There storm Éowynafter growing very rapidly in the North Atlantic, hit theIreland with hurricane force winds and gusts up to 185 km/h recorded at Mace Head, County Galway, beating the previous Irish record of 182 km/h which had stood since 1945. It is one of the most violent storms ever recorded in the country, on which an activered alert for today.
Éowyn’s passage is bringing Ireland to its knees, where high waves have also been recorded 12 metersbeyond 700,000 buildings they were left without electricity, public transport was disrupted and more 220 flights departing and arriving from Dublin Airport have been cancelled. According to local authorities, the cyclone is causing “unprecedented damage” and is currently headed towards the Scotland.
In Italy we will feel alone marginally the effects of Éowyn: the Centre-North, in particular the Tyrrhenian side, will be affected by the flow of humid air at the edge of the cyclone. However, it is possible that next Monday and Tuesday (27-28 January) a new storm of Atlantic origin will reach the British Isles with possible effects on our country too.
Weather-wise, Éowyn it’s not a hurricane: these atmospheric phenomena “live” in fact in tropical latitudes. In technical jargon we talk about extratropical cyclonei.e. a low pressure area (Éowyn is at 940-945 hPa) rotating but outside the tropical belt.
In particular, the journalistic term for storms like Éowyn is “bomb cyclone”that is, an extratropical cyclone that intensifies very rapidly, with a decrease in its central pressure of at least 24 hPa within 24 hours. The technical term used in meteorology to describe what is happening is instead explosive cyclogenesis. In Éowyn’s case we are talking about a possibility 55 hPa drop in 24 hoursaccording to the forecasts of the English meteorological service: it is one of the most intense explosive cyclogenesis ever recorded in the British Isles.
But how is it possible that Éowyn reached intensities comparable to those of a hurricane despite having formed in the North Atlantic and moreover outside the hurricane season? Generally, explosive cyclogenesis occurs in the presence of a rapid clash between cold and warm currents between which there is a high temperature difference. In Éowyn’s case, this sudden thermal contrast also occurred thanks to the contribution of jet streaman almost permanent system of strong winds at very high altitudes that follow a closed path in a west-east direction. The freezing air in this case came from the USA, where it contributed to the snowfall in Florida in recent days.