Environment Canada says temperatures are slightly higher than normal.
Much of southern Ontario has been under a heat-event over the weekend with highs in the 30 degree mark and humidex values near 40 degrees Celsius.
Meteorologist Kristina Kretchman said temperatures will start cooling down Monday evening.
"A slow moving cold front will be moving across the area beginning later [Monday] and that will bring an end to the heat event for areas in central Ontario and the northern parts of southwestern Ontario," she said. "For the rest of southern Ontario it's going to be hot and humid conditions heat warning conditions through Tuesday."
Kretchman said for the rest of the province Wednesday is when temperatures will start to cool down before higher temperatures creep in again.
"Some guidance suggests there could be a return to these hot and humid conditions beginning possibly Friday or more likely Saturday," she said.
This multi-day heat event is because of a ridge of high pressure.
Kretchman said this has caused temperatures to be higher than normal.
"Daytime highs are normally 25 degrees Celsius and overnight lows 15 degrees Celsius, but at this point with the heat event ongoing we have forecasted highs anywhere between 30 to 35 degrees Celsius," she said.
Environment Canada reminds residents when it is hot and humid outside to drink plenty of water, stay in cool, air conditioned places and to wear loose, light-fitted clothing.
We're also reminded to watch for signs of heat exhaustions. Signs include headache, nausea, dizziness, thirst, dark urine and intense fatigue.