Environment Canada has issued a heat warning for parts of southern Quebec, including Montreal Island and Laval.
Humidex values will reach and could even "slightly exceed" 40 between Monday and Tuesday.
Humidex value between Monday and Tuesday
Rain on Tuesday night will finally cut the heat, Environment Canada forecasts.
The agency advises residents living in regions under the heat warning, which include the South Shore, Eastern Townships, and part of Lanaudière, to "drink plenty of water even before you feel thirsty" and "stay in a cool place."
The Weather Network forecasts temperatures in the mid to upper 20s C for the rest of the week.