose a threat to life or property. People in the path of the storm need to take protective action.

Advisory – An advisory is issued when a hazardous weather or hydrologic event is occurring, imminent or likely. Advisories are for less serious conditions than warnings, that cause significant inconvenience and if caution is not exercised, could lead to situations that may threaten life or property.

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