The forecast is calling for Toronto temperatures to hit 34 C today, with humidity it will feel more like 43 C.
The same story will play out in much of southern and southwestern Ontario, with temperatures set to hit 35 C in Windsor, 34 C in Kitchener-Waterloo and 33 C in London.
A humidex advisory is in effect for Toronto and much of southwestern Ontario.
"I’m already starting to feel the humidity," reported CBC News reporter Linda Ward at 6:30 a.m. ET on Tuesday. "Outdoor pools in the city are already closed so people are advised to drink plenty of water and get into an air-conditioned environment."
Could break temperature records
The Toronto temperature record for Sept. 10 is 34.8 C, set back in 2002. Windsor temperatures would have to hit 35 C today to set a record.
The record for the hottest September day in Toronto is not in jeopardy today. That was set back in 1953 when temperatures hit 37 C.
Things will cool down on Wednesday, where the forecast high in Toronto is 31 C with showers and thunderstorms in the forecast. Temperatures in other southern Ontario cities will see a similar dip on Wednesday.