The humidity in the air could make it feel up to 39°C on Sunday.
"Drink plenty of water even before you feel thirsty and stay in a cool place," recommends Environment Canada (EC).
Heat warnings are issued when high temperatures or humid conditions elevate the risks of heat illnesses, like heat stroke or heat exhaustion.
Meanwhile, severe thunderstorms — capable of producing strong wind gusts, large hail and heavy rain — are also expected to hit the metropolis and surrounding areas in the late afternoon on Sunday.
\u201cThunderstorm outlook valid tonight and Monday.\n\nAny report of damage can be sent to Environment and Climate Change Canada by emailing QCstorm@ec.gc.ca or tweeting using #QCstorm.\u201d— ECCC Weather Quebec (@ECCC Weather Quebec) 1658683134
"Strong wind gusts may toss loose objects, damage weak buildings, break branches off trees and overturn large vehicles. Large hail can damage property and cause injury," EC warns.
Yesterday afternoon, severe thunderstorms caused damage from the Outaouais to the North Shore. Hail up to 5 centimetres in diameter were reported over some communities in the Outaouais, the Laurentians and northern Lanaudière.
A tornado even hit Saint-Adolphe-d'Howard in the Laurentians, just over an hour north of Montreal. Strong winds heavily damaged dwellings and broke or uprooted numerous trees.
EC warns that Montreal, Châteauguay, Laval and Longueuil could see comparable conditions overnight.
Severe thunderstorm watches are issued when atmospheric conditions could produce torrential rainfall, damaging winds and sizeable ice pellets.