With less than two week to go before the official start of fall, Toronto and much of southern Ontario could be on track for a last bout of summer storms.

Environment Canada issued a severe thunderstorm watch Wednesday for the GTA and much of southern Ontario.

The agency said an approaching cold front could bring severe thunderstorms, large hail, damaging winds or heavy rainfall. Some areas could potentially see between 50 and 80 millimetres of rain within one to two hours, Environment Canada said in its statement.

The watch, which stretches across southern Ontario, includes Toronto York, Peel, Durham, Hamilton and Halton regions.

The cold front is expected to bring an end to southern Ontario`s last burst of tropical weather for the season.

But before things cool down, the temperature is expected to hit near-record territory with a sweltering afternoon high of 33 C.

With the humidity, it will feel more like 40.

A heat alert and humidex advisory remain in effect.

Since record-keeping began in 1938, the all-time high for Sept. 11 is 33.9 C, a mark set in 1952.

Overnight, a cold front will move through and push the tropical air mass out of the region, giving relief to those who can’t stand the heat and humidity.

However, the cold front is bringing cooler weather over the weekend.

After a high of 24 C and risk of thunderstorms Thursday, Friday will see a high of 15 C and low of 11 C, while Sunday will see a high of 19 C and low of 6 C.

Normal temperatures for this time of year are highs of 21 C and lows of 12 C.

Tuesday's highs eclipsed some records

On Tuesday, the hot spot in Ontario and all of Canada was Sarnia, with a high of 35.9 C, said CP24 meteorologist Chris Potter.

Record highs were set at a handful of weather stations, including Markham (Buttonville), where the temperature reached 35 C. The previous record for that weather station on Sept. 10 was 34.3 C, set in 2002.

The temperature at Pearson airport peaked at 34.1 C, just shy of the record of 34.8 C set in 2002.

Summer officially ends Sept. 22.

So far, the hottest day of the summer at Pearson was July 19, when the temperature hit 34.9 C, Potter said.