Following on from the coldest Winter since 1962-63 and the coldest Spring since 1962, Summer 1979 wasn't anything to write home about. It was cool, wet and dull but not exceptionally so, therefore a very forgettable Summer in the sense of the overall statistics. However, this season stands out for one single event that occurred in mid-August 1979. This was of course the Fastnet Storm.
From a synoptic stand point, what happened was that a depression of approximately 1010mb at this time near Newfoundland in Canada moved eastwards over the North Atlantic Ocean on the 11th/12th August. Rather than the low filling and weakening, it did the opposite with it intensifying as it got closer to Ireland. The low pushed into the southwest of Ireland on the night of the 13th being directed northeastwards over the country. At midnight on the 14th, minimum pressure dropped to 984mb in contrast to the pressure being 1010mb at 16:00 on the 13th. This was a 26mb drop in pressure in an 8-hour period and it was officially a "weather bomb" or in scientific terms, explosive cyclogenesis. What defines a weather bomb is that the pressure of a low drops at least 21mb within a 24-hour period and in this case, the pressure dropped 26mb from 1010 to 984mb within 8 hours! Many of the storms or weather bombs you know of in recent times like say the 9/10 December 2014 or 23 December 2013 have their pressure dropping gradually over the 24-hour period but in August 1979, the pressure dropped very rapidly which led to high seas and unseasonably windy conditions.
From Met Éireann:
Our stations near the south coast (Valentia Observatory, Roche's Point, Cork Airport and Rosslare) all reported winds of near gale or gale force (force 7 or force 8 respectively) with gusts in the range 46 to 52 knots (1 knot = 1.15 mph = 0.515 m/s). However, the maps show the strongest winds just off the south coast where yachtsmen were reporting storm or violent storm force winds with even a suggestion of hurricane force winds (force 12). The winds recorded at the land stations would suggest winds at sea just about reaching storm force 10 but force 11 or force 12! Well the supplementary sources of information, the Fastnet lighthouse, the naval vessel Deirdre and the Marathon Gas Platform, indicate that the yachtsmen did not exaggerate.
Forecast guidance did not convey either the severity of the conditions or the speed with which they developed but then such explosive deepening is very difficult to forecast. However, predictive ability has improved considerably since 1979 and so we may hope that warnings will be more timely and accurate in future.
The maximum wave height recorded at The Marathon Gas Platform was 14.5 metres. In comparison, Storm Darwin of 12 February 2014 caused a maximum wave height of 25m at the Kinsale Energy Gas Platform. August 1979's wave height may not seem that extreme here compared to Darwin but you got to remember that a race was taking place and not to mention, this was in the Summer season.
Look how the low evolves.
Satellite for near midday on 14th August 1979.
Hundreds of yachts were lost and unfortunately, there were 15 fatalities courtesy of the storm.
Was it unprecedented? No. Summer storms like it have happened before and have happened since. They are rare due to the weak zonal flow in Summer time. Two other examples of Summer storms include the one in July 1956 and in July 1988. This storm was so tragic and eventful because it coincided with the Fastnet Yacht Race.
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