Why a heat warning in P.E.I. may not be a heat warning in Toronto

P.E.I. was under a heat warning for more than half of July, according to Environment Canada. But what's considered a heat warning on P.E.I. may not be considered a heat warning in other parts of Canada.

Heat warnings have different criteria depending on the region, says Environment Canada

Shane Ross · CBC News · Posted: Aug 07, 2018 1:45 PM EDT | Last Updated: August 7, 2018

Heat warnings are issued on P.E.I. when there is maximum temperature of 27 C and a minimum temperature of 18 C for two consecutive days or more, or a humidex of 35 of greater for two days or more. (Submitted by Adam Stewart)

P.E.I. was under a heat warning for more than half of July, according to Environment Canada.

On 18 days, the weather service issued a heat warning for the province. Heat warnings are issued on P.E.I. when "daytime maximum temperatures are expected to reach 27 C or warmer and nighttime minimum temperatures are expected to fall to 18 C or warmer," according to Environment Canada 's website.

Heat warnings on P.E.I. are also issued "when two or more consecutive days of humidex values are expected to reach 35 or higher."

Last month was the third warmest July in Charlottetown in 143 years, according to statistics from Environment Canada.

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Mean temperature of 21.1 C

The mean temperature — the midway point between a day's highest and lowest temperatures — was 21.1 C in Charlottetown. The warmest July in Charlottetown was in 1947, with a mean temperature of 21.5 C.

But what's considered a heat warning on P.E.I. may not be considered a heat warning in other parts of Canada, said Jill Maepea, meteorologist with Environment Canada.

In Toronto, they are more accustomed to having plus-30 degree days whereas in P.E.I. it's not as common so the heat-warning criteria is lower.— Jill Maepea, Environment Canada

"Every province or region has a different criteria across Canada and this was made in conjunction with Health Canada, Environment Canada, and each provincial health agency," she said.

In southern Ontario, for example, heat warnings are issued when there is a high of 31 C and a low of 20 C for two straight days, or a humidex of 40.

P.E.I. heat wave rolls into 2nd week

Returning to normal

Maepea said the heat-warning criteria is based on population habits, and temperatures the public would be used to.

"In Toronto, they are more accustomed to having plus-30 degree days whereas in P.E.I. it's not as common so the heat-warning criteria is lower."

Maepea said normal temperatures are expected to return around the end of the month. Normal mean temperatures on P.E.I. for August are 18.3 C, and 14.1 C for September.

"We're definitely expecting this heat to continue but toward the end of the month they are showing trends of returning to near normal," Maepea said.