A tornado watch is in effect for Windsor-Essex and Chatham-Kent.
Environment Canada says conditions are favourable for the development of severe thunderstorms that may produce tornadoes.
The weather agency says strong winds, large hail and heavy rain are also possible.
Thunderstorms are developing over Michigan and are expected to track eastward into Ontario.
Environment Canada Warning Preparedness Meteorologist Geoff Coulson says there are very intense thunderstorms already occurring in southwestern, lower Michigan.
"This is the type of day to keep a close eye on the latest statements from Environment Canada as we track these storms and also to keep a close eye on the sky especially to the southwest which is where these storms are developing, generally moving from southwest to northeast," says Coulson.
He says lots of rain, large hail and damaging winds are also possible.
"There is a risk of strong thunderstorms and the possibility of tornado from late this morning through late this afternoon in the Windsor and Essex County area," he says. "Definitely a day to stay on top of the latest statements from Environment Canada and keep a close eye on the sky."
Coulson says residents should be prepared for severe weather and take cover immediately if threatening weather approaches.
Forecasters say the timing of the storms is late this morning into this afternoon.
Tornadoes are possible when a tornado watch is issued. When a tornado warning is issued, a tornado is imminent.
— with files from AM800's Paul McDonald & Rob Hindi