09/04/2012 08:07 EDT | Updated 11/04/2012 05:12 EST

Remains Of Isaac Drench Ontario

The remains of Hurricane Isaac held out longer than expected and delivered an unexpected punch to southeastern Ontario on Tuesday, dumping as much as 70 millimetres on cities including London, Toronto and Peterborough.

The storm that last week menaced New Orleans and the U.S. Gulf states was originally expected to fizzle out into isolated showers and cloud cover by the time it reached Canada, according to CBC meteorologist Giselle Dookhie.

Instead, the storm formerly known as Isaac let loose with heavy rain and thunder.

"What happened is the remnants of Isaac were held back by high pressure over much of Ontario and eastern United States," said Dookhie.

High pressure systems usually weaken such storms but this one managed to stay intact while moving north, dumping moisture collected over the Gulf of Mexico on Ontario and parts of the U.S. northeast.

Environment Canada rainfall warnings remain in effect for Toronto and Peterborough, with another 20-30 millimetres of rainfall predicted for overnight. The rain is headed for the Ottawa area.

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