Why Do Wind Gusts Make Headlines?
By Paul Homewood
As many have pointed out, the use of wind gust speeds seems to have become more prevalent recently, and can lead to an overinflated impression of the strength of a storm.
The BBC has even built gusts into their forecasts, explaining:
Frankly, I find their excuse pathetic. It is in fact thoroughly confusing seeing their forecast suddenly switch from 18 mph to 40 mph – what does this mean in reality?
According to the Met Office:
Measuring gusts and wind intensity
Because wind is an element that varies rapidly over very short periods of time it is sampled at high frequency (every 0.25 sec) to capture the intensity of gusts, or short-lived peaks in speed, which inflict greatest damage in storms. The gust speed and direction are defined by the maximum three second average wind speed occurring in any period.
A better measure of the overall wind intensity is defined by the average speed and direction over the ten minute period leading up to the reporting time. Mean wind over other averaging periods may also be calculated. A gale is defined as a surface wind of mean speed of 34-40 knots, averaged over a period of ten minutes. Terms such as ‘severe gale’, ‘storm’, etc are also used to describe winds of 41 knots or greater.
I don’t know how long our technology has been able to measure at quarter second intervals, but this alone must lead to an inflation of gust speeds over older equipment.
It is of course the 10 minute sustained speeds which are used for the well established Beaufort Scale.
I am not aware that the Met Office has published any official Beaufort data for Abigail, but sustained speeds would probably be at least 20 mph less than gusts, making it Storm Force 10 on the Beaufort Scale at its strongest in the Hebrides, Orkney and Shetland. Elsewhere in Scotland, I doubt it made more than a Severe Gale.
[The Scale goes up to 12, which is hurricane strength]
One of the effects of this obsession with is that it allows news outlets regularly to talk about “hurricane strength” winds. This is absolute nonsense, as hurricane strength scales are all based on sustained wind speeds, not gusts.
For instance, the Saffir-Simpson scale, which is based on 1-minute sustained speeds, only categorises a storm as a hurricane when it reaches 74 mph. Even at South Uist, it is highly unlikely the Abigail ever reached anywhere near that.
The Beaufort Scale has been around since 1805, and has real and critical significance for those who use it. To see it bypassed just for spectacular headlines is short sighted and sums up so much of the reporting of weather/climate issues these days.