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Damage caused by post-tropical storm Fiona at the wharf in Stanley Bridge, PEI, on Sept. 25.Brian McInnis /The Canadian Press

Adam Fenech has spent the past several years thinking about how climate change will affect people across the country, especially in Prince Edward Island where he lives.

Yet, the director of the University of Prince Edward Island’s climate lab said he was still taken aback at how Hurricane Fiona developed into the most severe storm in the province’s history.

“I was not paying any attention to Fiona even a week ago,” said Dr. Fenech, speaking one day after screaming winds and driving rain lashed his house west of Charlottetown while massive trees were uprooted nearby.

“Thank goodness we have the forecasting that we do,” he said. “Without it the tragedies out there would be just monumental.”

East Coast beginning long road to recovery from the devastation post-tropical storm Fiona left behind

One of Fiona’s more unusual aspects is how well it adhered to forecasting models in terms of its trajectory and strength.

For those on the ground, what made the storm so stunning was not a divergence from predictions but what it was like to see those predictions turned into a real-life experience in a place where nothing like it had been seen before.

“You don’t usually get storms that intense,” said Doug Mercer, a meteorologist and forecaster with the Canadian Hurricane Centre in Dartmouth. “So you have to be careful not to underestimate the impact.”

Like other recent global weather disasters, Fiona seemed to cross the boundary between the rare and the hard to believe. In doing so, it has reset the public impression of what kinds of storms are possible in the region.

In this instance, said Mr. Mercer, the storm’s unusual severity was determined by a fateful confluence of conditions, including low wind shear and a path that kept it over the warm waters of the Gulf Stream as it moved north.

As a result, unlike most tropical storms and hurricanes that reach Canada, Fiona lost little of its strength by the time it slammed into a wide swath of the Atlantic coast, centred on a point in Guysborough County Nova Scotia. From there it sped on to the Gulf of St. Lawrence, leaving destruction in its wake.

Lurking in the background is whether the storm is a once-in-a-lifetime fluke or a sign of more to come.

The day after the storm: Stories of resilience as people in Atlantic Canada begin post-Fiona recovery

A similar question arose after a very different weather disaster struck Western Canada last year when the highest temperature recorded anywhere in the country was followed by a wildfire that promptly destroyed Lytton, B.C., the place where the record was set.

An analysis conducted after the catastrophic fire showed that the temperature spike was so unlikely it should be expected to occur only once in a thousand years. But that would be without taking into account the effects of climate change, including a shift to a warmer and drier Pacific Northwest, as documented in a 2019 federal report. That would significantly increase the chance of record-setting temperatures.

In Fiona’s case, the key variable was the record low air pressure where the eye of the storm hit land. Exactly how low is somewhat uncertain as there was no weather station directly on the storm’s centreline. However, based on measurements near the line, meteorologists at the hurricane centre estimate that such a station would have recorded a pressure as low as 931 millibars as Fiona passed through.

This is what drove the storm to be so intense. The speed of the wind around a tropical storm or hurricane is a function of the lack of air pressure that the wind is spiralling into. One station, at Arisaig, N.S., recorded a peak wind speed of 187 kilometres per hour at the height of the storm.

The counterclockwise direction of the winds drove powerful storm surges onto the coast. East of the storm’s track, those surges came from the south and were especially pronounced in Channel-Port aux Basques, N.L., where waves “were coming in over 12 metres and probably breaking over 16 metres,” Mr. Mercer said.

It was here that a 73-year-old woman died after her home was hit by the surge and she was swept out to sea, according to the RCMP.

On the opposite side of the storm track, winds from the north battered PEI’s north coast and caused extensive flooding. For example, instruments show that at Red Head Harbour, a sheltered wharf that is typically more than 1.5 metres above sea level, measured 70 centimetres below sea level early Saturday morning.

In a special report on oceans produced in 2019, the UN Intergovernmental Panel on Climate Change made clear that the first and most pronounced effect of climate change for many living in coastal regions would not be the gradual rise in average sea level around the globe, but the increasing likelihood of high-water events as a consequence of sea-level rise.

In parts of Atlantic Canada, high-water events that occurred on average about once per century in the recent past could come to be annual events by the 2060s, according to climate projections. That means if Fiona is the outlier today, it is unlikely to stay that way.

Precisely how much of Fiona’s impact can be attributed to climate change has yet to be determined, Dr. Fenech said. That will have to wait until he and other researchers can run detailed computer simulations of the storm using the same initial conditions and seeing what happens with and without the presence of warming linked to greenhouse gas emissions.

But previous work already suggests climate change is having an effect on tropical systems that enter Canadian waters.

In one study published last year in the journal Earth’s Future, researchers studied 35,000 simulated tropical cyclones with tracks that came within 250 kilometres of the city of New York. Although the focus of the study was the U.S. northeast, the results have implications for Canada.

“One thing we did find … was that more tropical cyclones tend to last both farther north and east in the Atlantic basin in a warmer climate,” said Andra Garner, an associate professor at Rowan University in New Jersey, who led the study.

The key factor that connects the result to climate change is the presence of warmer ocean waters that allow strong storms to persist into more northerly latitudes than has historically been the case, she added.

If so, rising global temperatures are likely to send more powerful hurricanes and post-tropical storms Canada’s way.

“It’s only going to get warmer,” Dr. Fenech said. “I’m not happy to say it, but we should get used to this.”