A heat warning is in effect as Toronto and most of the GTA are set to experience some of the hottest temperatures of the year.

Environment Canada says starting Monday, daytime highs are expected to reach 31 C and coupled with the humidity, it will feel somewhere between 35 to 38.

“During this heat event there’s going to be very little in the way of relief through the overnight as lows are expected to hover close to 20 C,” CityNews meteorologist Jessie Uppal says.

“We’re not expecting much cooler or fresher air until late Tuesday night, if not Wednesday, where we do have a low-pressure system tracking through bringing more cloud cover and some steady rainfall by the middle of this week.”

The warning is also extended to Burlington, Oakville, Hamilton, Mississauga, Brampton, Vaughan, Richmond Hill and Markham.

The warm, humid temperatures present health risks for older adults, infants and young children, pregnant people, people with physical and/or mental illnesses, and people with disabilities or mobility issues.

Symptoms of heat illness include swelling, rash, cramps, fainting, exhaustion and heat stroke.

“Drink plenty of water regularly, even before you feel thirsty to decrease your risk of dehydration,” Environment Canada warned. “Never leave people, particularly children, or pets inside a parked vehicle.”