Warm or cool? Reversing patterns to dominate Canada in September

Canada’s monthly outlook shows flip-flopping patterns dominating the country throughout September

September is a month of change, and Canada often finds itself caught between the stubborn grips of summertime heat and the slow but steady advance of cooler conditions.

The month ahead will prove no exception to the rule, as many folks across the country will indulge in tastes of both summer and fall through the weeks ahead.

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August 2023 Temp Anomaly

We’re starting September with a long-delayed sizzle across much of Central Canada.

A formidable ridge of high pressure building over the Great Lakes during the long Labour Day weekend will allow temperatures to soar higher than they did in all of August for many communities, exceeding the warmest readings we’ve seen so far this season. Take Winnipeg which reached over 36°C on September 2nd, and Toronto, exceeding 32°C on September 4th, making it the warmest temperature of the year.

Daytime highs will soar into the low-to-mid 30s throughout much of southern and eastern Ontario, with humidex values pushing into the low 40's for communities from Windsor to Moosonee.

National Pattern September

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This burst of summer-like heat is only the beginning of a nationwide pattern that will more closely resemble a see-saw than anything consistent.

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Temp Pattern Early Sept 2023

Forecasters expect above-seasonal temperatures to dominate most of the country east of the Rockies through the first half of the month, arriving in large part courtesy of the same ridge that’ll turn up the heat in Ontario over Labour Day.

Meanwhile, folks along the West Coast will likely see below-seasonal conditions stick around through the first couple of weeks of September.

The pattern reverses for the second half of September

Fans of summer in the eastern half of the country will have to savour the warmth while it lasts, as the atmosphere will play the reverse card and our pattern will flip again heading into the second half of September.

It’s still a couple of weeks away, so the timing is a bit up in the air, but forecasters see signals that warmth will return to Western Canada by the latter half of September.

Temp Pattern Late Sept 2023

Meanwhile, temperatures should tick back toward seasonal for much of Ontario, Quebec, and the Atlantic provinces. Folks across the Far North, especially up by Hudson Bay, may see below-seasonal temperatures as we close out September.

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Remember that ‘seasonal’ changes quickly in September

It’s important to remember as we dive into September that average temperatures change in a hurry as summer fades to autumn.

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Calgary’s seasonal high on September 1 hovers around 20°C before dropping about one degree per week through the month, with a normal high temperature of about 15°C by September 30.

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Down in Toronto, the city’s seasonal high falls from about 24°C on the first of the month to about 18°C by the end of the month.

By and large, temperatures coming in a few degrees above seasonal feels much different in September than it would if the same pattern happened in the heart of the summer.

Watching the tropics

Even as the seasons change over land, we’re entering the peak of the Atlantic hurricane season.

September Tropical Outlook

Water temperatures across the Atlantic have been historically warm this season, fuelling several major hurricanes in rapid succession as we closed out August. The climatological peak of the Atlantic hurricane season occurs during the second week of the month, and strong hurricanes are common throughout September.

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Folks across Eastern Canada will have to keep a close watch on tropical activity in the weeks ahead. No matter how many storms form across the Atlantic, it only takes one storm affecting the area to have a significant impact.

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The best time to prepare for a hurricane is before one even has a chance to form. Use these calm days to take stock of your emergency supplies, ensuring you have enough non-perishable food, water, hygiene products, flashlights, and batteries to comfortably make it through several days without electricity or running water.

Stay tuned to The Weather Network as we look forward to the release of our fall forecast on September 13.

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