The agency's forecast calls for the stormy weather to arrive in the city, as well as much of the GTA, this afternoon, bringing with it wind and rain.
"Conditions are favourable for the development of dangerous thunderstorms that may be capable of producing damaging wind gusts, large hail and heavy rain," Environment Canada said on its website.
Anyone outside should brace for winds gusting up to 50 km/h.
Wednesday's high is expected to reach 26 C.
Temperatures are expected to remain hot until Sunday.