Much of southern Ontario, including London-Middlesex, Chatham-Kent, Windsor-Essex and Sarnia-Lambton, has been put under a heat warning from Environment Canada.
The warning calls for daytime highs in the low 30's C on Monday, with maximum humidex values near 40 C.
Overnight temperatures are only expected to fall to about 20 C.
The weather agency is advising residents to drink plenty of water before you feel thirsty to decrease your risk of dehydration.
Heat warnings are issued when very high temperature or humidity conditions are expected to pose an elevated risk of heat illnesses, such as heat stroke or heat exhaustion.
