The scorching temperatures are expected to last until Friday, except for parts of southern Ontario, where they are forecast to linger until Sunday.
The summer solstice was set to arrive Thursday as a heat wave maintained its grip on parts of Eastern Canada for a fourth consecutive day.
The longest day of the year in the Northern Hemisphere will see temperatures hover around 30 to 35 degrees Celsius across parts of Ontario, Quebec and Atlantic Canada, feeling more like 40 with the humidex.
The scorching temperatures are expected to last until Friday, except for parts of southern Ontario, where they are forecast to linger until Sunday.
A pronounced and slow-moving high-pressure ridge has settled over eastern North America, trapping warm air and plunging the region into a stretch of hot and humid conditions. Eastern Canada is on the edge of that high-pressure system, where thunderstorms often form.
Toronto and other parts of southern Ontario were hit with rain showers and thunderstorms overnight. Lanes on the city’s Gardiner Expressway were briefly blocked due to flooding and thousands across Ontario were without power Thursday morning, according to local utilities.
Ottawa and Montreal were among the other cities under risk of thunderstorms.
In Quebec, the province’s health department recommends spending at least two hours a day in an air-conditioned space, having at least one cool shower or bath a day, and limiting physical activity.
Atlantic Canada will also experience similar temperatures smothering most of New Brunswick, Nova Scotia and P.E.I., with central and eastern Newfoundland also under a heat warning.