The Beaufort Scale
The scale was created in 1805 by Sir Francis Beaufort, an Irish-born British admiral and hydrographer. The scale that carries Beaufort's name had a long and complex evolution, from the previous work of others, to when Beaufort was a top administrator in the Royal Navy in the 1830s. 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 getting things standardized.
The initial scale of thirteen classes (zero to twelve) did not reference wind speed numbers but related qualitative wind conditions to effects on the sails of a man of war, then the main ship of the Royal Navy, from "just sufficient to give steerage" to "that which no canvas sails could withstand." At zero, all his sails would be up; at six, half of his sails would have been taken down; and at twelve, all sails would be stowed away.
The scale was made a standard for ship's log entries on Royal Navy vessels in the late 1830s and was adapted to non-naval use from the 1850s, with scale numbers corresponding to cup anemometer rotations. In 1906, to accommodate the growth of steam power, the descriptions were changed to how the sea, not the sails, behaved and extended to land observations. Rotations to scale numbers were standardized only in 1923. George Simpson, Director of the UK Meteorological Office, was responsible for this and for the addition of the land-based descriptors. The measure was slightly altered some decades later to improve its utility for meteorologists. Today, many countries have abandoned the scale and use the SI-based units m/s or km/h instead,[citation needed] but the severe weather warnings given to public are still approximately the same as when using the Beaufort scale.
The Beaufort scale was extended in 1946, when Forces 13 to 17 were added. However, Forces 13 to 17 were intended to apply only to special cases, such as tropical cyclones. Nowadays, the extended scale is only used in Taiwan and mainland China, which are often affected by typhoons.
Wind speed on the 1946 Beaufort scale is based on the empirical formula: v = 0.836 B3/2 m/sw here v is the equivalent wind speed at 10 meters above the sea surface and B is Beaufort scale number. For example, B = 9.5 is related to 24.5 m/s which is equal to the lower limit of "10 Beaufort". Using this formula the highest winds in hurricanes would be 23 in the scale.
Today, hurricane force winds are sometimes described as Beaufort scale 12 through 16, very roughly related to the respective category speeds of the Saffir-Simpson Hurricane Scale, by which actual hurricanes are measured, where Category 1 is equivalent to Beaufort 12. However, the extended Beaufort numbers above 13 do not match the Saffir-Simpson Scale. Category 1 tornadoes on the Fujita and TORRO scales also begin roughly at the end of level 12 of the Beaufort scale but are indeed independent scales.
Note that wave heights in the scale are for conditions in the open ocean, not along the shore.
The Modern Scale
0 Description Wind speed Wave height Sea conditions Land conditions
km/h mph kts m/s m ft
Calm < 1 < 1 < 1 <0.3 0 0 Flat. Calm.Smoke rises
vertically.
1 Description Wind speed Wave height Sea conditions Land conditions km/h mph kts m/s m ft
Light air 1–5 1–3 1–2 0.3–1.5 0–0.2 0–1 Ripples without Wind motion crests. visible in smoke.
2 Description Wind speed Wave height Sea conditions Land conditions km/h mph kts m/s m ft
Light breeze 6–11 3 7 3-6 1.5–3.3 0.2–0.5 1–2 Small wavelets. Wind felt on
Crests of glassy exposed skin.
appearance, not Leaves rustle.
breaking
3 Description Wind speed Wave height Sea conditions Land conditions km/h mph kts m/s m ft Gentle breeze 12–19 8–12 7–10 3.3–5.5 0.5–1 2–3.5 Large wavelets. Leaves and
Crests begin to smaller twigs
break; scattered in constant
whitecaps motion.
4 Description Wind speed Wave height Sea conditions Land conditions km/h mph kts m/s m ft Moderate breeze 20–28 13–17 11–15 5.5–8.0 1–2 3.5–6 Small waves with Dust and loose
breaking crests. paper raised.
Fairly frequent Small branches
white horses. begin to move.
