How Hurricane Fiona became a record-breaking Canadian storm, from the CBC

Warm sea surface temperatures and the storm's track all played a role

Ryan Snoddon · CBC News · Posted: Sep 24, 2023 6:00 AM ADT | Last Updated: September 24

A little over a year ago, on Sept. 14, 2022, Fiona became just another named tropical storm tracking through the Caribbean.

Ten days later, Fiona became one of the most powerful and destructive storms in Canadian history.

Extreme wind gusts of 179 kilometres per hour were recorded at Arisaig, N.S., with widespread, damaging gusts over 130 kilometres per hour clocked across much of eastern Nova Scotia, Prince Edward Island and southwestern Newfoundland

As Fiona rolled in with a huge storm surge and massive waves, a buoy offshore recorded a significant wave height of 17 metres, and a peak wave of 30 metres. That's the length of three school buses.

That wall of water and those significant waves pushed into Cape Breton, the Gulf of St. Lawrence and southwestern Newfoundland with devastating consequences.

Peak winds with post-tropical storm Fiona reached 150 to 180 kilometres per hour. (Ryan Snoddon/CBC)

So how was the storm able to remain so strong as it moved into Atlantic Canada and what made it so destructive? 

While more in-depth scientific studies will be completed over the next few years, here are some of the factors that we already know played a huge role.

Warm sea surface temperatures 

No storm can be directly attributed to climate change, however if you're looking for the most direct link with Fiona, look no further than the ocean. 

Hurricanes fuel themselves in waters over 26.5 C or warmer and sea surface temperatures last summer were well above average, in the high 20s just to our south.

Warmer than normal sea surface temperatures played a key role in Fiona maintaining its strength as it tracked northward. (Ryan Snoddon/CBC)

Unfortunately, Fiona tracked right through the warmest of those waters over the Gulf Stream and the storm was able to retain major Category 3 status until just hours from landfall.

Post-tropical transition

Every hurricane or tropical storm that moves northward into the higher latitudes eventually undergoes post-tropical transformation.

Instead of getting fuel from the water, these storms shift gears and fuel themselves from temperature differences in the atmosphere, the same way everyday low pressure systems and mid-latitude storms do.

In the case of Fiona, the Category 3 hurricane filled with warm air merged perfectly with an incoming cold front just as it began its post-tropical transition.

The large temperature contrasts between the hurricane and the cold front allowed the storm to become an extremely powerful post-tropical storm just as it rolled into Atlantic Canada.

When Fiona made landfall in eastern Nova Scotia it became the lowest pressure ever recorded on land in Canada at 931 millibars. (Ryan Snoddon/CBC)

As Fiona made landfall in Nova Scotia, it set a new record as the lowest pressure ever recorded on land in Canada at 931 millibars.

The Tack

"What if" is a question that comes up a lot after storms roll through.

What if the track was further west or east?

In the case of Fiona, given the size and strength of the storm, there would have been no ideal track.

However, as mentioned above, the path it did take allowed it to remain a hurricane for longer before it became a post-tropical storm.

For P.E.I. and the Northumberland Shore of Nova Scotia, this storm brought the destructive combination of heavy rain, some of the most damaging winds and relentless storm surge.

Many large, historic trees came down in Charlottetown during post-tropical storm Fiona. (Jesara Sinclair/CBC)

My colleague in P.E.I., meteorologist Jay Scotland, says the 60 to 100 millimetres of rain that fell across the island essentially liquefied the rich red soil.

It wasn't just the strength of the winds, but the duration of them that made Fiona so extreme. (Ryan Snoddon/CBC)

The fact that the strongest winds were from the north meant P.E.I. was completely exposed as they howled in from the open Gulf of St. Lawrence.

It was a similar story along the Northumberland Shore of Nova Scotia, where saturated soil and some of the most extreme winds downed thousands of trees and numerous power poles and lines.

As winds gusted well over 100 kilometres per hour for hours on end, trees that didn't break from the wind instead toppled over, as their entire root structures lifted out of the ground.

Remnants of Big Island road in Pictou County, N.S., after Fiona rolled through. (Submitted by Lynn Arsenault)

P.E.I., the Northumberland Shore and also southeastern New Brunswick also took the brunt of the greatest storm surge.

The extreme and relentless northerly winds pushed a massive amount of water from the gulf into the coastlines which caused massive coastal erosion and destruction to infrastructure.

Structures along the coast in Caissie Cape, N.B., sustained heavy damage during post-tropical storm Fiona. (Aniekan Etuhube/CBC)

The track of the storm over Cape Breton aided in the push of storm surge and significant waves into Port aux Basques, N.L., with catastrophic damage.

My colleague in Newfoundland and Labrador, meteorologist Ashley Brauweiler, has been speaking with a few scientists about the impact in Port aux Basques and what happened there.

While only a theory, the consensus is that due to the storm surge and high waves, the water was able to crash and roll over the Channel Head and essentially became trapped. Before the water had time to drain away and escape, yet another wave came crashing in.

The Channel Head at Port aux Basques may have trapped water and added to the high water levels during the storm. (Ryan Snoddon/CBC)

This happened again and again, causing water levels to rise and bringing those massive, destructive waves into shore where they washed away homes.

Between its track, the way the hurricane transitioned to a post-tropical and the warm ocean temperatures that fuelled it, Fiona became a storm for the history books in Atlantic Canada.