Environment Canada issued a special weather statement for the London and Middlesex area with significant rainfall expected later Tuesday.
The special weather statement is in effect for London, Strathroy, Parkhill, Komoka, and eastern and western Middlesex County.
The national weather agency said between 20 to 30 millimetres are expected to fall as a low-pressure system moves into the southwest region.
The rainfall is expected to taper off into Tuesday evening.
Locally, higher rainfall amounts of 30 to 40 mm are possible in areas that receive heavy downpours during a thunderstorm, Environment Canada said.
Heavy downpours can cause water pooling on roads.
Motorists are advised to allow extra time to reach their destination.