A special weather statement has been issued for Windsor, Leamington and Essex County, along with Chatham-Kent and Rondeau Park.
Environment Canada says 15 to 25 millimeters of rain will fall between Saturday night into Sunday morning.
Gusty winds are also expected Sunday, with gusts up to 80 km/hour possible.
The forecast calls for rain beginning in the evening Saturday and taper off Sunday morning. There is also a thunderstorm risk over southwestern Ontario.
Pooling of water on streets with blocked storm drains and in low lying areas is possible.
