| 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 |