Environment Canada has issued a special weather statement, with forecasts calling for between 20 to 40 millimetres of rain to fall in some areas by Tuesday. The rain is expected to begin Monday evening with the most of the rain coming Tuesday.
There's also a risk of thunderstorms on Tuesday.
The culprit is a slow-moving, low-pressure system that will make its way across the Great Lakes region and arrive later in the day on Monday. The system will take a few days to cross southern Ontario.