A heat warning has been issued for Windsor-Essex and Chatham-Kent.
Environment Canada says temperatures could hit close to 40C with the humidex Sunday.
According to the warning, overnight temperatures will only drop to around 24C with humidity; providing little relief from the heat.
The heat warning will remain in effect Monday with forecasted temperatures remaining around the 40C mark with the humidex.
A cold front is expected to move through southwestern Ontario Tuesday that could bring thunderstorms and milder temperatures, according to the release.