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Here’s everything you need to know about the heat wave in Toronto

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Environment Canada suggests temperatures could soar between 30 to 36 C. Here's a look at how the city is responding and how residents are reacting

Environment Canada’s heat warning has officially settled in as experts warn “dangerously hot and humid conditions” will grip much of the GTA this afternoon heading into Tuesday night.

As of 5:43 a.m., the alert now suggests temperatures could reach 30 to 36 C, with humidex values between 40 and 45 and overnight lows of 21 to 25 C “providing little relief.”

“You can’t escape it. It’s there,” Environment Canada’s senior climatologist, Dave Phillips told CP24.

“We haven’t had a lot of rain in June, but we had a lot last Wednesday and a couple of hours yesterday. All this water is now being evaporated by the heat and it’s creating this kind of oppressive humidex.”

‘Dog days’ still ahead, Phillips warns

Phillips warned that this wave will feel especially harsh because of its timing and intensity. “This is jungle air coming northward. We’re going to add our own humidity to it from the rains we had over the last few days and it’s going to be very oppressive and really unhealthy,” he said.

“We call it dangerous. You know, we don’t use that word very often but it’s dangerous because it’s the first one of the season, and we’re not used to it.”

While temperatures could approach 35 C on Monday — a mark not reached in Toronto for two years — Phillips suggests the early-season heat is only just the beginning of what’s to come.

“This is the warmest day we’ve had in two years, and the dog days of summer are still a month away,” he said.

“We may not see a warmer moment than 35 degrees, as we’re forecasting tomorrow... but it’s going to be here and there’s no escaping it.”

The veteran climatologist also emphasized the serious health impacts that accompany such conditions. “They call heat the silent killer. People aren’t going to be dropping to the streets in Toronto, but it’s going to affect people, particularly with pre‑existing conditions, who are living alone and don’t have the ventilation,” he said.

“More people die from heat in the world than any other element. You can be fit and athletic, and even those people can suffer under these extreme heat conditions.”

Symptoms of heat related illness?

Today’s warning also marks the “first significant heat event of the season” and officials are warning residents to watch for signs of heat-related illness, including “headache, nausea, dizziness, thirst, dark urine and intense fatigue.”

Forehead sweat on man stock photo A stock photo of a man with perspiration visible on his forehead. (pexels.com/cottonbro studio)

The agency emphasizes that “heat stroke is a medical emergency” and instructs residents to call 911 if someone shows signs such as “red and hot skin, dizziness, nausea, confusion and change in consciousness.”

“While you wait for medical attention, try to cool the person by moving them to a cool place, removing extra clothing, applying cold water or ice packs around the body,” the agency said.

“Drink water often and before you feel thirsty to replace fluids. Close blinds, or shades and open windows if outside is cooler than inside. Turn on air conditioning, use a fan, or move to a cooler area of your living space. If your living space is hot, move to a cool public space such as a cooling centre, community centre, library or shaded park.”

Over 500 cooling spaces open

On Saturday, Mayor Olivia Chow revealed that the city has opened over 500 cooling spaces across the region.

Olivia chow Mayor Olivia Chow speaks to reporters on Saturday June 21, 2025 (CP24 photo).

The spaces include libraries, community centres and senior homes, Chow said.

In addition, city staff will be going door‑to‑door doing wellness checks on vulnerable residents in partnership with the Red Cross.

The following six air-conditioned civic buildings are also open to the public while the heat warning is in effect:

  • Metro Hall
  • Scarborough Civic Centre
  • Etobicoke Civic Centre
  • York Civic Centre
  • East York Civic Centre
  • North York Civic Centre

Additional information, including tips for beating the heat, can be found on both City of Toronto and Environment Canada websites.