Environment Canada said conditions were favourable for the development of severe thunderstorms on Wednesday.
A severe thunderstorm watch was posted for Sarnia-Lambton just before 1:30 p.m.
Forecasters said isolated thunderstorms were expected to develop in the afternoon and track over the area.
These thunderstorms were expected to move east of the area later in the evening.
Strong wind gusts of 90 kilometres per hour, and large hail up to three centimetres was possible.
Emergency Management Ontario recommends that you take cover immediately if threatening weather approaches.
Strong wind gusts can damage trees, buildings and overturn vehicles.
Severe thunderstorm watches are issued when conditions are favourable for the development of thunderstorms capable of producing damaging hail, wind or rain.