Environment Canada also issued a heat warning on Thursday, as the federal agency forecast another day of 30 C temperatures.
While the agency predicted the hot and humid conditions to "moderate slightly," the daytime high is still expected to reach 31 C.
By noon, the temperature had reached 28 C under sunny skies. With the humidity, the temperature felt like 31.
Environment Canada issues heat warnings when high temperatures and humidity could lead to an increased risk of heat stroke. The agency is advising residents to visit sick or elderly neighbours, family or friends, and to keep pets out of locked cars.
The city opens seven cooling centres after issuing extreme heat alerts. Click here for a list of centres, including their hours of operation.
Meanwhile, Environment Canada says the heat will stick around on Friday, with a forecast high of 30 C, before temperatures start to cool over Saturday through to Monday. By Tuesday, the daytime high should be a comfortable 23 C.