Hurricane Lee is heading north up the Atlantic and is expected to make landfall around Maine and Nova Scotia by this weekend.
A category one storm as of Friday evening, Lee is expected to bring “hurricane conditions” to Canada’s Atlantic provinces.
Millions in coastal New England and parts of Canada are under storm warnings.
US authorities said it will be “large and dangerous”.
The storm has sustained wind speeds of 80mph (128km/h) and is currently 290 miles south of Nantucket, Massachusetts, the National Hurricane Center (NHC) said.
Lee, which is a couple of hundred miles north of Bermuda, has already whipped up strong winds and caused power outages throughout those islands.
The NHC said Lee will still be “a large and dangerous cyclone” that will bring strong winds, heavy rain and coastal flooding.
Because of the storm’s widening size, people will feel its impacts well beyond where the centre makes landfall.
“These conditions are likely to lead to downed trees and potential power outages,” the NHC said.
The centre said swells generated by Lee could produce “localised urban and small stream flooding”, especially in portions of eastern Maine, New Brunswick and western Nova Scotia into Saturday.
Maine Governor Janet Mills declared a state of emergency and US President Joe Biden ordered resources from the Federal Emergency Management Agency to be deployed, in anticipation of the storm.
The state is expecting 20ft (6m) waves and wind gusts up to 70mph.
Lee is expected to dump its heaviest rain over Maine. Parts of New Hampshire, Massachusetts and Rhode Island will also have intense rainfall.
The last hurricane to hit Maine was Hurricane Gerda in 1969. In 1991, Hurricane Bob was downgraded to a tropical storm just before making landfall.
The Canadian Hurricane Centre has also issued hurricane and tropical storm watches for parts of Nova Scotia, New Brunswick and Prince Edward Island.
Wildlife parks in Nova Scotia will be closed on Friday as Lee creeps towards the region.
“We are closing our parks for the storm and will reopen when it is safe,” said Tory Rushton, provincial minister of natural resources and renewables.
Nova Scotia Power said it has been preparing for potential power cuts because of the storm.
“Any kinds of preparations should be completed by late this afternoon, early evening at the latest because we are going to see some of that rain and winds are gradually going to start to pick up,” forecaster Bob Robichaud said.
In Halifax, shelters have been set up for unhoused people so they can stay safe during the storm.
How much damage the storm will cause depends on its trajectory and any directional shifts before landfall. It is currently moving northward at a speed of 18mph.
