Ocean warming may be behind remnants of hurricanes hitting Ireland more often

There is an emerging pattern of remnants of hurricanes hitting Ireland more frequently. Their impact is being compounded by more extreme rainfall and higher seas compared to typical Atlantic storms.

What may soon become the new norm is already highlighting how ill-prepared the country is for such weather events. There are insufficient adaptation measures in place to counter their destructive effects, notably on coastlines, according to climatologists.

They cite “early evidence” that hurricane-force storms like Lorenzo and Ophelia will reach Ireland more often from the east coast of America, although some recent ones have turned right in the mid-Atlantic and headed towards the European continent.

Other research indicates hurricanes will become more intense in the future due to rising sea temperatures. This trend in rising sea temperatures over most of the Atlantic is a prime driver of this; yet another indication of human-induced climate change.

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What's more it's also encouraging storms to stall, giving them even more time to dump vast amounts of water on reaching land, as happened with Storm Dorian over the Bahamas recently.

Similarly, melting ice sheets due to global heating are leading to an acceleration of sea-level rise that make storm surges more ferocious.

There is some evidence that extra-tropical storms – large-scale low pressure weather systems (cyclones) that occur in the middle latitudes – are going further north and sometimes further east. In the Atlantic that means moving towards Ireland, says climatologist Dr Kieran Hickey of UCC geography department.

This is particularly discernible with the leftovers of hurricanes during the late August to October period. He believes this pattern goes back to the 20th century. What is of concern, however, is that Ophelia (a category 3 hurricane) went so far north and east in the Atlantic, while Lorenzo (category 5) is going even further in this direction – “that’s two in the past three years”.

He warns that even if they fade out as hurricanes their impact can be immense. Lorenzo stretches over 500km and is accelerating towards Ireland though it is weakening.

Turn right

As sea temperatures rise these form of storms are more likely but in his view it will be gradual – “probably not every year”.

As to why some hurricanes turn right before reaching the Caribbean or southern US, that question has yet to be answered. Modelling to predict how hurricanes behave with certainty is extremely challenging; “like trying to put an instrument on a cloud”.

On rainfall quantities, Dr Hickey s says the “warm cores” of hurricanes mean they can contain much more moisture that falls as they meet cooling waters higher up in the Atlantic. The higher the temperature the more they trap.

Meanwhile, for every degree the globe warms, the atmosphere can hold 7 per cent more water vapour. The inevitable consequence is yet more rainfall.

Dr Barry O'Dwyer, who is also based at UCC and leads the Climate Ireland programme which works with local authorities on adaptation measures, says the critical need to adapt in response to new trends has yet to be properly addressed.

“We can expect more Storm Lorenzos. Ocean warming is leading to these storms travelling further. Storms will track this direction more often. This is a sign of things to come. Ireland is not ready for the future – we need to start planning now. Our coastal areas are at substantial risk.”

Dr Eimear Cotter, director of the office of environmental sustainability at the Environmental Protection Agency, echoes concern about the vulnerability of Irish cities near coastlines, and underlines the benefit of examining what other places are already doing.

“Cities such as San Francisco are developing sophisticated tools to understand the combined impact of sea level rise, severe storms and flooding which address these challenges in an integrated way. We need similar tools for Ireland’s cities and coastline to manage and adapt to the impacts of climate change.”

Storm surges

In the San Francisco Bay area the Adapting to Rising Tides programme is an online resource helping communities prepare for the impacts of current and future flooding due to sea level rise and storm surges.

They learn about the causes of flooding, while exploring maps of flood risk along their shoreline and are provided with data tools for further analysis.

Dr Cotter says these maps increase understanding of what could be at risk without future planning and adaptation. This helps communities, government and businesses to drive action and plan appropriately.

Dr Hickey notes that recent hurricanes have impacted differently on Ireland. Debbie brought record wind speeds, Charlie brought 24-hour rainfall, while Ophelia brought record waves of “a non-standard height”.

“We have not had all three. That would be catastrophic for Ireland.”