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Beaufort Wind Force Scale

Rear-Admiral, Sir Francis Beaufort, was born in Ireland in 1774. He entered the Royal Navy at the age of 13 and was a midshipman aboard the Aquilon. By 1800 he had risen to the rank of Commander. In the summer of 1805 Beaufort was appointed to the command of the Woolwich, a 44 gun man-of-war.

In 1806 he wrote in his log book a wind force scale. The scale was simple and very simular to one that Alexander Dalrymple had written in a book in 1789. A year later he added some criteria to the 0-12 scale that indicated how much of a ship's sails would be employed by a British man-of-war under each condition. It was not relate to the speed of the wind.

Over the following years he continued to use his scale in his logs. It was finally adopted in December 1838 by the British Admiralty for use in all Royal Navy logbooks. However, as ship design and the introduction of steam power became widespread even that scale had to be modified.

In 1912 the International Commission for Weather Telegraphy sought some agreement on velocity equivalents for the Beaufort scale. A uniform set of equivalents was accepted in 1926 and revised slightly in 1946, extending the scale to 17 values (the added five values further refining the hurricane-force winds). By 1955, wind velocities in knots replaced Beaufort numbers on weather maps.

Today's Beaufort Scale including the observed land conditions...

Beaufort Wind Force	Wind				Criterion
	Speed		Descriptive term		Sea			Land
	Average	Range	American	British	State	Description	Wave Height	Land
0	0	<1 kt <1 mph <1 kph	Light	Calm	Calm	Sea like a mirror.	0	Smoke rises vertically.
1	2 kt 2 mph 3 kph	1-3 kts 1-3 mph 1-5 kph	Light	Light air	Smooth	Ripples with the appearance of scales are formed, but without foam crests.	¼ ft 0.1 m	Direction shown by smoke but not by wind vanes.
2	5 kts 6 mph 9 kph	4-6 kts 4-7 mph 6-11 kph	Light	Light breeze	Smooth	Small wavelets, still short but more pronounced, crests have a glassy appearance and do not break.	½-1 ft 0.2 m	Wind felt on face; leaves rustle; ordinary vane moved by wind.
3	9 kts 10 mph 16 kph	7-10 kts 8-12 mph 12-19 kph	Gentle	Gentle breeze	Slight	Large wavelets. Crests begin to break. Foam of glassy appearance.	2-3 ft 0.6 m	Leaves and small twigs in constant motion; wind extends light flag.
4	13 kts 16 mph 24 kph	11-16 kts 13-18 mph 20-28 kph	Moderate	Moderate breeze	Moderate	Small waves, becoming longer.	3½-5 ft 1 m	Raises dust and loose paper; small branches are moved.
5	19 kts 22 mph 34 kph	17-21 kts 19-24 mph 29-38 kph	Fresh	Fresh breeze	Rough	Moderate waves, taking a more pronounced long form. (Chance of some spray).	6-8 ft 2 m	Small trees in leaf begin to sway.
6	24 kts 28 mph 44 kph	22-27 kts 25-31 mph 39-49 kph	Strong	Strong breeze	Very Rough	Large waves begin to form; the white foam crests are more extensive everywhere. (Probably some spray).	9½-13 ft 3 m	Large branches in motion; umbrellas used with difficulty.
7	30 kts 35 mph 561 kph	28-33 kts 32-38 mph 50-61 kph	Strong	Near gale	High	Sea heaps up and white foam from breaking waves begins to be blown in streaks along the direction of the wind.	13½-19 ft 4 m	Whole trees in motion; inconvenience felt when walking against the wind.
8	37 kts 43 mph 68 kph	34-40 kts 39-46 mph 62-74 kph	Gale	Gale	Very High	Moderately high waves of greater length; edges of crests begin to break into spondrift. The foam is blown in well marked streaks along the direction of the wind.	18-28 ft 5.5 m	Breaks twigs off trees; generally impedes progress
9	44 kts 51 mph 82 kph	41-47 kts 47-54 mph 75-88 kph	Gale	Strong Gale	Very High	High waves. Dense streaks of foam along the direction of the wind. Crests of waves begin to topple, tumble and roll over. Spray may affect visibility.	23-32 ft 7 m	Slight structural damage; chimney-pots and slates removed.
10	52 kts 59 mph 96 kph	48-55 kts 55-63 mph 89-102 kph	Whole Gale	Storm	Phenomenal	Very high waves with long overhanging crests. The resulting foam in great patches is blown in dense white streaks along the direction of the wind. On the whole the surface of the sea takes a white appearance. Visibility affected.	29-41 ft 9 m	Trees uprooted; considerable structural damage.
11	60 kts 68 mph 110 kph	56-63 kts 64-72 mph 103-117 kph	Whole Gale	Violent Strom	Phenomenal	Exceptionally high waves. (Small and medium sized ships might be for a time lost to view behind the waves.) The sea is completely covered with long white patches of foam lying along the direction of the wind. Everywhere the edges of the wave crests are blown into froth. Visibility affected.	39-46 ft 11.5 m	Widespread damage; very rarely experienced.
12	68 kts 78 mph 124 kph	64-71 kts 72-82 mph 118-132 kph	Hurricane	n/a	n/a	The air is filled with foam and spray. Sea completely white with driving spray; visibility very seriously affected.	>52 ft >14 m	Countryside is devastated.
13	76 kts 88 mph 141 kph	72-80 kts 83-92 mph 133-148 kph
14	85 kts 98 mph 157 kph	81-89 kts 93-103 mph 149-165 kph
15	95 kts 109 mph 175 kph	90-99 kts 104-114 mph 166-183 kph
16	104 kts 120 mph 192 kph	100-108 kts 115-125 mph 184-200 kph
17		>108 kts >125 mph >200 kph
Beaufort Wind Force	Average	Range	American	British	State	Description	Wave Height	Land
	Speed		Descriptive term		Sea			Land
	Wind				Criterion

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National Weather Service Southern Region Headquarters 819 Taylor Street Fort Worth, Texas 76102	www.srh.weather.gov Updated: March 29, 2006

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