As Hurricane Lee moved north through the Atlantic early Friday, tropical storm warnings were in effect for parts of Canada and a wide stretch of coastal New England that included about seven million people in Maine, Massachusetts and New Hampshire.

Lee has been spinning across the Atlantic for more than a week and was still hundreds of miles away from New England early Friday as it produced tropical storm conditions in Bermuda. But conditions were forecast to deteriorate in the northeastern United States and Canada later in the day.

Government leaders across New England and Canada have issued alerts and warnings anticipating the arrival of a powerful hurricane this weekend, though a small shift east or west will could make a significant difference in how damaging the storm will ultimately be, and where.

The ultimate outcome for locations in New England will depend on how a few different conditions play out over the next two days. The amount of rainfall will vary significantly depending on precisely where the storm comes ashore, and the forecast rainfall amounts are likely to shift until the very last minute.

As of 5 a.m. on Friday, Lee was about 215 miles west-northwest of Bermuda and about 490 miles south-southeast of Nantucket in Massachusetts. It had maximum sustained winds of 85 m.p.h., making it a Category 1 storm, and was moving north at 16 m.p.h. Though the storm is expected to weaken, the Hurricane Center said it would remain “a large and dangerous cyclone” as it approaches New England and Atlantic Canada.

A hurricane watch, meaning hurricane conditions are possible within the area, stretched through down-east Maine from Stonington to the U.S.-Canada border. Gov. Janet T. Mills of Maine declared a state of emergency on Thursday, and the White House ordered federal assistance to the state.

The Canadian Hurricane Center also issued a hurricane watch on Wednesday for part of the provinces of New Brunswick and Nova Scotia. The center said that its hurricane and tropical storm watches referred to conditions expected on Saturday.

A tropical storm warning, meaning winds of 39 miles per hour or higher are expected within about 36 hours or less, was in place from Westport, on the South Shore of Massachusetts, and the islands of Nantucket and Martha’s Vineyard through parts of New Brunswick and Nova Scotia in Canada. Forecasters warned that the growing size of the storm means hazards will extend well away from the center.

The storm was moving north after passing Bermuda on Thursday. By Friday night and into Saturday, Lee was expected to turn slightly left, bringing the large hurricane close to southeastern New England.

Bob Robichaud, a warning preparedness meteorologist with the Environment and Climate Change Canada, said at a news conference on Thursday that Lee’s anticipated turn northward would bring Lee “into our response zone on Friday, again, most likely as a hurricane.”

Officials in Boston were hopeful after Lee turned “slightly east” on Thursday morning.

“At this time, we are expecting the worst of it to miss Boston, which is good news,” said Mayor Michelle Wu of Boston at a news conference on Thursday. “Fingers crossed that will remain the projection.”

But she said conditions were expected to be similar to that of a nor’easter because the wind and the rain will extend far beyond the center over the coast.

The city expects to receive four inches of rain with wind speeds up to 30 miles per hour as the storm arrives late on Friday evening and lasts through Saturday evening, Mayor Wu said.

The city of Quincy, Mass., just south of Boston, said it was installing floodgates on Thursday to close gaps in its sea wall.

Southampton, a town on the eastern tip of Long Island in New York that is threatened by high tides and coastal flooding, declared a state of emergency, beginning on Thursday and stretching through the weekend.

Anne Strauser, a meteorologist with the National Weather Service, said that the worst-case scenario for Maine would be if the storm shifts farther west and creates more onshore flow, which could make coastal flooding worse. She said that any storm surge that occurred there would vary depending on the tide cycle. Unlike when a hurricane makes landfall in the southern United States, and the tides vary by a few feet, the tide swings in Maine can be from eight to 18 feet. So a storm surge at low tide might not have much of an effect.

As the storm heads north, it will weaken as it moves over cooler water. And as it approaches land, it’s likely to transition from a tropical system — one that gets its energy from the ocean — into one similar to Hurricane Sandy’s, which drew energy from competing cold and warm air masses.

While weakening is good, it will not diminish the potential impact of wind, rain and coastal flooding. This storm is already on the larger side for a hurricane in terms of how wide it is,” Ms. Strauser said. “And it’s just going to get wider as it moves north.”

In Canada, officials are concerned that because of Lee’s broadness, it is likely to affect most of the Maritime Provinces and parts of eastern Quebec.

Hurricane-force winds extended up to 105 miles from the center of the storm on Friday morning, and tropical-storm-force winds extended to more than triple that distance.

Western Nova Scotia faces some of the highest possible impacts from Lee, Environment Canada said.

Johnny Diaz, Melina Delkic, Mike Ives, Orlando Mayorquin, Anastasia Marks, Eduardo Medina, Chris Stanford, John Yoon and Derrick Bryson Taylor contributed reporting.