5 Description Wind speed Wave height Sea conditions Land conditions km/h mph kts m/s m ft
Fresh breeze 29–38 18–24 16–20 8.0–11 2–3 6–9 Moderate waves of Branches of a
some length.Many moderate size
white horses.Small size move.
amounts of spray. Small trees begin to sway.
6 Description Wind speed Wave height Sea conditions Land conditions km/h mph kts m/s m ft
Strong breeze 39–49 25–30 21–26 11–14 3–4 9–13 Long waves begin to Large branches
form. White foam in motion.
crests are very Whistling heard frequent.Some in overhead
airborne spray wires.Umbrella is present. use becomes
difficult. Empty plastic garbage
cans tip over.
7 Description Wind speed Wave height Sea conditions Land conditions km/h mph kts m/s m ft
High wind,
Moderate gale,
Near gale 50–61 31–38 27–33 14–17 4–5.5 13–19 Sea heaps up. Some Whole trees in motion.
foam from breaking waves Effort to walk against the is blown into streaks along Swaying of skyscrapers
wind direction. Moderate may be felt, by people amounts of airborne spray. on upper floors.
8 Description Wind speed Wave height Sea conditions Land conditions km/h mph kts m/s m ft
Gale, Fresh gale 62-74 39–46 34–40 17–20 5.5–7.5 18–25 Moderately high waves Some twigs broken forming spindrift. from trees. Cars veer Well-marked streaks of on road. Progress on foam are blown along foot is seriously impeded. wind direction. Considerable airborne spray.
9 Description Wind speed Wave height Sea conditions Land conditions
km/h mph kts m/s m ft Strong gale 75–88 47–54 41–47 21–24 7–10 23–32 High waves whose crests Some branches break off
sometimes roll over. Dense trees, some small trees
foam is blown along wind blow over. direction. Large amounts of Construction/temporary airborne spray may begin to signs and blow over.
reduce visibility. Damage circus tents and canopies.
10 Description Wind speed Wave height Sea conditions Land conditions km/h mph kts m/s m ft
Storm Whole gale 89–102 55–63 48–55 25–28 9–12.5 29–41 Very high waves Trees are broken off with overhanging or uprooted,
crests.Large patches saplings bent and of foam from deformed.
wave crests give the Poorly attached Roof sea a white tiles asphalt
appearance. shingles and shingles Considerable tumbling in poor condition of waves with heavy peel off roofs.
amounts of airborne
spray reduce
visibility.
11 Description Wind speed Wave height Sea conditions Land conditions km/h mph kts m/s m ft
Violent storm 103–117 64–72 56–63 29–32 11.5–16 37–52 Exceptionally high Widespread vegetation waves. Very damage. Many roofing large patches of surfaces are damaged;
foam, driven before Roof tiles,asphalt tiles the wind,cover much that have curled up of the sea surface. and/or fractured due
Very large of airborne to age may break spray. Severely away reduce visibility.
12 Description Wind speed Wave height Sea conditions Land conditions km/h mph kts m/s m ft
Tropical Cyclone
Hurricane ≥ 118 ≥ 73 ≥ 64 ≥ 33 ≥ 14 ≥ 46 Huge waves. Sea is Very widespread damage completely white to vegetation. Some with and spray. Air windows may break; is filled with driving Caravans/mobile homes spray, greatly and poorly constructed
reducing visibility. sheds and barns are damaged. Debris may be hurled about.
12-17
Description Wind speed Wave height Sea conditions Land conditions km/h mph kts m/s m ft
12 Tropical Cyclone 118-133 73-82 64-71 33.7-36.9 ≥ 14 ≥ 46 Huge waves. Sea is Very rarely Experreced on 13 Hurricane 134-149 83-92 72-80 37.0-41.4 " " completelywhite with land; Usually accompanied
14 150-166 93-103 81-89 41.5-46.1 " " foam and spray. Air is by wide spread damage or
15 167-183 104-114 90-99 46.2-50.9 " " filled with driving total destruction. There
16 184-201 115-125 100-108 51.0-56.0 " " spray,greatly reducing may loss of life.
17 202-230 126-136 109-118 56.1-61.2 " " visibility.
