Environment Canada issued Sarnia-Lambton's first heat warning of the summer on Friday.
A hot and humid airmass is expected to remain in place over the region into Saturday with daytime highs in the low 30s and humidex values near 40 C.
By noon Friday, the humidex at Chris Hadfield Airport had already reached 42 C, nearly 108 F.
Overnight low temperatures will be in the low 20s providing little relief from the heat.
The risks are greater for young children, pregnant women, older adults, people with chronic illnesses and people working or exercising outdoors.
Drink plenty of water even before you feel thirsty and stay in a cool place.
Never leave people or pets inside a parked vehicle.
Environment Canada said temperatures Saturday will remain near 30 C (86 F), however, the passage of a cold front will bring cooler temperatures and lower humidity for the rest of the weekend.
