A heat warning has been issued for communities such as Ottawa, Gatineau, Kingston and Cornwall as Environment Canada expects a wave of hot, humid temperatures that could last up to a week.

The weather agency issued the alert at late Friday morning for most of eastern Ontario, plus Gatineau and the Grenville-sur-la-Rouge area of western Quebec. No alerts are in place for Renfrew and Prince Edward counties, nor the Bancroft area.

Eastern Ontario and Gatineau's alert said daytime highs are expected to range from 29 to 32 C and with humidity, feel like 35 to 40. Nighttime lows may not dip far below 20 C which means little relief from sweaty conditions.

It's anticipated that Saturday will feel the hottest. Ottawa's forecasted high that day is 31 C and its overnight low Saturday into Sunday is 22 C, plus humidity.

It could be Thursday before it cools off, according to the alert, though forecasts get less certain the further into the future they delve.

The Grenville-sur-la-Rouge area's heat warning may end Monday. The rest of western Quebec has a special weather statement about weather that's expected to be very slightly cooler Friday and Saturday.

Health Canada recommends staying cool and staying hydrated when extreme heat hits, especially for vulnerable people or people with underlying health issues. 

That can mean everything from drinking lots of water and planning outdoor activities for cooler times, to preparing meals that don't require ovens and keeping nearby air-conditioned spaces in mind if needed.

Watch for signs of heat exhaustion — like a headache, dizziness or a rapid heartbeat — and get to a cool place where you can drink water. Heat stroke, which includes confusion and very hot or red skin, is a medical emergency requiring a 911 call.

More resources may be available through your municipality. Ottawa, for example, has a map of public and other places to cool off.