Wind Strength

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The Beaufort Scale of Wind Strength

Force 0. 1 mph or less. Calm. The air feels still and smoke rises vertically.

Force 1. 1–3 mph. Light air. Wind vanes and flags do not move, but rising smoke drifts.

Force 2. 4–7 mph. Light breeze. Drifting smoke indicates the wind direction.

Force 3. 8–12 mph. Gentle breeze. Leaves rustle, small twigs move, and flags made from lightweight material stir gently.

Force 4. 13–18 mph. Moderate breeze. Loose leaves and pieces of paper blow about.

Force 5. 19–24 mph. Fresh breeze. Small trees that are in full leaf wave in the wind.

Force 6. 25–31 mph. Strong breeze. It becomes difficult to use an open umbrella.

Force 7. 32–38 mph. Moderate gale. The wind exerts strong pressure on people walking into it.

Force 8. 39–46 mph. Fresh gale. Small twigs are torn from trees.

Force 9. 47–54 mph. Strong gale. Chimneys blown down, slates and tiles torn from roofs.

Force 10. 55–63 mph. Whole gale. Trees are broken or uprooted.

Force 11. 64–75 mph. Storm. Trees are uprooted and blown some distance. Cars are overturned.

Force 12. More than 75 mph. Hurricane. Devastation is widespread. Buildings are destroyed, many trees uprooted. In the original instruction, ‘no sail can stand’.

Saffir/Simpson Hurricane Scale

Category Pressure at centre (inches of mercury) Wind speed (mph) Storm surge (feet)

1 28.94 74–95 4–5

2 28.5–28.91 96–110 6–8

3 27.91–28.47 111–130 9–12

4 27.17–27.88 131–155 13–18

5 below 27.17 more than 155 more than 18

Fujita Tornado Intensity Scale

Rating Wind speed (mph) Damage expected

F-0 40–72 Light damage

F-1 73–112 Moderate damage

F-2 113–157 Considerable damage

F-3 158–206 Severe damage

F-4 207–260 Devastating damage

F-5 261–318 Incredible damage

From A Dictionary of Earth Sciences in Oxford Reference.

Subjects: Earth Sciences and Geography.

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