A special weather statement was posted for Sarnia-Lambton Friday afternoon, advising of heavy rainfall throughout the weekend.
Environment Canada said rainfall rates of up to 40 millimetres per hour are possible through Sunday.
"The heaviest rainfall is expected on Saturday. Locally higher amounts are possible Saturday afternoon and evening," the agency said.
Heavy downpours can cause flash floods and water pooling on roads.
Localized flooding is also possible in low-lying areas.