Admiral Sir Richard Beaufort devised his scale for wind speed in 1805 to permit standardized reporting of wind conditions.
Measurement:
• Wind speed measurement is performed at a point 10 meters above the surface of ground or water.
Wind Speed in miles per hour |
Wind Speed in Knots |
Beaufort Number |
Name |
0 |
0 |
0 |
calm |
1 - 3 |
1 - 3 |
1 |
light air |
4 - 7 |
4 - 6 |
2 |
light breeze |
8 - 12 |
7 - 10 |
3 |
gentle breeze |
13 - 18 |
11 - 16 |
4 |
moderate breeze |
19 - 24 |
17 - 21 |
5 |
fresh breeze |
25 - 31 |
22 - 27 |
6 |
strong breeze |
32 - 38 |
28 - 33 |
7 |
moderate gale |
39 - 46 |
34 - 40 |
8 |
fresh gale |
47 - 54 |
41 - 47 |
9 |
strong gale |
55 - 63 |
48 - 55 |
10 |
whole gale |
64 - 73 |
56 - 63 |
11 |
storm |
>= 74 |
>= 64 |
12 - 17 |
hurricane |
where:
• 1 knot = 1.1516 miles per hour
Beaufort Number |
Appearance On Land |
Appearance At Sea |
0 |
smoke rises straight up |
glassy appearance |
1 |
smoke drifts in direction of wind |
ripples but no wave crests |
2 |
leaves rustle bout, wind felt in face |
small crests that do not break |
3 |
leaves move, light flags wave |
crests start to break, large wavelets |
4 |
small branches move; dust and paper blown about |
small waves, some with whitecaps |
5 |
small trees bend |
moderate waves, many with whitecaps |
6 |
difficulty in holding umbrellas, large tree limbs move |
large waves, with spray |
7 |
walking difficult, large trees bend |
large waves breaking with white foam |
8 |
walking very difficult, trigs break |
moderately high waves breaking into foam and spindrift forms |
9 |
loss of roof shingles |
high waves, sea rolls, dense foam |
10 |
moderate damage to buildings; trees uprooted |
very high waves, blowing foam, heavy rolling seas |
11 |
widespread damage |
sea covered with foam, extremely high waves |
12 - 17 |
violent and destructive |
poor visibility, air filled with spray and foam |
Specialty: Emergency Medicine, Critical Care