"During a heat alert, the public is encouraged to call or visit family, friends and neighbours, especially isolated adults and seniors who are at greater risk of suffering from heat-related illness, to make sure they are cool and drinking plenty of fluids," said a news release from Dr. Barbara Yaffe, the acting medical officer of health.
"Other groups at risk include people with chronic illnesses, limited mobility and with certain mental health illnesses, infants and young children, people on certain medications and those who are homeless," the release said.
The hottest the city has reached so far this summer is 36.3 C.
On Thursday the temperature is expected to reach 33 C, but with the humidity factored in it could pass that record.
Thursday's alert marks the eighth time this summer the city has issued a heat, or extreme heat alert.