Environment Canada has issued a humidex advisory for Toronto and southern Ontario on Saturday, warning that temperatures will feel like they are in the low 40s.
The actual temperature will reach the low to mid-30s C in much of the province's south. The advisory stretches from Windsor to Ottawa, including the Bruce Peninsula and the Niagara region.
Environment Canada says people should stay in air-conditioned or shady areas, limit their activities and drink plenty of water.
An approaching cold front from the north on Sunday will bring relief from the high humidex values, the weather agency said.