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Beaufort wind force scale

Specifications and equivalent speeds
Beaufort wind scale Mean Wind Speed Limits of wind speed Wind descriptive terms Probable wave height in metres* Probable maximum wave height in metres* Seastate Sea descriptive terms
Knots ms-1 Knots ms-1
0 0 0 <1 <1 Calm - - 0 Calm (glassy)
1 2 1 1–3 1-2 Light air 0.1 0.1 1 Calm (rippled)
2 5 3 4–6 2-3 Light breeze 0.2 0.3 2 Smooth (wavelets)
3 9 5 7–10 4-5 Gentle breeze 0.6 1.0 3 Slight
4 13 7 11–16 6-8 Moderate breeze 1.0 1.5 3–4 Slight–Moderate
5 19 10 17–21 9-11 Fresh breeze 2.0 2.5 4 Moderate
6 24 12 22–27 11-14 Strong breeze 3.0 4.0 5 Rough
7 30 15 28–33 14-17 Near gale 4.0 5.5 5–6 Rough–Very rough
8 37 19 34–40 17-21 Gale 5.5 7.5 6–7 Very rough–High
9 44 23 41–47 21-24 Severe gale 7.0 10.0 7 High
10 52 27 48–55 25-28 Storm 9.0 12.5 8 Very High
11 60 31 56–63 29-32 Violent storm 11.5 16.0 8 Very High
12 - - 64+ 33+ Hurricane 14+ - 9 Phenomenal

*

  1. These values refer to well-developed wind waves of the open sea.
  2. The lag effect between the wind getting up and the sea increasing should be borne in mind.
  3. To convert knots to mph multiply by 1.15, for m/s multiply by 0.514.


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