II. The Atmosphere

8. Beaufort scale

The force of wind is usually represented by a wind force scale. The scale can be estimated by measuring the movement of objects blown by wind at the surface of the land or sea. The current internationally used standard scale of wind force estimation is called the Beaufort scale. The name comes from Admiral Beaufort of the British Navy, who established the scale in 1805. At first it was only used over the sea, but later it was extended for use over land. After several amendments it became the general measure of wind force used today.

Tab. 1: Beaufort scale for land use

Beaufort Force Wind Description Wind Effect Description m/s kts
0 calm Smoke rises vertically. less than 0.3 less 1
1 light air Smoke drift indicates wind direction, still wind vanes. 0.3-1.5 1-3
2 light breeze Wind felt on face, leaves rustle, vanes begin to move. 1.6-3.3 4-7
3 gentle breeze Leaves and small twigs constantly moving, light flags extended. 3.4-5.4 8-12
4 moderate breeze Dust and loose paper lifted, small tree branches move. 5.5-7.9 13-16
5 fresh breeze Small trees in leaf begin to sway. 8.0-10.7 17-21
6 strong breeze Large tree branches moving, whistling in wires. Umbrella use becomes difficult. 10.8-13.8 22-27
7 near gale Whole trees in motion, resistance felt when walking against the wind. 13.9-17.1 28-33
8 gale Twigs broken from trees. Progress generally impedes. 17.2-20.7 34-40
9 strong gale Slight structural damage occurs. Chimney post removed. 20.8-24.4 41-47
10 storm Trees uprooted. Considerable structural damage. 24.5-28.4 48-55
11 violent storm Extremely rare. Widespread damage. 28.5-32.6 56-63
12 hurricane - 32.7-36.9 64-71
13 - - 37.0-41.4 72-80
14 - - 41.5-46.1 81-89
15 - - 46.2-50.9 90-99
16 - - 51.0-56.0 100-108
17 - - 56.1-61.2 109-118