The Greater Toronto Area is expected to experience a significant "heat event," with temperatures rising to around 40 degrees Celsius along with increased humidity.

The Canadian Ministry of the Environment stated in a weather announcement that a change in temperatures is expected to begin today, Sunday, and will last between three to five days, noting that “a hot air mass is expected to affect the region starting Sunday and continuing until Wednesday.”

Although nighttime temperatures are below warning thresholds in some areas, the humidity and daytime highs will be quite unusual during early September.

The weather agency warned that high humidity could lead to a deterioration in air quality, with temperatures expected to reach around 30 degrees Celsius, or between 35 and 40 degrees Celsius with humidity.

The Canadian Environmental Agency advises residents to stay hydrated, drink fluids, and check on vulnerable family members and friends.

The sudden heatwave is likely to be a shock to the city, which has not experienced temperatures above 30 degrees Celsius throughout the month of August.

David Phillips, Chief Climatologist at the Canadian Ministry of Environment and Climate Change, told CTV News on Thursday, "We usually see about four or five of those days in August, and we’ve had nothing; the weather has definitely been cool and humid, with nearly half of this summer's days being rainy."

Phillips added that Toronto has experienced temperatures exceeding 30 degrees Celsius only eight times throughout the summer, with the last time the temperature in Toronto surpassed 30 degrees Celsius being on July 28 (31.2 degrees Celsius).