Environment Canada says a developing fall storm will bring rain and strong winds to southern Ontario at mid-week.
Sarnia-Lambton is included in a special weather statement issued late Monday afternoon.
The national weather agency says a disturbance over the American Midwest will merge with moisture from the remnants of Hurricane Patricia and track over the Great Lakes.
Rain, heavy at times, is forecast to spread into southwestern Ontario late Tuesday night and reach the Golden Horseshoe area by Wednesday morning.
Between 25 mm and 40 mm of rain (1 to 1.5 in) is likely for most areas.
Strong southwesterly winds with gusts to 70 km/h are expected to develop over southwestern Ontario Wednesday.
Wind gusts could approach the warning criterion of 90 km/h near the eastern ends of Lake Erie and Lake Ontario.
