Environment Canada has upgraded its humidex advisory to a weather warning in light of Thursday's record-breaking temperatures throughout the Greater Toronto Area.

Because of the sweltering weather conditions, severe thunderstorms are possible in Toronto and other southern Ontario communities in the afternoon, Environment Canada said.

If storms develop, the main threats will be damaging winds, large hail and heavy rain, the national weather agency said.

Environment Canada issued the warning as Toronto's temperature is poised to soar to 38 C, setting the stage for what may turn out to be the city's hottest day of the year.

If that's not enough for you, the weather will be even more stifling with the humidity, as humidex values are expected to break the 48 mark.

Weather records eclipsed

Weather records were already falling by 1 p.m.

At 1 p.m., a high of 36.1 C at Pearson International Airport set the all-time high for July 21. Before today, the hottest July 21 temperature ever recorded was 35.6 C, set way back in 1955.

The temperature peaked at 37.9 C at Pearson International Airport, making Thursday the hottest July day on record. The old high of 37.6 C was set on July 7, 1988.

At 5 a.m., it was 26.6 C at Pearson, setting a new record for the warmest minimum temperature.

"Never has it been so warm in the early morning hours in Toronto than it was this morning," said David Phillips, a senior climatologist with Environment Canada.

The previous record, 26.3 C, was set Aug. 1, 2006.

The all-time heat record may fall if the temperature climbs even higher than predicted.

Since record-keeping began, the warmest temperature ever recorded in Toronto was 38.3 C on Aug. 25, 1948.

Environment Canada said the sweltering weather is due to a "heat dome," described as a hot air mass that hovers over a region.

Toronto is going to be stuck in the heat dome for a few more days, with highs of 33 C on Friday and 32 C on Saturday.

Temperatures may return to normal early next week. Normal temperatures for this time of year are highs of 27 C and overnight lows of 17 C.

According to Environment Canada's long-term forecast, there is a chance of rain Saturday, Sunday and Monday.

Extended pool hours

Because of the heat and humidity, the city is urging people to limit their time outdoors and to take precautions to avoid any heat-related problems.

With the city's extreme heat alert in effect, the following public pools are open until 11:45 p.m.:

  • Alex Duff Outdoor Pool, 779 Crawford St.
  • Alexandra Park, 275 Bathurst St.
  • Giovanni Caboto, 1369 St. Clair Ave.
  • McGregor Park, 2231 Lawrence Ave. E.
  • Monarch Park, 115 Felstead Ave.
  • Regent Park Outdoor Pool, 620 Dundas St. E.
  • Smithfield Outdoor Pool, 175 Mount Olive Dr.
  • Sunnyside-Gus Ryder Outdoor Pool, 1755 Lake Shore Blvd.
  • Cummer Park Indoor Pool, 6000 Leslie St.

People can also seek refuge from the heat at the following cooling centres:

  • Metro Hall, 55 John St. (24 hours)
  • East York Civic Centre, 850 Coxwell Ave. (11 a.m. to 7 p.m.)
  • North York Civic Centre, 5100 Yonge St. (11 a.m. to 7 p.m.)
  • Driftwood Community Centre, 4401 Jane St. (11 a.m. to 7 p.m.)
  • Etobicoke Olympium, 590 Rathburn Rd. (11 a.m. to 7 p.m.)
  • McGregor Community Centre, 2231 Lawrence Ave. E. (11 a.m. to 7 p.m.)
  • Centennial Park Community Centre, 1967 Ellesmere Rd. (11 a.m. to 7 p.m.)

Stay safe

In hot, humid conditions, there is a risk of heat stroke and sun stroke.

Here are some tips to keep in mind in times of high heat and humidity:

  • Check on family members, friends and neighbours, especially isolated adults, seniors and people with chronic and pre-existing illnesses.
  • Drink lots of water or natural fruit juices – do not wait to feel thirsty.
  • Go to air-conditioned places, including shopping malls, a library or community centre.
  • Wear loose-fitting, light-coloured clothing made of breathable fabrics.
  • Stay out of the sun.
  • Reduce strenuous physical outdoor activity, especially between 11 a.m. and 4 p.m.
  • Wear sunscreen if you venture outdoors.
  • Landlords of buildings without air conditioning should provide a dedicated cooling room for residents.

People with heart or lung conditions, seniors and children should pay attention to the air quality health index level.

People who need assistance or have heat-related questions are asked to call the Canadian Red Cross' heat information line at 416-480-2615.

Click here for a map of public cooling centres and public places that have air conditioning.

Pet safety

This type of heat can be dangerous for pets, too.

People shouldn't expose their cats or dogs to the heat for extended periods because they could be at risk of heat stroke, according to the Ontario Society for the Prevention of Cruelty to Animals.

Dogs should only be left outdoors for short periods, should have plenty of water and a cool, sheltered place to rest that is out of direct sunlight, the OSPCA said.

Walks should take place in the early morning or evening when it's cooler outside.