Summer lingers as warmth wins out across Canada in September
Expect a gentler-than-normal slide from summer into autumn across the country as a generally warmer pattern prevails
September is typically a month of rambunctious transition across Canada as summer’s iron grip fades against doses of increasingly chilly autumn air.
But even as our seasonal temperatures steadily slide through September, our month ahead looks to feature a spell of extended late-summer weather across much of the country.
We’ll still have to watch a few wildcards, though, that may throw a wrench into the upcoming patterns.
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September starts with major heat south of the border
A major and unusual heat dome building across the U.S. will influence conditions across much of southern Canada to kick off September. Some areas south of the border will experience mid-summer heat as we begin climatological autumn.
While the bulk of the heat will remain to the south, the ridge responsible for this late-season heat will nudge above-seasonal values into parts of Canada. Communities like Windsor, Ont., are on track to start the month with daytime high temperatures as warm as the mid-30s.
Forecasters will also have to closely monitor clusters of thunderstorms that will track along the periphery of the ridge. These organized clusters would be capable of producing severe weather, including gusty winds and heavy rainfall.
Temperatures should run warm for most of Canada
Thanks in part to that general ridging pattern that will dominate much of North America, September as a whole will come in above-seasonal across most of Canada east of the Rocky Mountains.
We’ll see the focus of the warmth shift east and then back west at times throughout the month, and chilly air will occasionally push south--especially across Eastern Canada. But for most communities, temperatures through the month should generally run warmer than normal.
It’s important to note that seasonal temperatures steadily drop through the month of September, so an “above-seasonal” day can remain quite pleasant compared to a similar setup in the middle of July.
That said, conditions across Canada will feel like late summer more often than it will feel like early autumn.
Watching Atlantic hurricanes and Pacific typhoons
A major wildcard for September’s outlook is the potential for typhoons recurving out of the western Pacific basin. The tropics remain very active across the Pacific thanks to a fast-growing El Niño in the region.
The remnants of typhoons racing north can inject instability into the jet stream that could disrupt the upper-level pattern downwind over Canada. Such a disruption can lead to ridges bringing above-seasonal warmth to Western Canada while chilly troughs dip over the eastern half of the country.
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Folks along the neighbouring Atlantic coastlines will closely watch the tropics as we approach the peak of Atlantic hurricane season. Those same El Niño conditions are leading to well below-average activity in the Atlantic.
Coastal residents cannot let their guards down despite the quiet pattern. Disruptive tropical systems can and sometimes do slip through a generally unfavourable setup, and warm waters may create a risk for storms forming closer to home.