Environment Canada's alert includes Toronto, York-Durham, Halton-Peel and Hamilton regions.
"The unseasonably warm temperatures and humidity are likely to persist into early next week".
In addition to temperatures being well above normal, they'll perhaps even be record-breaking.
In its heat warning, Environment Canada says that residents should do their best to reduce their heat risk by completing outdoor activities during the coolest part of the day and seeking shelter from the sun.
"Really good idea to not do too many strenuous things during the heat of the day, between about noon and 4 p.m.", Coulson advised.
Environment Canada issues heat warnings when very high temperature or humidity conditions are expected to pose an elevated risk of heat illnesses, including heat stroke or heat exhaustion.
Minnesota, Wisconsin among states whose election systems were targeted by hackers
The Department of Homeland Security called Wyman personally to tell her of the activity, he said. Officials are now working to improve voter security in future elections.
The average daytime high for this time of year is 19.7 C.
Temperatures and humidity are expected to increase this weekend under mostly sunny skies.
A return to more seasonal temperatures is expected as we head into the month of October.
We've waited all summer to hear this.
The official start to the fall season began on Friday.
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