Periods of heavy rainfall, up to 50 mm in some areas, is expected for the region on Thursday.
Environment Canada has issued a rainfall warning for Chatham-Kent and Windsor-Essex.
The weather agency says most areas should see 20-30 mm of rain, while 40-50 mm is possible if heavy rain persists.
Officials say flooding is a possibility in low-lying areas and caution the public to steer clear of washouts near rivers and creeks.