Environment Canada has not only confirmed a tornado touched down in southwestern Ontario on Thursday, it says the twister was the strongest in years.

The Ontario Provincial Police had given the initial report of a weak tornado between Tillsonburg and Delhi, moving towards Simcoe.

Environment Canada said its initial investigation gave the tornado a ranking of F2, with wind speeds of between 181 and 252 kilometres per hour. The Fujitsu scale goes from F1 to F5, the strongest.

This is the third tornado to form in Ontario so far in 2009, and the strongest in almost three years.

No injuries were reported, but one house lost a roof, and a barn suffered some damage.

Toronto suffered a drenching, and there were reports of some hail in the city and the GTA associated with the storm activity. Temporary local flooding also occurred due to the intense rainfall.

The Toronto Police Service warned people to adjust their driving to the weather conditions.

Firefighters in Thornhill had to respond to a home where lightning caused a small fire in the attic.

Near the Toronto Island airport, a boat capsized. The Toronto police marine unit successfully rescued five people. A salvage operation will be carried out on Friday to right the partially-submerged 40-foot vessel.

As of 8 p.m., Environment Canada had lifted most of the weather warnings it had in place. London and Elgin County remain under a thunderstorm watch, as do Hamilton and the Niagara peninsula.

There are no warnings for Thursday night for Toronto or the surrounding GTA.

CTV weather anchor Tom Brown said we've had three days of hot, humid air. And when you get a cold front rolling through as Ontario did on Thursday, you get the conditions for thunderstorms and possibly tornadoes.

Toronto and Hamilton may get some showers yet Thursday night from the northwest, with the possibility of hail, heavy rain and wind gusts.

However, he was predicting about two to five millimetres of rain would fall.

With files from The Canadian Press