Toronto residents are being urged to take precautions as a blast of extreme summer heat blankets the city Thursday and Friday, with dangerously high temperatures and humidex values pushing well into the 40s.Environment Canada has issued a heat warning for the Greater Toronto Area (GTA), warning that a “heat event” is now underway and could stretch into the weekend for some areas.Thursday is expected to be the hottest day, with daytime highs reaching a sweltering 35°C and humidex values soaring up to 44. Clouds will increase in the evening, and Environment Canada is forecasting a 60 per cent chance of showers accompanied by the risk of strong thunderstorms. Overnight temperatures are also expected to remain elevated, with lows between 20°C and 23°C, offering little relief from the heat.On Friday, the mercury will dip slightly but will still be intense, with daytime highs near 30°C and humidex values around 40. The warm overnight trend is expected to continue, with lows near 21°C.While the peak daytime temperatures are forecast to ease slightly heading into the weekend, overnight heat is expected to linger, potentially keeping vulnerable populations at risk.Toronto heat warning raises health concerns as humidex hits 44The city and the surrounding GTA have experienced several hot spells this summer, with humidex values in the 40s. The public is encouraged to stay hydrated, avoid strenuous outdoor activities during peak sun hours, and seek air-conditioned spaces when possible.“Take action to protect yourself and others – extreme heat can affect everyone’s health,” Environment Canada said. “Watch for the early signs of heat exhaustion in yourself and others. Signs may include headache, nausea, dizziness, thirst, dark urine and intense fatigue. Stop your activity and drink water.”Toronto’s extended forecast offers a more promising outlook for relief from intense heat. Daytime highs of 27°C and 25°C are expected, with a mix of sun and clouds on Saturday and Sunday.Click here to sign up for the CityNews Weather Guarantee and to check out Toronto’s extended forecast.