"Exceptionally hot and humid conditions" are expected in Toronto on Wednesday, with humidex values making it feel like nearly 43 C outside, Environment Canada says.
The forecast calls for daytime high temperatures of 31 to 33 C and humidex values of 42 to 43, the federal weather agency says.
A special weather statement is currently in effect for the city.
Overnight low temperatures on Wednesday, forecast to be 21 to 23 C, will provide little relief from the heat, it adds.
No heat warning to be issued for Toronto
The federal weather agency says it will not issue a heat warning because daytime high temperatures are not expected to reach the threshold of a warning on Thursday due to the passage of a cold front.
Heat warnings require hot and humid conditions to last for two days, with daytime temperatures of 31 C or humidex values of 40, as well as overnight lows of 20 C or higher in between those two days, it says.
Air quality can deteriorate due to the hot and humid air and the air quality health index can approach the high risk category, it says.
Beating the heat
To stay safe in the heat, the weather agency advises the following:
Drink plenty of water before you feel thirsty and stay in a cool place.
Check on older family, friends and neighbours to make sure they are cool and drinking water.
Never leave people or pets inside a parked vehicle.
Keep homes cool and block the sun by closing curtains and blinds.
Outdoor workers should take regularly scheduled breaks in a cool place.