Beaufort wind force scale
The Beaufort scale, which is used in Met Office marine forecasts, is an empirical measure for describing wind intensity based on observed sea conditions.
| 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 | Strong 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 | |
- These values refer to well-developed wind waves of the open sea.
- The lag effect between the wind getting up and the sea increasing should be borne in mind.
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