It could be said of Sunday's southern rains, as the historian de Tocqueville remarked about the Revolution, that "never was any such event so inevitable, yet so completely unforeseen." The genesis of the deluge is to be seen on the weather maps of preceding days as an innocuous ripple, or "wave" as meteorologists like to call them, on a slow-moving front stretching from the Atlantic, south of Ireland, into northern France.
This minor disturbance was expected to slide harmlessly eastwards, expiring slowly as it headed towards the English Channel; instead it deepened quickly and unexpectedly into a full-blown depression, and deposited many tons of water on the southern half of Ireland.
This is a normal enough occurrence in the meteorological scheme of things. Usually, however, the processes that allow one such wave to acquire an energy denied its fellows, causing it to deepen rapidly, can be identified and the results predicted. On this occasion it seems that the computers missed the signal, and the reasons why will no doubt be the subject of investigation in the coming weeks, providing lessons for the future.
There was, in a way, a sense of deja vu about this August deluge. Eighteen years ago forecasters were taken by surprise by another August storm, the "Fastnet Storm" of August 13th, 1979, that wreaked havoc with yachts participating in the Fastnet Race. Although remarkable more for the ferocity of its winds, it shared with Sunday's episode its geographical location and the fact that it was improbable, unexpected, unforeseen.
The amount of rain involved in Sunday's downpour - something like an average monthly total in a 24-hour period - are unusual, even extreme, but not unprecedented.
Many of us remember the torrential rains of Hurricane Charley back in 1986: that set many records that are still unequalled. The fact is that August rains have a natural tendency to heaviness; the warm summer atmosphere is capable of accommodating moisture in great quantities, so that when conditions otherwise are ripe for rain, the quantities that fall are often large.
Although the underlying causes of the heavy rain may still require investigation, there are a number of factors that can be dismissed. Firstly, the event had no connection whatsoever with the recent floods in eastern Europe; it was an entirely separate and independent happening.
Secondly, we have no need to look to global warming for an explanation, since we have often had such quantities of rain before. And thirdly, the recent resurgence of El Nino in the faraway Pacific is irrelevant to the development of this single, isolated, yet in the end quite ordinary, storm.