A heat warning remains in effect in Barrie, Collingwood, Hillsdale, Midland, Coldwater, Orr Lake, Orillia, Lagoon City and Washago.
Daytime high temperatures that are more than 30 C are expected, with humidex values predicted to be in the high 30s to low 40s.
Overnight lows are expected to be near 20 C, providing a little bit of relief from the heat.
Environment Canada says a “slightly cooler air mass” may move into the area on the weekend, but whether this will happen is still unclear.
The federal weather agency says hot and humid air can bring “deteriorating air quality,” which can result in the air quality health index approaching the “high risk” category.
“The risks are greater for young children, pregnant women, older adults, people with chronic illnesses and people working or exercising outdoors,” Environment Canada says, adding that people or pets shouldn’t be left inside a parked vehicle during the heat.