Environment Canada says today might feel like the hottest day of the summer for much of southern Ontario, with temperatures in the mid-30s and humidity making it feel hotter than 40 C.

Environment Canada has issued a humidex advisory for Waterloo and Wellington counties. Cooling centres will be open in Kitchener and Guelph. Outdoor pools in Kitchener and Waterloo are closed for the season.

The hot, humid weather is coming from the U.S. midwest, following a strong warm front.

The high tempeatures and humidity are expected to last until late Wednesday, when a cold front moves through southwestern Ontario.

Early September typically sees highs of 20 and lows of 10 C in Waterloo Region, according to historical data supplied by Environment Canada.