Environment Canada has heat warnings in place for all of western Quebec and most of eastern Ontario Thursday and Friday.
On the Ontario side of the Ottawa River, it may linger into the long weekend.
People could see daytime temperatures reach 32 C, with humidex values near 40, Environment Canada said. Nighttime lows could stay above 20 C.
There are no warnings for more westerly parts of eastern Ontario such as Renfrew, Sharbot Lake and Kingston.
In Ottawa the 10 a.m. temperature reading at the international airport Thursday was already 26.5 C, the average high for Aug. 1. Humidity made it feel like 36 then, should peak at 39 and make it feel like 27 overnight into Friday.
Friday should have a similar high, then Saturday’s high is 28 C.
July was Ottawa’s eighth straight month with an average temperature higher than the standard set in the 1980s, 90s and 2000s.
Extreme heat can pose significant health risks to everyone, but certain groups are particularly vulnerable. These include older adults, infants and young children, pregnant people and those with physical or mental health conditions.
Ottawa Public Health offers an interactive map of places to stay cool throughout the city, including pools, libraries, splash pads and community centres, plus fountains. Other health authorities and municipalities have shared similar maps.
Everyone is being asked to avoid exercising during peak heat times, staying inside where possible — especially in spaces that are being cooled — and drinking plenty of fluids.