By Len Shaffrey, National Centre for Atmospheric Science, University of Reading

Ireland’s location on the northwestern edge of Europe means that it has long been subjected to the strong winds and heavy rain from storms that sweep in from the north Atlantic Ocean. The most severe of these storms can be devastating. Events such as Oíche na Gaoithe Móire (the Night of the Big Wind) on 6 January 1839 resulted in high winds and heavy seas that led to several hundred deaths, the sinking of 42 ships and severe damage to property across Ireland. For example, up to a quarter of the houses in North Dublin were reported to have been damaged or destroyed.

In October 2017, Ireland was once again in the path of a major storm. Storm Ophelia was making its way past the Portuguese coast and heading for the south coast of Ireland. The path and severity of Storm Ophelia was very well forecast enabling early warnings of the oncoming storm to be issued days in advance. Nonetheless, when Ophelia hit, it brought devastating winds to Ireland with 119 mph gusts recorded at Fastnet Rock. The storm sadly caused three fatalities and left 360,000 without power.

Storm Ophelia was unusual in a number of ways. It started life as a Tropical Cyclone in the Atlantic and intensified to become a Major Hurricane on 11 October. Ophelia continued to gain strength and then started to move north-east towards Ireland. As it moved over colder waters and began to interact with the North Atlantic jet stream, Ophelia transitioned into powerful extratropical storm. It eventually hit Ireland on the 16 October.

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Storms like Ophelia are known as tropical-extratropical transitions as they start out as a tropical storm and then move into the extratropics. While it is relatively rare for them to make landfall in Europe, they can have substantial impacts when they do.

For example, Ex-Hurricane Debbie in September 1961 inflicted severe wind damage across Ireland and caused 18 fatalities, whilst the heavy rainfall from Ex-Hurricane Charley in August 1986 broke several Irish rainfall records and led to severe flooding. Ophelia was also unusual in another way, since it was the most eastern Major Hurricane recorded in the Atlantic.

A key question is why did Ophelia retain its Hurricane-like structure for so long before becoming an extratropical storm? One possible reason is that subtropical North Atlantic Ocean was anomalously warm throughout the second half of 2017. The warmer water may have allowed Ophelia to travel further eastwards and northwards than usual.

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This also raises the possibility that the warming of the oceans due to climate change may lead to an increased occurrence of tropical-extratropical transitions in the future. Given their impacts, developing our understanding of the current and future risks from storms such as Ophelia is essential.

The Wind That Shakes The Island is an event hosted by the Irish Meteorological Society and Met Éireann which will discuss the latest scientific understanding of such storms and focus on the challenges of forecasting Storm Ophelia. Speakers will include Met Éireann's Evelyn Cusack and Liz Walsh and Dr. Mike Brennan of the U.S. National Hurricane Center in Miami. I’ll be covering what science can tell us about how climate change might affect severe storms in the future. The event will be held on Friday 13 April at the RDS in Dublin and is admission is free.

Professor Len Shaffrey is Professor of Climate Science at the National Centre for Atmospheric Science at University of Reading


The views expressed here are those of the author and do not represent or reflect the views of RTÉ