Wind direction and speed
Wind is the air movement with predominant horizontal component towards the earth surface, which is generated by the horizontal pressure gradient force. It is a vector quantity which is characterised by wind speed (vector length) and its direction (vector sense). Both quantities hover considerably in time and space and, for this reason, wind is described by the terms: instantaneous and average speed (e.g. 10-minutes average speed) and wind gust. Wind gust is a sudden and short growth of wind speed.
Speed is measured in metres per second or knots, less often in kilometres per hour. When it is impossible to measure the speed with anemometer, we can estimate it with the use of the Beaufort scale, by observing our environment:
|
The |
Wind speed [m/s] |
Wind speed [km/h] |
Wind speed [kn] |
Wind description | Sea state | Land state |
|
0 |
<0,2 | <1 | <1 | Stillness | Calm | Stillness, smoke floats vertically |
|
1 |
0,3-1,5 | 1-5 | 1-3 | Draught | Ripples | Smoke is slightly disturbed by the air flow |
|
2 |
1,6-3,3 | 6-11 | 4-6 | Weak | Small waves | Leaves are waving, wind can be felt on skin |
|
3 |
3,4-5,4 | 12-19 | 7-10 | Gentle | Wave ridges are noticeable | Constant move of leaves and little twigs |
|
4 |
5,5-7,9 | 20-28 | 11-15 | Moderate | Foam on wave ridges, splash sounds | Movement of branches, floating of dust from the ground |
|
5 |
8,0-10,7 | 29-38 | 16-21 | Quite strong | Moderate waves, white, thick wave ridges, hooting sounds | Little trees are nodding |
|
6 |
10,8-13,8 | 39-49 | 22-27 | Storng | High, foamy waves, breakers and splashes are forming | Big branches are moving, wind whistle is audible |
|
7 |
13,9-17,1 | 50-61 | 28-33 | Very strong | Rough sea, sequences of foam are forming | Whole trees are nodding, movement against wind is difficult |
|
8 |
17,2-20,7 | 62-74 | 34-40 | Rapid (storm) | Moderately high waves, foam sequences | Smaller branches brake and fall from trees |
|
9 |
20,8-24,4 | 75-88 | 41-47 | Gale (strong storm) | Very high waves and sizable splashes, wave ridges start to sinuate | Fine constructions are damaged, branches are broken |
|
10 |
24,5-28,4 | 89-102 | 46-55 | Strong gale (very strong storm) | Uprooted trees, serious damages of buildings | |
|
11 |
28,5-32,6 | 103-117 | 56-63 | Rapid gale (rapid storm) | Extremely high waves, sea roaring sounds | Large damages of constructions |
|
12 |
>32,6 | >117 | >63 | Hurricane | ODeafening sea roar, very limited visibility, sea full of foam and splashes | Huge desolation |
