The heat just keeps on coming in Toronto – with another extreme heat alert issued on Wednesday.

Dr. David McKeown, Toronto’s medical officer of health, issued the warning as the mercury is expected to climb to a scorching 33 C.

Environment Canada has also issued a humidex advisory for the Toronto area, warning that the humidity will make temperatures feel like high-30s and low-40s.

Hot and humid conditions are expected to peak on Friday, when a temperate of 35 C is forecast for the afternoon. A cold front is expected to move through southern Ontario on Saturday and flush out the hot and humid air.

During an extreme heat alert, residents are encouraged to call or visit family and friends, especially isolated adults and seniors at a greater risk of heat-related illnesses.

Infants, young children and those with pre-existing or chronic illnesses, the homeless or those who are "marginally housed" are also at risk.

People are also encouraged to stay out of the sun and remain in air conditioned areas and public places, such as shopping malls and libraries.

Wednesday’s extreme heat alert is the third to be declared so far this summer. There have also been six days of heat alerts, including Tuesday.

Toronto’s Medical Officer of Health considers temperature, dew point, humidity, cloud cover, and wind speed and direction when determining whether to declare dangerous weather conditions.

A heat alert is issued whenever the forecast weather conditions suggests a level of mortality between 25 and 50 per cent greater that on a typical day.

An extreme heat alert is issued when the forecast suggests a level of mortality is at least 50 per cent greater than on a typical day.

Following is a list of cooling centres located around the city (address and hours of operation in brackets):

  • Metro Hall (55 John Street, 24 hours)
  • East York Civic Centre (850 Coxwell Avenue, 11 a.m. to 7 p.m.)
  • North York Civic Centre (5100 Yonge Street, 11 a.m. to 7 p.m.)
  • Etobicoke Olympium (590 Rathburn Road, 11 a.m. to 7 p.m.)
  • Centennial Recreation Centre (1967 Ellesmere Road, 11 a.m. to 7 p.m.)
  • Driftwood Community Centre (4401 Jane Street, 11 a.m. to 7 p.m.)
  • McGregor Community Centre (2231 Lawrence Avenue East, 11 a.m. to 7 p.m.)