Summer-like weather has Toronto under a heat warning for the third day in a row as Environment Canada issues an air quality advisory due to the expectation of "elevated pollution levels." 

"Hot and sunny conditions are expected to cause increasing ground-level ozone concentrations this afternoon," the statement read. 

The federal weather agency issued the warnings for Toronto and much of southern Ontario before noon Sunday.

Heat Warning

An ongoing heat wave affecting Toronto has prompted a heat warning for the third day in a row as the humidex makes it feel close to 40 C. (iStock)

The alert advises people of "extreme heat," with the humidex making it feel close to 40 C, and raised health impacts caused by the projected air pollution. 

That means added risks to young children, pregnant women, older adults, people with chronic health conditions and those working outdoors. 

"Individuals may experience symptoms such as increased coughing, throat irritation, headaches or shortness of breath," Environment Canada said, adding those experiencing these symptoms should reduce strenuous outdoor activities until the advisory is lifted.  

Those at risk of suffering heat effects are asked to schedule their outdoor activities during the coolest parts of the day, which include the early morning and evening. 

"Seek a cool place such as a tree-shaded area, swimming pool, shower or bath, or air-conditioned spot like a public building," the statement read. 

"Outdoor workers should take regularly scheduled breaks in a cool place."

The heat warning will likely remain in place on Monday as hot and humid conditions are expected to persist into early this week. 

Heat wave breaks 86-year-old record

Sunday's temperature has already reached a forecasted high of 33 C with the humidex making it feel like 39 C.

A heat warning is issued when very high temperatures or humidity could bring a heightened risk of heat-related illnesses such as heat stroke or exhaustion.

weather dog beach sunglasses Ottawa

Don't forget your sunglasses today: it's going to be hot and sunny in Toronto. (Shutterstock/Zanna Holstova)

Sunday's heat warning is the latest into the season Toronto has seen since 2001. The latest alert the city saw previously came on Sept. 11, 2013.

A ridge of high pressure over the southern half of the province this weekend led to several broken maximum temperature records, according to Environment Canada. 

The ongoing heat wave broke an 86-year-old temperature record yesterday, the weather agency said. 

Toronto saw a high of 30.6 C, compared to a previous record of 29.2 C set in 1931.