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Beaufort Wind Scale

Beaufort scale, also known as Beaufort wind force scale, was discovered in 1805 by Commander (later Admiral and Knight Commander of the Bath) Francis Beaufort of the British navy for classifying and observing the wind force at sea. The Beaufort scale is used to measure and detail the consequences of different wind speeds on objects on land or at sea. 


The Beaufort numbers in the Beaufort scale are arranged from 0 to 12 to represent the wind strength from calm (force 0) to the hurricane ( force 12). The Beaufort scale was further extended in 1946 when forces 13 to 17 were added. The force 13 to 17 are applied only to special cases such as tropical cyclones. The extended scale is only used in Taiwan and Mainland China, which are often affected by typhoons. 


What is Beaufort Scale?

The Beaufort scale is used to measure the speed of the wind. It is based on observations rather than actual measurements. It is widely used to measure wind speed today. There are 12 levels, including 0 for “ no wind”  in the wind force scale introduced by Beaufort. The level in the Beaufort scale was further extended from 13 to 17 in 1946. All of them were labeled as hurricanes. The further ranges of scale were only used in special cases by China and Taiwan still because they often have typhoons.


Beaufort Scale Definition

Beaufort scale, a wind force scale ranging from 0 ( calm ) to 12 ( hurricane) is an empirical measure for describing the wind speed based on the observed sea conditions.


Wind Scale Beaufort

The wind scale by Beaufort is neither exact nor objective, rather it was based on the visual and subjective observation of a ship and of the sea. The corresponding wind speeds are identified later, but the values in different units were never made equal.


The Beaufort wind force scale is widely used in countries like  Hong Kong, Netherlands, Greece, China, Taiwan, Germany, Malta, and Macau, although with some differences between them. Taiwan uses the wind scale with the extension to 17. On 15 May 2006, China started using this extended version of scale without prior notice, and the extended version of the scale was instantly put to use for Typhoon Chanchu. However,  Hong Kong and Macau use force 12 as the maximum. 


The Beaufort Wind Force Scale Table

Beaufort Number

Description

Wind Speed

Sea Condition

Land Condition



knot

mph

km/h

m/s



0

Calm

< 1

< 1

< 2

< 0.5

Seal like a mirror

Smoke rises vertically

1

Light Air

1-3

1- 3

2 - 5

0.5 -1.5

Scaley ripples without foam crests

Direction indicated by smoke drift but not by wind vanes.

2

Light Breeze

4 - 6

4 - 7

6 -11

1.6 -3.3

Small wavelets,Glassy crest but do not break

Wind felt on race, leave rustles, wind vane moved by wind

3

Gentle Breeze

7 - 10

8 - 12

12 -19

3.4 - 5.5

Large wavelets, crest begin to break, form of glassy appearances possibly scattered whitehorse

Leaves and small twigs in constant motion, light flags extended

4

Moderate Breeze

11 -16

13 - 18

20 - 28

5.5 - 7.9

Small waves becoming wider, frequent white horses

Raise dust and loose paper, small branches moved

5

Fresh Breeze

17 - 21

19 - 24

29 - 38

8 -10.7

Many white horses were formed, possibility of some spray, moderate wavers taking longer foam

Crested wavelets formed on inland water, small trees in leaf's began to sway.

6

Strong Breeze

22 - 27

25 - 31

39 - 49

10.8 - 13.8

Large waves, white form crest were extensively seen everywhere, probably some spray 

Large branches in motion, umbrellas are used with difficulties, whistling heard in telegraph wires

7

High wind, Moderate Gale, Near Gale

28 - 33

32 - 38

50 - 61

13.9 -17.1

Spindrift begins to be visible,  sea heaps up and white foam from breaking waves begins to blow in streaks along the direction of the wind.

Whole trees in motion, inconvenient to walk against wind.

8

Gale, Fresh Gale

30  - 40

39 - 46

62 - 74

17.2 - 20.7

Moderately high waves of greater length, edges of crest break into spindrift, foam is formed in well-marked streaks along the direction of the wind. 

Twigs breaking off trees, generally impedes progress

9

Strong/Severe Gale

41- 47

47- 54

75 - 88

20.8 - 24.4

High waves, dense streak of foam along the direction of the wind, sea begin to roll, spray affects visibility 

Slight structural damage occurs ( chimney, pots and states were removed)

10

Storm/ Whole Gale

48 - 55

55 - 63

89 - 102

24.5 - 28.4

Very high waves with long overhanging crests,  resulting foam in great patches is blown in white dense streak along the direction of the wind, sea take white appearance on the whole surface,  rolling of the sea becomes heavy, visibility affected

Hardly experienced inland, trees uprooted, significant structural damage.

11

Violent Storm

103 -117

28.5 - 32.6

> 64

> 73

Exceptionally high waves, a possibility for small and middle-sized ships for a long time lost to view behind the waves, the sea is covered with long white patches of foam, the edges of the wave crest were blown into foam everywhere, visibility affected

Very rarely experienced, accompanied by  extensive damage

12

Hurricane Force

> 64

<73

> 118

>32.7

The air filled with foam and spray, complete white sea with driving spray, visibly affected severely,

Devastation


Did You Know?

  • The Beaufort scale is most widely used to measure wind speed today. 

  • The Beaufort scale is named for Sir Francis Beaufort of the British Royal Navy.

  • The Douglas Sea Scale and the Douglas Wind Scale are similar to the Beaufort scale, but they separate the sea from the wind.

  • The Beaufort scale was first officially used by HMS Beagle.

  • The Beaufort scale is a method of measuring wind speed based on the general condition of the surface of a large body of water in terms of wind waves and swell.

  • The official name of the Beaufort scale is “ Beaufort Wind Force Scale”.

FAQs (Frequently Asked Questions)

1. What is the Beaufort Scale?

Ans: Beaufort Scale is an internationally recognized wind strength scale used by sailors for estimating the wind strength without the use of instruments, based on the effects wind has on the physical environment. 

2. Who discovered the Beaufort Wind Scale?

Ans: Beaufort Wind Scale is the first scale developed in 1805 by Francis Beaufort, an officer of the Royal Navy for sailors to estimate the wind speeds through different visual observations. The scale was first officially used by HMS Beagle. Initially, there were 12 levels on the scale, including 0 for “ no wind”. From 1946 to 1970, there were also Beaufort levels 13 -17. All of them were marked as hurricanes. 

3. How is Wind Speed Measured Using the Beaufort Wind Scale?

Ans: The wind speed on the Beaufort wind scale is based on the empirical relationships; v = 0.836 B3/2 m/s. Here, B is the Beaufort scale number and v is the equivalent wind speed at 10 m above the sea surface. For example, B = 9.5 is related to 24.5 m/s which is equivalent to the lower limit of "10 Beaufort".  The highest wind hurricane would be 23 in the Beaufort wind scale using this formula. 

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