Heavy rainfall and high winds in Toronto and much of southern Ontario prompted Environment Canada to issue a special weather statement Monday.
The warning was for a large area stretching from Windsor to Ottawa.
Environment Canada forecast between 15 and 20 millimetres of rain for Toronto on Monday, down from an earlier prediction of between 15 and 25 millimetres.
Much of the rain is expected to fall in the afternoon. If it nears the maximum forecast, the rain would break the Toronto precipitation record for April 4, set in 1968, when 18 millimetres fell.
On Monday, gusts of between 40 and 60 kilometres an hour are expected, along with a high of 16 C, well over the seasonal average high of 9 C. But the mild weather will come to an end late Monday as an incoming cold front brings temperatures to around the freezing mark, the forecast said.
Environment Canada said an eastward low pressure system originating in Michigan was to blame. The rain is expected to continue Monday night and may not end until Thursday.
The forecast prompted a high-water safety bulletin from the Toronto and Region Conservation Authority. Significant rainfall will create swollen and fast-moving streams and rivers, the authority said.
People were urged to keep away from rivers, lakes and other bodies of water for the next couple of days.