Summer kicks off with blistering start as heat wave looms over Ontario

People kayak in Lake Ontario near Sir Casimir Gzowski Park in Toronto on Friday, July 6, 2018. THE CANADIAN PRESS/Tijana Martin

TORONTO — Summer in Ontario is getting off to a blistering start with the season's first heat wave looming in the forecast.

Environment Canada says temperatures are expected to top 30 degrees Sunday through at least Tuesday across much of southern and eastern Ontario.

Meteorologist Steven Flisfeder says it could feel more like the upper 30s or low 40s with the humidex.

Monday in Toronto could surpass the daily temperature record by about one degree with the current forecast calling for the mercury to hit a high of 34.

There's no overnight relief in the forecast with temperatures set to stay above 20 through at least Tuesday night.

Studies have shown human-caused climate change, driven by the burning of fossil fuels, is increasing the likelihood and length of Canada's heat waves.

Flisfeder says people should take precautions to stay cool and hydrated ahead of the looming heat and look out for any signs of heat-related illness.

The summer solstice is set for Friday, when the sun will travel its longest path of the year across the sky.

Meteorologists, on the other hand, start the summer clock on June 1 and break the seasons up into consistent three-month blocks to make it easier to collect and compare statistics.

Environment Canada's seasonal forecast says the summer is expected to be hotter and more humid than normal across Ontario.

On Thursday, parts of the Bruce Peninsula through to Parry Sound and North Bay were under rainfall warnings with heavy downpours and possible thunderstorms continuing through the afternoon.

This report by The Canadian Press was first published June 19, 2025.

Jordan Omstead, The Canadian Press