TORONTO -- Most communities in Ontario and Quebec remained under heat warnings Thursday as forecasts showed no signs of a significant cooldown on the horizon.

"There's no relief in sight. It's just sitting around like an unwanted house guest, and won't leave," Environment and Climate Change Canada senior climatologist David Phillips told CTV News Channel on Thursday from his home in Barrie, Ont.

Phillips said heat warnings were in effect for more than 70 districts in the two provinces, including the heavily populated areas around Toronto, Ottawa and Montreal, in what could be the hottest stretch of weather any of these regions will experience this year.

"This is really relentless," he said.

"Even in the shade, where we measure temperatures, it just seems unbearable."

The nation's capital reached 29 C before 10 a.m. Thursday and had a projected high of 34 C, which would make it the ninth straight day the mercury had gone over 30 C in the city. Phillips said he can find no record of Ottawa having ever before experienced a heat wave of this length.

In Toronto, where most weather-related attention was on the sudden but severe storm that moved through the city Wednesday afternoon, Thursday was expected to be the eighth straight day the mercury soared past 30 C.

Forecasts for Montreal called for highs of 36 C on Thursday and Friday. If that happened, it would mark the two hottest days thus far this year in the city. Friday was also forecasted to be the warmest day of the year in Ottawa, with a projected high of 35 C.

With the humidex factored in, conditions in many areas covered by the heat warnings could feel more like the mid-40s on Thursday and Friday, Phillips said.

Forecasts show an upcoming slight dip in temperatures in southern Ontario and Quebec, with daily highs between 27 C and 30 C from Saturday through Monday.

After that, though, it is expected that conditions will once again heat past 30 C.

"It's like summer reruns all over again – just day after day," Phillips said.

"Get used to it."

The early-July heat is not nearly as extreme in the rest of the country, although one community did set a daily record for hot weather on Wednesday. Nain, N.L. sweltered through its warmest known July 8, with the temperature hitting 26.3 C – more than a full degree above the previous record, which was set in 2010.

Environment and Climate Change Canada warns that anyone in an area that is experiencing extreme heat should stay hydrated and out of the sun as much as possible, close curtains and blinds to keep their homes cool, and check on at-risk neighbours and loved ones.