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Beaufort Wind Scale


   Written by: CHIU Hung-yu


  1. "Beaufort wind scale" or "Beaufort wind force scale" was created by British Admiral Sir Francis Beaufort in 1805. At that time, ships included fishing boats and warships, where canvas sails were deployed to ride the waves using wind power. Anemometer was not yet available. 

    Wind and waves are inter-related. The stronger the winds, the higher will be the waves.  The wind strength has direct influence on the state of the sea. Beaufort developed the scale based on experience and observations on board a warship (called "44 gun man-of-war"). The scale is in form of a table grading the wind strength from force 0 to force 12 (totally 13 categories). 

    The Beaufort wind scale was originally drawn up to relate the number of canvas sails required to each category of the  wind forces.  The higher the wind force, the less canvas sails would be required.

    The Beaufort wind scale was revised several times. In 1906, the description was extended from sea state to land observations of objects being blown by winds. In 1926, a set of equivalent wind speeds corresponding to the Beaufort wind force scale was adopted. In 1947, reporting of wind velocity in knots was agreed by the International Meteorological Organization. Description of the sea state and effects on land according to the different Beaufort wind forces (and equivalent velocities) can be accessed here.

    In 1946, the wind scale was expanded with the addition of wind forces 13 to 17. However, the expanded scale is not widely used.


  1. Beaufort scale
    number
    Description Mean wind velocity in knots Mean wind 
    velocity in

    km/hour
    Illustration
    0 Calm <1 < 2 F0
    1 Light 1-3 2 - 6 F1
    2 4-6 7 - 12 F2
    3 Moderate 7-10 13 - 19 F3
    4 11-16 20 - 30 F4
    5 Fresh 17-21 31 - 40 F5
    6 Strong 22-27 41 - 51 F6
    7 28-33 52 - 62 F7
    8 Gale 34-40 63 - 75 F8
    9 41-47 76 - 87 F9
    10 Storm 48-55 88 - 103 F10
    11 56-63 104 - 117 F11
    12 Hurricane >=64 >= 118 F12
    Table 1.  The Beaufort Wind Scale
   References:
  1. COADS Project Report: Early Data Digitization and United States Code History, by Joe D. Elms, 1995, National Climatic Data Center, NOAA, USA.
  2. The Origin of Wind, HKO e-Bulletin on Educational Resources, Issue No.2 (July 2004).
  3. Wikipedia.

Last revision date: <01 Apr 2014>