Heavy rain has twice this month caused flash flooding and commuter chaos in the city, and Toronto is preparing for the chance it may have to do it all over again.

Environment Canada is calling for anywhere from 15 to 25 millimetres of rain Tuesday, with showers forecast to start early and thunderstorms predicted for much of the afternoon and evening.

“We do certainly have to monitor how it unfolds, because as we’ve grown to know, thunderstorms can give a lot of rain in a short span of time,” Environment Canada meteorologist Gerald Cheng told the Star. “We see a lot of moisture coming.”

Senior Environment Canada climatologist David Phillips warned “it has potential for being a memorable storm,” adding that a lot can change before the rain hits. “24 hours is a huge amount of time in weather.”

Monday night, Environment Canada issued a special weather statement for Toronto and much of southern Ontario, as Tuesday holds the potential for heavy rainfall.

A few periodic rounds of showers and thunderstorms are expected on Tuesday, with many areas receiving anywhere up to 20 to 40 millimetres of rain by Tuesday evening. Areas that get several thunderstorms may receive significantly higher amounts of rainfall, however.

On Friday evening, heavy rain shut down service on the TTC’s Line 3 and flooded parts of Union Station.

The station will be equipped with additional staff on Tuesday to prepare for the weather, the City of Toronto said in an email to the Star.

“The safety of all those who work, visit or commute at Union Station is the top priority of the City of Toronto,” the statement read.

“Following the recent floods, City staff have also proactively taken steps to reduce future flooding at the station, including repairing a track drain in the York teamway.”

Metrolinx spokesperson Anne Marie Aikins said the station’s teamways — the walkways adjacent to the York and Bay St. underpasses — are often the first to flood in heavy rainfall.

“We know there is a lot of rain coming tomorrow. It is coming over a longer period of time, and that’s better news for infrastructure,” Aikins said.

Metrolinx is advising customers should give themselves more travel time than usual.

Read more: Everything you need to know to prepare for Toronto’s next flash flood

What do you think?

According to Cheng, the city has seen 143.8 millimetres of rain so far this August, recorded in the vicinity of Billy Bishop Airport. Toronto’s record for rain in August is the 206.8 millimetres that fell near the University of Toronto in 1915.

A single storm that year dumped 109 millimetres of rain in the city, damaged nearby crop fields and killed five in a car crash north of Gravenhurst, according to Environment Canada.

Loading... Loading... Loading... Loading... Loading... Loading...

Toronto’s most vicious storm this year swept over the city late on Aug. 7, bringing a torrential downpour and as much as 100 millimetres of rain in some areas, according to Environment Canada.

That same night, the agency said more than 64 millimetres of rain fell in only two hours at Billy Bishop Airport.

“After that unbelievable heat wave that we saw at the beginning of this summer, I believe we are finally catching up,” Cheng said.

Claire Floody is a breaking news reporter, working out of the Star’s radio room in Toronto. Follow her on Twitter: @claire_floody

Read more about: