Beaufort

Beaufort wind force scale

"If Britannia rules the waves. And such, and a lot of nautical stuff derives from the Brits, how come wind speed is measured in Beaufort? That sounds awfully French."
-"Mr. Beaufort was Irish."
"HA"

History

The Beaufort wind force scale is a system to class the windspeed. Originally based on the behavour of an age-of-sail Frigate. Based on how many sails could be hoisted, how the ship behaved, and when sail had to be reduced. Created by Francis Beaufort in 1805. And with some alternation it was addobted by the Royal Navy in 1830.

Evolution

With the introduction of steamships, and the subsequent demise of sails. The system was altered and the wind forces were derived from the state of the sea in the open ocean.

Even more technological advancement meant wind speed could be measured physically. And wind speeds were assigned to the 13 force classes. And the speed measurements became the basis for the scale, making the Beaufort wind force scale technically a wind speed scale, although the name did not stay. The use of the name force has nothing to do with the Phycical unit Force. This conversion to speed was done both in km/h and knots. Rounding both to whole digits, the result is that if you where to converse one to the other the borders of the wind force classes don't match.

For sciency reasons, m/s is used nowadays too.

Weather forecasts

With the rise of meteorological record keeping, and producing weather forecasts. The Beaufort scale was extended with a description on how that wind acted on land.

Nowadays the Beaufort scale is still the main way wind speeds are reported, both in observations and in weather forecasts to both the general public on land, as to maritime news bulletins issued to ships.

Wind directions

Also from Beaufort

For log keeping and reporting weather, a letter code system has been created too. The use of this code reduces the space required in the logbook, and in messages.

Letter	Explenation
b	Blue sky
c	Detached clouds
d	Drizzling rain
f	Fog
g	Dark, gloomy
h	Hail
l	Lightning
m	Misty
o	overcast
p	Passing showers
q	Squally
r	Rain
s	Snow
t	Thunder
u	Ugly
v	Visibility
w	Wet, dew

The Beaufort wind force scale

With official descriptions.

Force	Description	Airspeed	Wave height	Sea conditions	Land conditions
0	Calm	< 1 knot < 1 km/h	0 m	Sea like a mirror.	Smoke rises vertically.
1	Light Air	1-3 knots 2-5 km/h	0-0.3 m	Ripples with the appearance of scales are formed, without foam crests.	Direction shown by smoke drift but not by wind vanes.
2	Light breeze	4-6 knots 6-11 km/h	0.3-0.6 m	Small wavelets still short but more pronounced. Crests have a glassy appearance but do not break.	Wind felt on face. Leaves rustle. Wind vane moved by wind.
3	Gentle Breeze	7-10 knots 12-19 km/h	0.6-1.2 m	Large wavelets. Crests are begin to break. Foam of glassy appearance. Perhaps scattered white horses.	Leaves and small twigs in constant motion. Light flags extended.
4	Moderate breeze	11-16 knots 20-28 km/h	1-2 m	Small waves becoming longer. Fairly frequent white horses	Raises dust and loose paper. Small branches moved.
5	Fresh breeze	17-21 knots 29-38 km/h	2-3 m	Moderate waves taking a more pronounced long form. Many white horses are formed. Chance of some spray	Small trees in leaf begin to sway. Crested wavelets form on inland waters.
6	Strong breeze	22-27 knots 39-49 km/h	3-4 m	Large waves begin to form. The white foam crests are more extensive everywhere. Probably some spray	Large branches in motion. Whistling heard in telegraph wires. Umbrellas used with difficulty.
7	High wind, Moderate gale, Near gale	28-33 knots 50-61 km/h	4-5.5 m	Sea heaps up and white foam from breaking waves begins to be blown in streaks along the direction of the wind. Spindrift begins to be seen.	Whole trees in motion. Inconvenience felt when walking against the wind.
8	Gale, Fresh gale	34-40 knots 62-74 km/h	5.5-7.5 m	Moderately high waves of greater length. Edges of crests break into spindrift. Foam is blown in well-marked streaks along the direction of the wind.	Twigs break off trees. Generally impedes progress.
9	Strong gale, Severe gale	41-47 knots 75-88 km/h	7-10 m	High waves. Dense streaks of foam along the direction of the wind. Sea begins to roll. Spray affects visibility.	Slight structural damage (chimney pots and slates removed).
10	Storm, Whole gale	48-55 knots 89-102 km/h	9-12.5 m	Very high waves with long overhanging crests. 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 on a white appearance. Rolling of the sea becomes heavy. Visibility affected	Seldom experienced inland. Trees uprooted. Considerable structural damage.
11	Violent storm	55-63 knots 103-117 km/h	11.5-16 m	Exceptionally high waves. Small- and medium-sized ships might be for a long time lost to view behind the waves. Sea is covered with long white patches of foam. Everywhere, the edges of the wave crests are blown into foam. Visibility affected.	Very rarely experienced. Accompanied by widespread damage.
12	Hurricane force	≥ 64 knots ≥ 118 km/h	≥ 14 m	The air is filled with foam and spray. Sea is completely white with driving spray. Visibility very seriously affected.	Devastation.

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