Environment Canada has issued a heat warning for Sarnia-Lambton, Windsor-Essex and Chatham-Kent.
The weather agency said maximum temperatures of 30 and 32 Celsius are expected Monday and Tuesday, with overnight lows anticipated to only reach 18 and 21 degrees Celsius.
Humidex values are expected to reach the high 30's to low 40's.
Residents are reminded to drink plenty of water before feeling thirsty and never leave people or pets in a parked vehicle.
"The health risks are greater for older adults, infants and young children, pregnant women, people with physical and/or mental illnesses and people with disabilities or mobility issues," the weather agency said.
Above normal temperatures may last through Wednesday, however, that is dependent on how widespread shower and thunderstorm activity will be on Tuesday.
Cooler temperatures are expected by Wednesday night.