A heat warning has been issued for West Nipissing and North Bay as well as much of Northeastern Ontario.
Environment Canada says the first heat event of the season will bring hot temperatures Sunday into Monday with afternoon highs in the low thirties.
Overnight lows Sunday night are expected to be in the upper teens or low twenties. per teens or low twenties.
The hot temperatures may persist into Tuesday.
According to Environment Canada, hot and humid air can also bring deteriorating air quality which can result in the Air Quality Health Index approaching the high-risk category.
The weather agency says the risks are greater for young children, pregnant women, older adults, people with chronic illnesses and people working or exercising outdoors.
Officials suggest residents watch for the effects of heat illness: swelling, rash, cramps, fainting, heat exhaustion, heatstroke and the worsening of some health conditions.
They say drink plenty of water even before you feel thirsty and stay in a cool place and never leave people or pets inside a parked vehicle.