"We are looking at very muggy, very warm conditions for much of the eastern half of the country," CBC meteorologist Jay Scotland said early Tuesday.
Southern and eastern Ontario and southern Quebec will have humidex values around and in excess of 40, Scotland said, with slightly cooler but still hot and muggy weather in parts of New Brunswick and southern Nova Scotia.
Montreal, Toronto and Ottawa are expected to see highs of 31 C, 33 C and 34 C, respectively, with temperatures feeling over 40 with the humidex.
Toronto's Medical Officer of Health upgraded the heat alert started Monday to an extreme heat alert.
"During an Extreme Heat Alert, call or visit family, friends and neighbours, especially isolated adults and seniors who are at greater risk of suffering from heat-related illness, to make sure they are okay," the city advises.
Given the humid conditions, pop-up thunderstorms are possible in both Quebec and Ontario, Scotland said.
In the Maritimes, temperatures will go down slightly compared with Monday when temperatures ranged from the low to high mid-30s, including 36 C in Bathurst.
"Northern New Brunswick will see temps back down into the 20s today, but the southwest is still warm, with highs into the low 30's," Scotland said, adding that Nova Scotia is also be warm today with Halifax hitting 29 C.
Environment Canada expects the heat and humidity in eastern Canada to break Thursday or Friday, depending on the area.
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