THE deep depression that caused yesterday's storm developed in mid-Atlantic cover the weekend. During the first half of Tuesday it deepened rapidly to 960 hectopascals and moved eastwards, just south of Ireland, towards Land's End. Most late autumn or winter depressions affecting this island pass close to our north-west coast, tracking north-eastwards in the general direction of Norway, but now and then, like yesterday, one of them passes to the south, and this has several unwelcome implications.
Firstly, since winds blow in an anti clockwise direction around a low, Ireland is subjected in such circumstances to an onslaught of strong easterly winds. Frequently in such a situation the west of the country, accustomed to winter gales, is relatively sheltered and escapes the worst, while the eastern seaboard bears the brunt of the heavy seas and storm-force winds.
Secondly, when depressions follow their normal track the rain-bearing fronts on their southern flank are swept rapidly across the country. The fronts wrapped around the northern perimeter of a depression to the south, however, linger for half a day or more over affected areas, so rainfall totals tend to be high and floods are not at all uncommon.
And thirdly, at this time of year easterly winds nearly always mean low temperatures, since the air on its journey towards us has passed over the cold land-surfaces of northern Europe. Sometimes, as happened yesterday, its temperature may not be too far above freezing point, and the precipitation in some areas, therefore, may fall in the form of sleet or snow.
But, at least in an era of fears about a changing climate, we can console ourselves that it has all happened before. Yesterday's Weather Eye, you may recall, told the story of the Prince of Wales and the Rochdale, two ships that came to grief in Dublin Bay when severe blizzards affected the entire east coast 189 years ago to the very day, on November 19th, 1807. And it was also on November 19th, this time back in 1316, that the belfry of Christ Church Cathedral was blown down in a severe gale, and many other buildings in Dublin were laid low by storm-force winds.
In another November gale, that of 1637, "in one night 10 or 12 barks" were blown from their anchorage in Dublin Bay, "of the most part whereof no news hath been heard since". And, in November 1797, the problem, as was the case in parts of Dublin yesterday, was flooding houses in Patrick Street were under several feet of water and rowing-boats were used to negotiate the Castle Yard.