It has been a very busy storm season since the meteorological year began in September with five to date, an average of one a month.
Storm Éowyn was distinguished by its unprecedented power. As predicted accurately by weather forecasters, it was one of the most powerful storms to have ever hit Ireland.
Fortunately, most of the worst winds were during the night-time and there were no fatalities.
Storm Éowyn arose out of a class of frigid air in the northeast of the United States which caused president Donald Trump’s inauguration to be staged indoors.
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It met warmer air from the tropics. The two together created a very powerful and fast-moving jet of air. This low-pressure system got picked up in turn by the jet stream, which powered its way over Ireland.
Off the coast, atmospheric pressure in the centre of the storm dropped very rapidly, a process known as cyclogenesis. Pressure dropped from 985hPa to 935hPa in Co Mayo, creating tightly packed isobars associated with strong wind.
The most extreme gust was the 183km/h at Mace Head, Co Galway, at 5am – a record for Ireland – along with the highest continual wind at 131km/h, which was also a record.
“We think there was a sting jet associated with a very active low-pressure system. This is a core of very strong winds which get accelerated down from the troposphere to the surface,” explained Met Éireann forecaster Liz Coleman.
“They are very hard to prove, but there is some evidence in the satellite data that that occurred at the Mace Head location.”
A sting jet is a column of air which resembles a scorpion’s tale on satellite imagery. It is a narrow column of air, only 30km across at a maximum, and its impact is usually localised. It may account for the record-breaking value at Mace Head not being replicated elsewhere. The next highest gust was at Knock airport, which recorded 155km/h at 6am, followed by Finner in Co Donegal which recorded a wind speed of 144km/h.
Another storm system is crossing the Atlantic this weekend. Storm Hermonie has been named by the Spanish meteorological office.
It will mostly impact Spain, but there is a possibility of it bringing strong winds and rain to the south of Ireland and there is an expectation that there will be yellow weather warnings issued for Sunday.
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