Storm Ernesto picked up strength as a hurricane on Monday as it headed further out in the Atlantic towards easternmost Canada.

But the storm is expected to stay offshore, causing powerful swells, dangerous surf and rip currents along the US east coast, the National Hurricane Centre said.

Ernesto’s maximum sustained winds increased on Monday to near 90 mph (150 kph), with higher gusts, the hurricane centre added.

It is expected to weaken and become a post-tropical storm by Tuesday.

The storm was centred about 320 miles (515 kilometres) southeast of Halifax, Nova Scotia, and was expected to pass near south-eastern Newfoundland late on Monday and early Tuesday, the centre said.

Some coastal flooding in Canada is possible.

The centre said people along the north-east coast should remain careful.

“We would certainly encourage anyone going to beaches, really, anywhere along the US east coast to just pay attention to whatever flags are up, whatever lifeguards are saying, and stay out of the water if it’s not safe,” David Zelinksy, lead meteorologist with the hurricane centre.

Swells generated by Ernesto were affecting portions of the Bahamas, Bermuda and the US east coast, as well as the Canadian Atlantic coast.

Life-threatening surf and rip current conditions are likely in these areas during the next couple of days.

The weather service posted a coastal flood advisory and warned of a high risk for rip currents along the Atlantic coast throughout Monday evening, saying they “can sweep even the best swimmers away from shore into deeper water”.

A warning extended from Florida to the Boston area and portions of Maine.

Forecasters, citing local emergency management, said a 41-year-old man drowned on Saturday in a rip current at Surf City, North Carolina.

And two men drowned off South Carolina’s Hilton Head Island on Friday where rip current warnings were posted.

They were identified as Ralph Jamieson, 66, of South Euclid, Ohio, and Leonard Schenz, 73, of Loveland, Ohio.

It could be weeks before autopsy results can determine whether the deaths were related to Ernesto, Beaufort county coroner David Ott said.

Over the weekend, Ernesto initially had weakened to a tropical storm late on Saturday after bringing heavy rain and strong winds to Bermuda, but no injuries were reported, Bermuda security minister Michael Weeks said on Sunday afternoon.

Ernesto previously battered the north-eastern Caribbean, leaving tens of thousands of people without water in Puerto Rico.

After cleaning up and removing debris, the Virgin Islands Department of Education said all public schools would resume operations on Monday.

Public school classes also were slated to start on Monday in Puerto Rico, nearly a week after the original opening date.

Flooding in Connecticut from a storm that dropped as much as 10 inches (25.4 centimetres) of rain Sunday was unrelated to Ernesto, weather officials said.

The rain washed away roads, flooded basements, and led to rescues and at least one death.

In the eastern Pacific Ocean, Tropical Storm Gilma strengthened but was forecast to remain away from land this week.