WEATHER WARNING: It could feel like 45 C in Toronto and southern Ontario

A dangerous stretch of heat and humidity is sweeping through the region, with a heat warning issued by Environment Canada expected to remain in place through tonight.

The first major heat event of the season is bringing sweltering conditions that could pose serious health risks for residents across southern Ontario.

The warning covers multiple cities in the Greater Toronto Area, including Toronto, Mississauga, Brampton, Vaughan, Markham, Richmond Hill, Oakville, Burlington, Pickering, Ajax, Whitby, and Oshawa. Daytime highs are forecasted to reach 30 to 35 C, with humidex values of 40 to 45 C, creating hazardous conditions for prolonged exposure.

Health officials are urging residents to take steps to stay cool and safe. Everyone is at risk, but seniors, children, individuals with chronic illnesses, and those living alone are especially vulnerable. Authorities recommend checking in on at-risk individuals regularly, either in person or by phone.

Know the signs of heat-related illness:

• Heat exhaustion: headache, nausea, dizziness, dark urine, and extreme fatigue. If these symptoms occur, stop the activity immediately and drink water.
• Heat stroke: red or hot skin, confusion, loss of consciousness. This is a medical emergency—call 911 and try to cool the person with cold water or ice packs while waiting for help.

Additional safety tips include:

• Drink water regularly, even before you feel thirsty.
• Keep your home cool by closing blinds and using fans or air conditioning.
• Spend time in air-conditioned public spaces like cooling centres, libraries, or malls if your home is too warm.
• Avoid outdoor activity during peak heat and wear light, loose-fitting clothing and a hat.
• Never leave children, pets, or anyone in a parked car—check the back seat before locking your vehicle.

Local public health units continue to monitor conditions and advise residents to follow region-specific guidance.