|
Force
|
Description
|
Result
|
Wind speed
|
|
mph
|
Knots
|
|
0
|
Calm
|
Smoke rises vertically
|
0-1
|
<1
|
|
1
|
Light air
|
Wind direction indicated by smoke but not wind vanes
|
1-3
|
1-3
|
|
2
|
Light breeze
|
Wind noticeable, leaves move, wind vane moves.
|
4-7
|
4-6
|
|
3
|
Gentle breeze
|
Leaves and small twigs in constant motion.
|
8-11
|
7-10
|
|
4
|
Moderate breeze
|
Wind raises dust and loose paper. Small branches are moved.
|
12-18
|
11-16
|
|
5
|
Fresh breeze
|
Small trees in leaf start to sway. Crested wavelets form on
inland waters.
|
19-24
|
17-21
|
|
6
|
Strong breeze
|
Large branches in motion, wind whistles. Umbrellas used with
difficulty.
|
25-31
|
22-27
|
|
7
|
Near gale.
|
Trees in motion, awkward to walk against wind.
|
32-38
|
28-33
|
|
8
|
Gale
|
Twigs break, hard to walk.
|
39-46
|
34-40
|
|
9
|
Strong gale
|
Some structural damage may occur, slates removed etc.
|
47-54
|
41-47
|
|
10
|
Storm
|
Trees uprooted, considerable
structural damage.
|
55-63
|
48-55
|
|
11
|
Violent storm
|
Widespread damage.
|
64-72
|
56-63
|
|
12
|
Hurricane
|
Widespread damage.
|
72+
|
>63
|