Classifying Wind Speed
Wind speed can be given according to the Beaufort Scale mainly used to report weather at sea, "a force 9 gale" for example. On land, various indicators such as the movement of smoke or branches, enable the wind speed to be estimated with reasonable accuracy.

• Force 1: 3 km/h (2 mph) smoke drifts
• Force 2: 9 km/h (5 mph) leaves rustle
• Force 3: 15 km/h (10 mph) flags flutter
• Force 4: 25 km/h (15 mph) small branches move
• Force 5: 35 km/h (21 mph) small trees sway
• Force 6: 45 km/h (28 mph) large branches move
• Force 7: 56 km/h (35 mph) whole trees sway
• Force 8: 68 km/h (43 mph) twigs break
• Force 9: 81 km/h (50 mph) branches break
• Force 10: 94 km/h (59 mph) trees blow down
• Force 11: 110 km/h (69 mph) serious damage
• Force 12: 118 km/h (74 mph) hurricane damage

Why is it important?
Admiral Sir Francis Beaufort (1774-1857 devised his wind scale in 1806. Born in Northern Ireland, he served in the Royal Navy and became their hydrographer (scientist of the sea). His scale was adopted for use at sea in 1838 and by 1874 it was adopted internationally.