A Watershed Conditions Statement has been issued by the Essex Region Conservation Authority.
ERCA say rain gauges across the region recorded 10 millimetres on Monday night, saturating the ground and a system coming between Tuesday and Thursday could bring another 40-70mm which is 1.5 to 2.7-inches.
Heavier rain could fall during isolated thunderstorms, which could cause smaller watercourses to rise and spill their banks into adjacent low-lying areas.
A Watershed Conditions Statement will remain in effect until 5 p.m. Friday.
Environment Canada has also issued a Special Weather Statement warning of 50 mm of rain and potentially higher amounts in thunderstorms.