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Beaufort wind scale

The Beaufort scale is a system for measuring wind speed based on visual observations, and is still widely used despite the advent of modern wind gauges and other instruments. What is truly interesting is that this wind scale system is still referred to at all, considering it was developed in the early 1800’s! Our digital weather station and wind gauge on the island still read in the Beaufort scale as an option.

The scale was devised in 1805 by Sir Francis Beaufort, an Irish-born Royal Navy Officer. The scale that carries Beaufort’s name had a long and complex evolution, from the previous work of others. It was adopted officially and first used during Darwin’s voyage on HMS Beagle.

Some sort of scale was badly needed, as naval officers made regular weather observations, but there was no standard scale so observations were subjective – one man’s “stiff breeze” might be another’s “soft breeze”. Beaufort succeeded in standardizing the scale.

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. In 1916, to accommodate the growth of steam power, the descriptions were changed to how the sea, not the sails, behaved and extended to land observations. Today, many countries have abandoned the scale and use mph or kmph measurements, but the severe weather warnings given to public are still approximately the same as when using the Beaufort scale.

Many people, including our staff on the island, use visual references to estimate wind speeds, so although the Beaufort scale itself is becoming less used, its basic principle still lives on.

Beaufort #

Description

Wind mph

Wave height – feet

Sea conditions

Sea State Photo

Force 0

Calm

<1

0

Flat. “Seas like a mirror.”

Sea state Beaufort-force-0

Force 1

Light air

1-3

.25

Ripples with the appearance of scales but without foam crests.

Sea-state-beaufort-force-1

Force 2

Light breeze

4-7

.5-1

Small wavelets. Crests have a glassy appearance and do not break.

beaufort-force-2

Force 3

Gentle breeze

8-12

2-3

Large wavelets. Crests begin to break; scattered whitecaps.

beaufort-force-3

Force 4

Moderate breeze

13-17

3.5-5

Small waves with breaking crests. Fairly frequent whitecaps.

beaufort-force-4

Force 5

Fresh breeze

18-24

6-8

Moderate waves of some length. many whitecaps. Small amounts of spray.

beaufort-force-5

Force 6

Strong breeze

25-30

9-13

Long waves begin to form. White foam crests are very frequent. Some airborne spray is present.

beaufort-force-6

Force 7

High wind, moderate gale, near gale

31-38

13-19

Sea heaps up. White foam from breaking waves is blown into streaks along wind direction.

beaufort-force-7

Force 8

Gale

39-46

18-25

Moderately high waves with breaking crests forming spindrift. Well-marked streaks of foam are blown along wind direction. Considerable airborne spray.

beaufort-force-8

Force 9

Strong gale

47-54

23-32

High waves whose crests sometimes roll over. Dense foam is blown along wind direction. Large amounts of airborne spray may begin to reduce visibility.

beaufort-force-9

Force 10

Storm

55-63

29-41

Very high waves with overhanging crests. Large patches of foam from wave crests give the sea a white appearance. Considerable tumbling of waves with heavy impact. Large amounts of airborne spray reduce visibility.

beaufort-force-10

Force 11

Violent storm

64-72

36-52

Exceptionally high waves, small to medium sized ships may be lost to view behind the waves. Sea completely covered with long white patches of foam lying along wind direction. Everywhere the edges of wave crests are blown into froth.

beaufort-force-11

Force 12

Hurricane force

>73

>46

Huge waves. Sea is completely white with foam and spray. Air is filled with driving spray, greatly reducing visibility.

beaufort-force-12

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