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Yachtsmen (and women) sometimes wonder why the words "perhaps gale 8 later" are used in shipping forecasts but there is no gale warning in force.
Gale Warning Rules
According to requirements placed upon the Meteorological Office, by the UK Committee for Safety of Navigation at Sea, gale warnings MUST be issued when it is known that a gale IS occurring, when it MAY occur within six or twelve hours or is CONFIDENTLY expected between twelve and twenty-four hours ahead. The terms "imminent", "soon" and "later" are used to describe the times.
Unfortunately, neither life nor the weather are simple or clear-cut and there are times when the forecaster may be in some considerable doubt as to precisely which sea areas will get gales within the forecast period and, indeed, whether the winds will reach gale force at all. There is no point in crying wolf and yet he has to be able to give some warning or indication of the uncertainty.
The "perhaps gale 8 later" formula allows him to give advance warning in a shaded sense. It really means "watch this space". This may seem somewhat pedantic to many of us, since it is as good as a warning of a gale and many would not set off on a long crossing, say across the North Sea.
Even in the imminent or soon periods there can be some uncertainty but here there is no choice. A warning has to be issued even if the forecast itself may say "perhaps gale 8 at times" or some such phrase. In order to make forecasters think carefully about gale warnings, the Meteorological Office has defined one of its performance measures for the National Meteorological Centre (formerly the Central Forecast Office) as the percentage of gale warnings that are correctly issued for the imminent and soon periods.
Many sailors in our relatively slow moving boats, would like to see warnings issued beyond twenty-four hours. The basic problem, in physical terms, is the classical one of predicting the difference between two large quantities. Wind is caused by relatively small differences in barometric pressure. A small rise in the pressure over Northern France and a slight fall over Ireland could make all the difference between a nice force 4, an uncomfortable force 6 and a three reef, storm jib force 8.
An exception is in the Western Mediterranean where the Spanish Met Service does issue gale warnings up to about three days ahead. The French also give warnings using words like "menace de coup de vent" well in advance. They are able to do this because the conditions for such winds as the Mistral and the strong winds through the Gibraltar Strait are easy to forecast. To the sailor, the winds may appear to set in suddenly but the conditions in terms of the pressure pattern are well known. Modern computerised forecasting makes the prediction straightforward.
Unfortunately, the same is not true for Atlantic depressions. But, even here, it is my opinion that forecasters could - and should - give more warning of gales than at present. They could always use the "Perhaps" formula or some other wording because of the inherent uncertainties. Forecasting is sufficiently good these days for useful advice to be given of this nature. Bets advice, for now, is to use the three to five day outlooks on NAVTEX 518 kHz and the BBC website. Sailors will find GRIB files are also useful for this purpose.
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