If a wind measuring instrument (anemometer) becomes faulty or is not available, wind can be estimated by visual means such as observing smoke as a guide to wind speed and using the Beaufort Scale (Table 4.2).
It is also possible to estimate wind direction by observing the flow of smoke or the movement of a flag. Streamers at airports can also be used when the wind speed is high enough.
When wind is monitored visually (without anemometer), the following points should be noted:
*Stand directly under the indicator to eliminate any perspective-related errors.
*Do not mistake local eddies resulting from the surrounding conditions (buildings, for example) for the general wind direction.
*Do not use the direction of cloud movement as an indicator even if their altitude seems low.
| Description | Wind speed (kt) | Wind speed (m/s) | Wind speed (Km/h) | Wind speed (mph) | Specs for estimating speed over land | |
| 1 | Calm | < 1 | 0 – 0.2 | < 1 | < 1 | Calm; smoke rises vertically. |
| 2 | Light air | 1 – 3 | 0.3 – 1.5 | 1 – 5 | 1 – 3 | Direction of wind shown by smoke-drift but not by wind vanes. |
| 3 | Light breeze | 4 – 6 | 1.6 – 3.3 | 6– 11 | 4 – 7 | Wind felt on face; leaves rustle; ordinary vanes moved by wind. |
| 4 | Gentle breeze | 7 – 10 | 3.4 – 5.4 | 12 – 19 | 8 – 12 | Leaves and small twigs in constant motion; wind extends light flags. |
| 5 | Moderate breeze | 11 – 16 | 5.5 – 7.9 | 20 – 28 | 13 – 18 | Raises dust and loose paper; small branches are moved. |
| 6 | Fresh breeze | 17 – 21 | 8.0 – 10.7 | 29 – 38 | 19 – 24 | Small trees in leaf begin to sway, crested wavelets form on inland waters. |
| 7 | Strong breeze | 22 – 27 | 10.8 – 13.8 | 39 – 49 | 25 – 31 | Large branches in motion; whistling heard in telegraph wires; umbrellas used with difficulty |
| 8 | Near gale | 28 – 33 | 13.9 – 17.1 | 50 – 61 | 32 – 38 | Whole trees in motion; inconvenience felt when walking against the wind. |
| 9 | Gale | 34 – 40 | 17.2 – 20.7 | 62 – 74 | 39 – 46 | Breaks twigs off trees; generally impedes progress. |
| 10 | Strong gale | 41 – 47 | 20.8 – 24.4 | 75 – 88 | 47 – 54 | Slight structural damage occurs (chimney-ports and slates removed). |
| 11 | Storm | 48 – 55 | 24.5 – 28.4 | 89 – 102 | 55 – 63 | Seldom experienced inland; trees uprooted; considerable structural damage occurs. |
| 12 | Violent storm | 56 – 63 | 28.5 – 32.6 | 103 – 117 | 64 – 72 | Very rarely experienced; accompanied by widespread damage. |
| 13 | Hurricane | 64 and over | 32.7 and over | 118 and over | 73 and over | – |