Toronto has issued its first heat alert of the year as much of southern Ontario is under a humidex advisory.
During a heat alert, people are asked to keep an eye on those who are at risk from heat related illnesses.
Precautions include drinking lots of fluids, staying out of the sun and going to places with air conditioning.
Environment Canada has issued a humidex advisory that stretches from Windsor and Sarnia, around the Golden Horseshoe to Ottawa and Cornwall and as far north as Algonquin and Grey-Bruce.
Humidex values neared 40 over parts of southwestern Ontario on Monday afternoon and the hot and humid air is expected to spread over the rest of the region today.
Temperatures are forecast to reach 32 C or higher and humidex values are likely to exceed 40 in many areas this afternoon. The only respite will be for people living near the Great Lakes where temperatures are expected to be 10 degrees cooler.