Chris Fogarty, manager of the centre in Halifax, said it's difficult to predict where in Newfoundland the storm will land because its circulation is about 800 kilometres in diameter.
"The centre of the storm is not the area of most concern," said Fogarty in an interview. "It would actually be well outside that area because the storm is likely to be so large that the impact zone will be quite extensive."
Fogarty said winds could gust up to 100 km/h in Newfoundland and Cape Breton when it hits on Tuesday.
He said a front that was stalled over New Brunswick and western Nova Scotia on Sunday will stream moisture northward and will merge with some of Leslie's moisture and clouds when it arrives, significantly increasing the threat of heavy rainfall.
Newfoundland, Nova Scotia and P.E.I. could see 100 to 150 millimetres of rain over about 36 hours, Fogarty said.
He said Leslie was expected to reach hurricane status sometime Sunday or Monday, but he could not say if it will maintain that status for its arrival in Atlantic Canada.
"It will possess high winds for sure, whether it will be at hurricane strength or not, that still remains to be seen," said Fogarty. "We basically want to brace Newfoundland for the potential for hurricane force winds."
Forecasters said the small Category 2 hurricane Michael will likely be pushed northward out of the area by Leslie.
But the hurricane centre is still monitoring the interaction between the two storms, Fogarty said.
"We'll keep an eye on it because we don't... have experience with those types of systems," he said. "You don't usually have them that close, and they're going to get closer.
"But I don't think they'll get close enough that they become intertwined."
Leslie was about 230 kilometres southeast of Bermuda on Sunday.
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