Environment Canada has issued a heat warning for Sarnia-Lambton.
The federal weather agency says the maximum temperature Sunday and Monday will reach 31 C with the humidex reaching 40 C both days.
Minimum temperatures Sunday evening will range between 20 to 23 C providing little relief.
To reduce the risk of heat-related illness, the weather agency advises the public to take precautions while outdoors by scheduling activities during the cooler parts of the day, to take breaks in a cool place while working outside, and to drink plenty of water before feeling thirsty.
Environment Canada has issued a rainfall warning for Watford, Pinery Provincial Park and eastern Lambton County.
Rain, at times heavy, is expected Sunday morning.