Ottawa and Toronto headed into heat waves early Wednesday, as a third straight day of high temperatures settled in across parts of southern Quebec and Ontario.
"Humidex values in southern Ontario will be between 40 to 45," said CBC meteorologist Jay Scotland, with Ottawa likely having its hottest day of the year — expected to hit the mid-40s.
"North and northeastern Ontario and southern Quebec could experience some severe thunderstorms late in the afternoon and evening."
Scotland said the cool down will move in on Saturday.
"Until then, it's just going to be hot and sticky," said Scotland.
Public health officials are encouraging people to get indoors, get out of heat and into air-conditioned spaces.
The high temperatures pose a particular health risk to the elderly and those who work outside. Humidity makes matters worse, because the moist air impedes the body's ability to cool off by sweating.
- CBC Weather Centre
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People working outside are encouraged to take frequent breaks.
Symptoms of heat-related illness include dizziness, fainting, nausea, vomiting, rapid breathing and heartbeat, extreme thirst, and decreased urination.
Officials are urging anyone caught in the heat to drink lots of water and, if possible, seek relief in a local cooling centre, or even an air-conditioned movie theatre. At least one cooling centre was already open before sunrise in Toronto.
A third straight day of temperatures above 32 degrees means locations like Ottawa and Toronto are officially in heat alerts.
Dr. David McKeown, Toronto's medical officer of health, says the alert will be in effect in Toronto until further notice.
- Read: 7 tips to stay cool in a heat wave
The heat is also sparking high power usage. In southwestern Ontario, many communities hit peak power usage. Guelph Hydro said it expects to break its all-time usage record for the second day in a row on Wednesday.
Usage on Tuesday clocked in at 297 megawatts, according to Guelph Hydro spokesperson Sandy Manners.
"Because it was so hot out, of course everybody was using their air conditioners at full blast and we hit our record demand of 297 megawatts. So, we've never used so much electricity, let's put it that way," she said.