The Canadian Hurricane Centre in Halifax said the Category 1 hurricane was centred off North Carolina early Saturday and was expected to move up the eastern seaboard of the United States and through Long Island and into Maine late Sunday, before entering eastern Canada as a tropical storm.
"When it gets to us those weather elements (wind and rain) tend to separate and so the heaviest rains shift to the left of the track and the heaviest winds shift to the right of the track," said centre forecaster Peter Bowyer.
Bowyer said as a result the heaviest rains were expected in northwestern New Brunswick and in the eastern townships of Quebec into early Monday, while areas to the east of the storm's centre would see the heaviest winds.
"We're looking for the winds to be probably below hurricane strength when they arrive in Canada. It's more a swath of wind and a swath of rain that's coming with this," said Bowyer.
Nonetheless, he said the storm could pack a significant punch.
He said coastal areas of the Maritimes including Nova Scotia and New Brunswick could see heavy bands of rain begin on Sunday and then experience sustained winds of 90 kilometres an hour on Monday with hurricane force gusts of up to 120 kilometres an hour. There was also a significant threat of storm surge along the Bay of Fundy coast because of the potential for unusually high tide levels.
Bowyer said the potential also remained for up to 100 millimetres of rain to fall in parts of northwestern New Brunswick and into the Gaspe Peninsula. He said a heavy rainfall warning had also been issued for Quebec's eastern townships.
The heaviest part of the downpour could fall within a two to four hour period.
"Which then of course is a huge problem for potential flash flooding or hydroplaning if you are out there driving," Bowyer said.
Much of P.E.I. and parts of eastern Labrador were also expected to be hit with significant winds and rain on Monday.
Meanwhile, dozens of flights were cancelled to the northeastern United States on Saturday by airports in Toronto, Ottawa, Montreal and Halifax.
More than 80 flights at Toronto's Pearson International Airport involving eastern U.S. cities including Washington, Philadelphia, New York, Boston and Raleigh, N.C., were called off.
Air Canada said flights involving airports in Atlantic Canada might also be affected by the storm and travellers were encouraged to check the status of their flight online before heading to the airport.
And the federal government also urged Canadians residing or travelling on the U.S. east coast to follow local advice on hurricane Irene.
The minister of state for foreign affairs, Diane Ablonczy, said Canadians in the affected areas should exercise caution, monitor local news and weather reports and follow the advice of local authorities.
By mid-afternoon Saturday the U.S. National Hurricane Centre said Irene was maintaining its strength as it moved across North Carolina toward southeastern Virginia with sustained winds of about 137 kilometres an hour.