Southern Ontario is preparing for an extended period of hot and increasingly humid weather beginning Monday, with temperatures expected to climb steadily through midweek and remain well above seasonal averages into the Canada Day holiday and the first week of July.
According to weather forecasts from Environment Canada, communities across the Greater Toronto and Hamilton Area, including Toronto, Mississauga, Brampton, Hamilton, Oshawa, Pickering and surrounding regions, are expected to experience a multi-day heatwave from June 29 through at least July 4.
The hot spell will begin on Monday with daytime temperatures reaching approximately 28°C across much of southern Ontario. Increasing humidity will make conditions feel significantly warmer, with humidex values rising into the low 30s. Overnight temperatures are forecast to remain close to 20°C, providing little relief from the heat.
The most intense conditions are expected on Tuesday and Canada Day, when daytime temperatures will climb into the low to mid-30s across much of the region. Brampton and Mississauga could reach highs of around 35°C, while Toronto is expected to experience temperatures near 33°C. Hamilton, Niagara Region, Oshawa and Pickering are also forecast to see temperatures exceeding 32°C, with areas farther inland experiencing the greatest heat.
When humidity is factored in, it is expected to feel closer to 38°C to 40°C in many urban centres. Health experts warn that these conditions pose an increased risk of heat-related illnesses, particularly because overnight temperatures are forecast to remain between 22°C and 24°C, preventing buildings and outdoor environments from cooling adequately.
Canada Day celebrations are expected to take place under hot and humid conditions, with temperatures remaining in the low to mid-30s across much of southern Ontario. Residents planning to attend outdoor events, barbecues, parades or fireworks displays are encouraged to take precautions against heat exhaustion and dehydration.
Weather forecasters also indicate there is a possibility of scattered afternoon and evening showers or thunderstorms on Canada Day. While any storms that develop could produce brief heavy rainfall, gusty winds and small hail, widespread severe weather is not currently anticipated.
The hot weather pattern is expected to continue through Thursday and Friday, with daytime highs remaining between 32°C and 35°C. Although periodic showers and thunderstorms may temporarily cool some areas, they are also likely to increase humidity levels once they pass.
Nighttime temperatures are forecast to remain unusually warm throughout the week, generally ranging between 20°C and 24°C, especially in large urban centres where concrete and buildings retain heat well after sunset.
Health officials are advising residents to stay hydrated, avoid prolonged outdoor activity during the hottest part of the day, and spend time in air-conditioned locations whenever possible. People are also encouraged to check regularly on seniors, young children, individuals with chronic health conditions and neighbours who may be vulnerable to prolonged heat. Authorities continue to remind the public never to leave children or pets unattended in parked vehicles, where temperatures can become life-threatening within minutes.
The prolonged heatwave is expected to remain in place through the Canada Day holiday before temperatures gradually begin returning closer to seasonal levels later in the first week of July.