A heat warning issued by Environment Canada for Guelph, Waterloo Region and Wellington County could continue into the middle of the week.
The agency says to expect daytime highs of between 30 C and 32 C, which could feel like 37 to 40 with the humidex values.
There won’t be much respite at night as the temperature is only expected to fall to 21 C.
Environment Canada warns that the hot, humid air can cause the air quality to deteriorate, causing the Air Quality Health Index to approach the high-risk category.
While extreme heat affects everybody, the agency says it is riskier for young children, pregnant women, older adults, people with chronic illnesses and people working or exercising outdoors.
Some signs of heat illness to watch for include heat illness: swelling, rash, cramps, fainting, heat exhaustion, heat stroke and the worsening of some health conditions.
Environment Canada says to never leave any living creatures inside a parked car.
It says it issues heat warnings when high temperatures or humidity conditions are likely to create a higher risk of heat illnesses like heat stroke or heat exhaustion.