Beaufort Wind Scale

June 6 2017.  In view of last night’s un-seasonal gale, I have here set-out the Beaufort Scale, the universally accepted scale for wind speed.  Nowadays – even in tv/radio weather forecasts, the term ‘gale’ or ‘storm’ is often misused, so here’s the correct calibration!

Wind Force Description Speed Specifications
km/h mph knots
0 Calm <1 <1 <1 Smoke rises vertically
1 Light Air 1-5 1-3 1-3 Direction shown by smoke drift but not by wind vanes
2 Light Breeze 6-11 4-7 4-6 Wind felt on face; leaves rustle; wind vane moved by wind
3 Gentle Breeze 12-19 8-12 7-10 Leaves and small twigs in constant motion; light flags extended
4 Moderate Breeze 20-28 13-18 11-16 Raises dust and loose paper; small branches moved.
5 Fresh Breeze 29-38 19-24 17-21 Small trees in leaf begin to sway; crested wavelets form on inland waters.
6 Strong Breeze 38-49 25-31 22-27 Large branches in motion; whistling heard in telegraph wires; umbrellas used with difficulty.
7 Near Gale 50-61 32-38 28-33 Whole trees in motion; inconvenience felt when walking against the wind.
8 Gale 62-74 39-46 34-40 Twigs break off trees; generally impedes progress.
9 Strong Gale 75-88 47-54 41-47 Slight structural damage (chimney pots and slates removed).
10 Storm 89-102 55-63 48-55 Seldom experienced inland; trees uprooted; considerable structural damage
11 Violent Storm 103-117 64-72 56-63 Very rarely experienced; accompanied by widespread damage.
12 Hurricane 118 plus 73 plus 64 plus Devastation

 

The scale was devised in 1805 by Irish-born Francis Beaufort (later Rear Admiral Sir Francis Beaufort), a Royal Navy officer, while serving on HMS Woolwich. The scale that carries Beaufort’s name had a long and complex evolution from the previous work of others (including Daniel Defoe the century before) to when Beaufort was Hydrographer of the Navy in the 1830s when it was adopted officially and first used during the voyage of HMS Beagle under Captain Robert FitzRoy, later to set up the first Meteorological Office (Met Office) in Britain giving regular weather forecasts.[1] In the early 19th century, naval officers made regular weather observations, but there was no standard scale and so they could be very subjective – one man’s “stiff breeze” might be another’s “soft breeze”. Beaufort succeeded in standardizing the scale.