Brothers Mohammed, centre, Yousef, left, and Abdullrahman Othman try to cool off while playing in the water fountains at Dundas Square in Toronto on Monday. (Darren Calabrese/Canadian Press)

The heat wave that is scorching Toronto isn't particularly unusual, but it is breaking records when it comes to nighttime temperatures, says a senior meteorologist.

Dave Phillips, senior climatologist for Environment Canada, said "our memories are quite short when it comes to weather. We tend to think that what we're in the midst of no one's ever experienced that before."

Disregarding the last two summers, which were unusually cold and wet, heat waves like this week's are to be expected, he said.

Toronto has been under an extreme heat alert since Monday as temperatures hit the low- to mid-30 C range across southern Ontario and Quebec. With the humidity, it will feel closer to the mid-40s.

This particular heat wave will probably last for another two or three days, and so far, no maximum temperature records have been broken, said Phillips.

But the nighttime temperatures recorded in the past few days have been very high, he said.

New records

For instance, Tuesday's minimum temperature in Toronto was 23.3 C, a new high. The normal minimum temperature during this time of year is 16 C.

"These are new records. It has never been so warm in the city on these particular days in the past," said Phillips.

"Some of the big heat waves in the world, it has been the nighttime temperatures failing to drop down low that create the health problems."

Compared to the same time last year, emergencies related to breathing problems are up by 58 per cent, according to Paul Raftis, deputy director of operations with Toronto EMS. Fainting as a result of the heat is up 51 per cent, he said.

The city is trying to do its part to shelter its citizens from the heat. Seven cooling centres are open around the city until 7 p.m., while a cooling centre at Metro Hall in downtown Toronto is open 24 hours.