Some relief from the prolonged heat and humidity is coming for the weekend.
The heat warning, first issued on Canada Day, remained in effect Friday with the air temperature in the low 30s again and the humidex reaching 40 C.
Environment Canada said winds will shift northwest Saturday, bringing in cooler, drier air with a high around 24 C in Sarnia.
There is the chance of severe weather again Friday afternoon in the heat and humidity.
The national weather agency issued a severe thunderstorm watch which was upgraded to a warning at mid-afternoon.
Thunderstorms may be capable of producing strong wind gusts and heavy rain.