Residents of southern Ontario and Quebec traded in their sunglasses for an umbrella and some rubber boots Tuesday.
The rain started falling heavily in the Greater Toronto Area in the early morning, prompting the Toronto and Region Conservation Authority to issue a water safety message.
Officials say all rivers and streams should be considered dangerous and heavy rainfall will result in higher flows and water levels. Residents are urged to exercise caution around all bodies of water.
As of 8 pm, 33 mm of rain had fallen in Kitchener, and 28 mm had fallen further north in Sudbury. Toronto itself was soaked with about 20 mm of rain.
The rain will continue to push east through Wednesday, with up to 40 mm possible in places like Ottawa and Brockville. Heavier amounts are expected in southern and central Quebec where rainfall warnings have been issued.
Environment Canada says drivers should be prepared for low visibility and difficult driving conditions.
"In addition to the rain, winds will pick up by the afternoon hours and temperatures will drop significantly as well," says Gerald Cheng, a meteorologist at The Weather Network.
The official start to fall is this Saturday. Find out what the season will be like in your area by checking out the 2012 Fall Outlook.