Toronto is only halfway through summer and has already surpassed last year’s total number of heat warnings.

The city is currently under a heat warning that started earlier this week, and has been under five warnings so far this year, one more than the total in summer 2024, according to Environment Canada.  

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While it might feel extreme, Warning Preparedness Meteorologist Steven Flisfeder says it’s not entirely out of the ordinary.

“We are seeing more consistently warm temperatures versus last year, but it’s not the warmest summer we’ve had on record,” he told Now Toronto on Wednesday.

The increase in heat warnings is due to a persistent high-pressure pattern over Southern Ontario, which traps warm, humid air and drives up daytime and overnight temperatures. 

These overnight lows are particularly important, as Environment Canada’s criteria for issuing heat warnings include both daytime highs and minimum temperatures that remain elevated through the night.

“This year, we just have a more consistent pattern, allowing for temperatures to get into the low 30’s and remain warm throughout the night as well, which is what we require for our criteria in issuing a heat warning so we’re seeing more high pressure, which allows for the warm, moist air to remain in place over Southern Ontario,” he said. 

So far, the average daytime high for June and July has been 27.8°C, according to data taken from Pearson Airport Flisfeder said. 

“If things don’t change for the rest of the summer, it would be the eighth warmest on record for Toronto,” he added. For comparison, the warmest summer on record was in 1949, with an average daytime high of 28.7°C.

While the city’s current heat warning has been in effect since Sunday, Flisfeder says relief is on the way. 

“Today is expected to be the last day of this heat warning,” he said. 

A cooler air mass is expected to arrive overnight, bringing more seasonal daytime highs of 25°C to 27°C through the weekend.

Urban centres like Toronto are especially vulnerable to prolonged heat events due to what’s known as the “urban heat centre” effect. 

Dense infrastructure, traffic, and concrete surfaces absorb and retain heat, making cities warmer than surrounding rural areas even under the same atmospheric conditions.

Environment Canada urges residents to stay safe during heat warnings by finding access to cool, shaded spaces, ideally with air conditioning, and avoiding strenuous outdoor activity during peak hours.

“If you need to be active, try early mornings or after sunset,” Flisfeder advised. “And make sure you’re drinking lots of water to stay hydrated.”