Sunday 18 March 2018

The story of a hurricane and of the Met experts who tracked it

As Ophelia headed towards Ireland, forecasters worked around the clock to keep an eye on the volatile visitor, writes Maeve Sheehan

Taoiseach Leo Varadkar traverses a ditch in Drumlargan
Taoiseach Leo Varadkar traverses a ditch in Drumlargan
Maeve Sheehan

Maeve Sheehan

Dr Sandra Spillane spent last Sunday holed up in her home office studying the evolving mass that was Storm Ophelia on her computer screen. A climatologist with Met Eireann with a Phd in maths, she was "literally looking back in time" to find something comparable to understand what Storm Ophelia might do to Ireland.

"Storm Debbie in 1961 was the closest from the point of view of its track. So you would look to Debbie, to see what it did, how it affected Ireland," she said.

Like her colleagues in Met Eireann, she is passionate about her job, the weather and the wonder of using maths and physics to forecast what nature will do next. As she watched the storm approach last Sunday, she realised that Ophelia was doing "exactly what it was forecast to do".

Ophelia unfolded on Monday, more or less as the forecasters had predicted it would. It crashed into Kerry early that morning, a Category Three hurricane downgraded to a post-tropical cyclone with hurricane-force winds that claimed three lives, shut down the country and left hundreds of thousands of people without electricity, water, phones or internet for days.

It razed roofs, felled trees and terrified many of those caught in its violent gusts.

Estimates of the cost of the damage range from €111m to €500m to €800m.

It could have been worse. Widespread flooding didn't materialise. Rain usually stays on the north west of the storm, and winds to south and east. As Ophelia brushed the west coast, most of the rainfall fell in the Atlantic, while the counties of Wexford, Waterford, Cork and Kerry bore the brunt of its winds.

Ophelia was a rare event that has engrossed the scientists and meteorologists at Met Eireann who charted its progress for seven days.

"Normally, off the Cape Verde islands you get clusters of thunderstorms and they go westwards on the trade winds. When they meet the really hot seas in the Caribbean, some of them turn into hurricanes," explained Evelyn Cusack, one of Met Eireann's experienced forecasters.

"But this one actually formed into a hurricane very close to Africa and the Cape Verde islands and went straight up northwards, instead of going westwards. That's the route they normally take."

Ophelia was first noticed as a "tropical depression" on Monday, October 9, was classified as a storm later that day, and a hurricane two days after that. It had changed course, drifting north east, was expected to gather momentum and was soon on course for Ireland. It triggered morning briefings with the US National Hurricane Centre, which tracked its progress, and the Met Office in the UK, which was also in Ophelia's sights. Even the conference calls were unprecedented.

"We all knew it didn't look good," said Liz Walsh, who was, in fact, the only forecaster with Met Eireann who had experienced this type of extreme weather event as a forecaster. She worked for a while for the meteorological service in Wellington, New Zealand. Back working with Met Eireann, Walsh had just returned from an experts' forecasting workshop in the UK. She had learned "new tools for extreme weather forecasting" which she rapidly deployed.

Nasa describes hurricanes as "large, swirling storms" that form over warm ocean waters, "faster than a cheetah" and with winds of at least 119 kilometres per hour, with heavy rain and walls of water pushed in from the sea. They are also warm beasts that need waters of 26 degrees-plus to thrive. As science dictated, Hurricane Ophelia would cool down to a "post-tropical cyclone" by the time it reached Irish shores. But its impact was still going to be huge.

"Because these things are quite volatile, they change very quickly.

"You could have egg on your face if it just decided to go out to sea, which it could have," said Liz Walsh. Forecasters needed certainty. Tracking its course was essential.

The team drew on a range of forecasting models, including European forecasting data and their own short-range Harmonie model.

Forecasters say the different models rarely converge, but for Ophelia, they came worryingly close.

By Saturday morning, Storm Ophelia was on course to hit Ireland within 48 hours. The National Emergency Coordination Group had been triggered the previous day.

People were genuinely worried at this point. "I was starting to lose sleep at this stage," said Liz Walsh. "I was worried about the impact and that if we didn't get the warning out soon enough, people wouldn't take enough notice. This was not the common mid-latitude depression, this was a different beast altogether."

Read More: Crews working 15-hour shifts to restore power post-Storm Ophelia

It fell to another Liz - Liz Gavin - as the forecaster on duty on Saturday morning, to trigger a rarity in Irish weather scenarios, a Status Red alert. It had been on the cards since Friday.

"I was in here early, around 7am. I got up all my charts.

"I was looking at what was happening," she said. Met Eireann has its own Harmonie forecast model, which can read 54 hours ahead and provides high resolution data, and that was coming into play. "The more information we got, the more certainty we were gaining," she said.

Liz was not alone. The team, including Joan Blackburn, the veteran forecaster familiar to many from her RTE weather reports, and Liz Walsh, were among many who clocked in to support her. It was still her decision: "I had to analyse the information and weigh it up, make the call…"

"We cannot let the consequences of a red warning interfere with our line of thinking," said Joan Blackburn. "If we feel the wind or the rain in some cases reach certain criteria, we have to issue it. We cannot be blinkered or affected by what those consequences are."

Liz Gavin issued Status Red for the coastal counties from Cork around to Mayo at midday. The storm was 2,500km away. "We never, ever issue red warnings that far in advance," said Evelyn Cusack. But such were the extraordinary circumstances of Ophelia.

As it travelled, Ophelia intensified to a Category 3 hurricane, but eased back on hitting Ireland's cooler waters.

At 4am Monday, the National Hurricane Centre downgraded Ophelia to a "powerful post-tropical cyclone", but with hurricane-force winds, that was moving north at 70km/h.

The toll of its impact is still being felt this weekend, with lives lost, thousands still without power, and homes ruined.

Meanwhile, Ophelia's less exotic cousin, Storm Brian, was on course to unleash winds, huge waves and rain on Ireland this weekend.

Brian does not share Ophelia's unusual hurricane origins but is capable of huge damage. There were alerts to be issued, advisories to be written.

As they say in Met Eireann, you are only as good as your last forecast.

Sunday Independent

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