Environment Canada is tracking an area of severe thunderstorms capable of producing strong wind gusts, up to nickel size hail and heavy rain.
The weather office upgrading the severe thunderstorm watch to a warning.
Thunderstorms from Sarnia to Woodstock will continue over the next few hours and are moving southeastward to Hamilton and Niagara.
Heavy rain with near 50 millimetres in an hour and wind gusts to 90 kilometres per hour are the main threats.
Total rainfall amounts in excess of 50 millimetres are possible this morning in localized areas.