The City of Toronto is under an extreme heat alert on what has become the hottest day of the year.

Temperatures climbed to 32 C in Toronto on Wednesday afternoon, but it felt closer to 40 C with the humidex. Environment Canada forecasted the temperature would spike at 4 p.m. at 34 C, before falling to 27 by 11 p.m. After the sun sets, the weather agency predicts a humidex of 35 C.

The high temperature marked the hottest day in Toronto so far this year, beating Tuesday's record of 31.8 C. The average temperature for this time of year is 25 C.

An extreme heat alert has been issued by the City of Toronto in response to the searing weather. An extreme heat alert is issued when the forecast humidex is higher than 40 C for three days in a row.

During the alert, cooling centres will be open across Toronto from 11 a.m. to 7 p.m. The cooling centres can be found at the East York Civic Centre, North York Civic Centre, Driftwood Community Centre, Etobicoke Civic Centre, McGregor Community Centre, Metro Hall and Centennial Park Community Centre.

Those in the city can also visit air-conditioned shopping malls, libraries and community centres to cool off

Toronto is also under its third consecutive Environment Canada heat warning due to the scorching temperatures. The weather agency said the heat wave is caused by a hot air mass that moved into the region earlier this week and continues to hover over southern Ontario.

Environment Canada's heat warning said some areas may see relief from the heat as early as Thursday, but the agency predicts a high of 30 C, feeling like 33 C, in Toronto. The mass is expected to pass by the weekend, with temperatures forecast to drop to 24 C on Saturday.

Residents of the affected areas are warned to watch for symptoms of heat illness including dizziness and fainting, headache, rapid breathing and decreased urination. Anyone who experiences the symptoms is advised to move to a cool place and drink liquids.

To keep cool during a heat wave, both the city and Environment Canada recommend wearing light-coloured, loose clothing and wide-brimmed hats, and keeping blinds or drapes closed if air conditioning isn't an option.

In addition to Toronto, the following areas fall under Environment Canada's heat warning:

  • Niagara
  • Hamilton
  • Halton-Peel
  • York-Durham
  • Belleville-Quinte-Northumberland
  • Kingston-Prince Edward
  • Stirling-Tweed-South Frontenac
  • Brockville-Leeds and Grenville
  • Ottawa-Gatineau
  • Prescott and Russell
  • Cornwall-Morrisburg
  • Smiths Falls-Lanark-Sharbot Lake