Introduction—What is the Beaufort scale?
The Beaufort scale refers to a method of estimating wind speed based on the surface condition of a large body of water in relation to wind waves and swell. The advent of the scale enables sailors to measure wind speed simply by observing the surface of the sea.
Historical perspective of the Beaufort scale
The Beaufort scale has a long history, dating back to 1805 when it was formally devised and finalized by Commander Francis Beaufort, an Irish hydrographer in the British Royal Navy, who later became an Admirer. Beaufort scale saw it first official use during Charles Darwin’s voyage on the HMS Beagle, and in 1838 the Royal Navy made it mandatory for all log entries in all British ships. The scale was later altered to include state of the sea observations and land phenomenon–the criteria that pave the way for its adoption by the International Meteorological Committee for use in international weather telegraphy.
How is the Beaufort scale used in modern times?
The contemporary Beaufort scale comes with 13 numbers which range from 0 to 12. During measurements, a Beaufort force tagged as ‘0’ is assigned to calm winds in a situation where the surface of the water is smooth. Force 12 (which is normally for hurricane and above) occurs when wave’s height is greater than 46 feet, and the sea is totally white with foam and sprays while visibility is greatly reduced. Conditions like these are because of wind speed being greater than 75mph—the typical hurricane-force winds.
Why do we still use the Beaufort scale today?
The reasons why the Beaufort scale has seen continuous use in weather forecasting is partly due to pragmatic realism. The wind has never been steady and the forecaster, who is working based on resultant wind speed from pressure gradient, is very much happy to express such variability and general uncertainty in an economic way using the Beaufort scale.
When listening to the weather forecast on the radio, it is easier to understand the difference between wind forces of 4 to 7, compared to speeds such as 13 to 30 knots.
Beaufort scale force at a glance
Force & Effect:
- Calm, no winds at all – At this time, smoke rises vertically,
- Light winds (measuring 1-5 kph or 1-3mph) – Smoke drift indicate wind direction
- Light breeze (measuring 6-11kph or 4-7mph) – Small waves on the sea, leaves rustle a bit
- Gentle breeze (measures 12-19kph or 8-12mph) – Small branches and flags will move
- Moderate breeze (measures 20-28kph or 13-18mph) – Leaves and papers are scattered
- 5 Fresh breeze (29-38kph or 19-24mph) – Common during autumn, small trees sway
- Strong breeze (39-49kph or 25-31mph) — Umbrellas become hard to use, going out become discouraging
- Moderate gale (50-61kph or 32-38mph) — It becomes difficult to walk in the wind, as whole trees sway
- Gale (62-74kph or 39-46mph) – Branches could be coming off trees, as people find it difficult to move in the wind. People may have to lean forward to brace against the wind
- Strong gale (75-88kph or 47-54mph) – Roof tiles blew off buildings and is increasingly dangerous to go out. Some people may be blown right off their feet
- Storm or whole gale (89-102kph or 55-63mph) – Whole trees are sent flying to the heavens and cars and homes could seriously be damaged.
- Violent storm (103-118kph or 64-73mph) – Widespread damage to houses and vegetation, almost zero visibility at sea
- Hurricane (measuring 119 -220kph or 74-136mph) – Unprecedented widespread destruction as cars are blown sideways, buildings are smashed, trees are uprooted from the roots, and human casualties are recorded on several occasions, depending on the hurricane category.
Estimating wind speed and the overall weather forecast is paramount to safety both at sea and on land, and the Beaufort scale has played a prominent role in this regard.
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