Hamilton issued extended heat warning as temperatures climb in southern Ontario

The city's medical officer of health has issued an extended heat warning for Hamilton as temperatures climb through the end of the week.

The hot weather is expected to last from Thursday through Sunday and potentially into early next week, the city said.

Daytime high temperatures will be in the low 30s, it said, with poor overnight cooling around 20 degrees. With the humidex, daytime temperatures will near 40 C. 

Environment Canada's heat warning extends through much of southern Ontario, including Niagara, the Dunnville-Caledonia-Haldimand area, Simcoe-Delhi-Norfolk, Oxford Brant, and Halton. 

The city warns that hot and humid air can also bring deteriorating air quality and can result in the air quality health index to approach the high risk category.

It's reminding the public of its cool places, marked with a "Cool Down Here" sign. Some spray pads have also opened since the city has entered stage two of the province's reopening plan. 

Signs of heat exhaustion, it said, include heavy sweating, weakness, cold, pale and clammy skin, weak pulse, fainting and vomiting. If experiencing symptoms, people should seek help and call 911 if needed. 

Environment Canada warns that the risks of extreme heat are greater for young children, pregnant women, older adults, people with chronic illnesses and people working or exercising outdoors.

It also cautions never to leave people or pets inside a parked vehicle.