The popular concept of "equinoctial gales" would have us believe that very strong winds are more frequent in late March and late September than at any other time of year. Statistics, however, do not support the theory. Records show that January and December are the windiest months, and that gales in the North Atlantic are most frequent then than at either of the equinoxes.
What the statistics do tell us, however, is that there is an abrupt increase in the average frequency of high winds during the second half of September. It is not uncommon, therefore, for mid-September to provide the first real gale of the winter season, and this may account to some extent for the "guilt by association" of the equinox.
Another factor has enhanced the reputation of the weeks around the autumnal equinox as a windy period. Despite winds which sometimes howl at Hurricane Force, or Force 12 on the Beaufort Scale, hurricanes in the strict scientific sense of the word do not happen at these latitudes. Hurricanes needs a warm and humid ambience to survive, and typically thrive over oceans where the water temperature is in excess of 26 C. Once a hurricane moves northwards its ferocity rapidly diminishes.
Sometimes, however, long after the winds of a Caribbean hurricane have died away, a quantity of unusually warm and moist air frequently survives, concentrated into a relatively small region of the upper atmosphere to be carried into the mid-Atlantic. If this warm humid air is absorbed into the circulation of an ordinary North Atlantic depression, it may add enough extra energy to cause a dramatic intensification of the low. The worst September gale experienced in living memory on this island had its origins in this kind of process: the event that we recall as Hurricane Debbie took place 40 years ago yesterday on September 16th, 1961.
Debbie had been born as a hurricane in the balmy waters of the Caribbean five or six days previously. Its intensity abated as it turned northwards over the colder waters of the North Atlantic, but by the time the storm reached these islands it had acquired a new lease of life. As it passed near the north-west coast of Ireland, Debbie caused great damage in the western half of the country, bringing winds with gusts in excess of 100 miles per hour. At many places in this country, the record for the highest windspeed ever recorded was established on that memorable day 40 years ago.