A special weather statement is in effect for Windsor-Essex and Chatham-Kent.
The statement has since been rescinded for Sarnia-Lambton.
Environment Canada said heavy rain is possible Tuesday night.
Showers and thunderstorms have developed in Michigan and will slowly move across the area, possibly dropping 20-40 millimetres of rain.
The National Weather Service in Detroit/Pontiac has also issued a Flash Flood Warning for the area, including Detroit until 10:45 p.m.