Heavy rain, thunderstorms in the forecast as Toronto remains under rainfall warning

People carry umbrellas while walking during a downpour of rain in Toronto on Tuesday, Sept. 27, 2022. THE CANADIAN PRESS/Alex Lupul

Toronto has already seen a month's worth of rain in the last three days and is expected to see more precipitation over the next several hours, an Environment Canada senior climatologist said on Tuesday.

A rainfall warning is in effect for the city and many other regions across southern Ontario, with Environment Canada calling for up to 50 millimetres of rain.

"We've had a month's worth of rain in two days in September, and that same active weather system is still in play and is going to bring a weather system into the area," Dave Phillips told CP24 on Tuesday afternoon.

He said the region would see steady showers begin mid-afternoon before heavy rain arrives in the evening.

"The rain's going to get heavier and carry on right through to midnight, and then sometime around midnight or shortly after, you're going to actually not just hear the raindrops on your window, you're going to hear thunderboomers. You're going to have some thunderstorms, see lightning and heavier rains will follow that," Phillips said.

He noted that the rain is expected to taper off around noon Wednesday.

According to Phillips, Toronto saw 75 to 76 millimetres of rain between Saturday and Monday. He said yesterday was the wettest Sept. 23 on record in the city.

Toronto usually gets 69 millimetres of precipitation for the whole month of September.

"With all that rain we're going to see, river courses are going to become more swollen. So, people have to stay away from river courses, and we're going to see ponding and pooling," Phillips said.

He added that flash flooding is also a risk.

"We know what that does to Toronto with so much asphalt pavement and building material. There's no green space to soak up that rain and so it's going to be a quick runoff, and that rain is going to create submerged underpasses and maybe lead to some flooded basements," Phillips said.

"So, hey, we know that it doesn't matter how dry Toronto is, a raindrop becomes a flood drop, and so another rain event is going to add to the expense and the misery in the Toronto area."

After experiencing one of the wettest summers on record, Toronto saw a particularly long stretch of dry conditions earlier this month. Those dry conditions ended abruptly this week as more wet weather arrived.

"We had so many records that we broke in summer: the wettest summer, the wettest months, the wettest day. And then we got the faucet got turned off in the first three weeks of September. We had barely any rain," Phillips said.

"Then all of a sudden, on Saturday, we had some active weather systems set up in the Great Lakes area. A lot of weather systems in the United States coming in."

Phillips said dry conditions will follow the rain event with a 30 per cent chance of showers for the last two days of the month.

Sunshine and mild temperatures are expected to return later this week, and a brighter weekend is on tap for the city.