Environment Canada has issued a heat warning for most of eastern Ontario, including the Ottawa, Cornwall, Brockville, Kingston, and Belleville regions.
The weather agency says temperatures may rise to close to 31 C Monday afternoon with a humidex of 40.
Overnight lows are expected to reach only around 20 C, which will provide little relief from the heat, Environment Canada says.
Similar levels of heat and humidity are expected Tuesday.
The City of Ottawa said it’s opening two emergency cooling centres at City Hall and the Plant Recreation Centre at 3 p.m. on Monday, with additional sites set to open on Tuesday.
Environment Canada says heat warnings are issued when high temperature or humidity have the potential to pose a risk of heat illnesses, such as heat stroke or heat exhaustion.
Heat illnesses can produce the following symptoms: swelling, rash, cramps, fainting, heat exhaustion, heatstroke and the worsening of some health conditions.
Young children, pregnant women, older adults, people with chronic illnesses and people working or exercising outdoors are at greatest risk when heat waves hit, the weather agency says.
Hot and humid air can also affect air quality.