Hurricane Erin weakens to post-tropical cyclone

Strong winds and waves have combined with dangerous rip currents as Hurricane Erin made its way farther out to sea off the United States' east coast.

The storm was forecast to cause possible coastal flooding into the weekend but was also expected to gradually lose strength.

The US National Hurricane Center in Miami reported on Friday evening that Erin had weakened into a post-tropical cyclone, with maximum sustained winds of 150km/h, and was located about 600km south-southeast of Halifax, Nova Scotia.

Despite being twice the size of an average hurricane, Erin so far has managed to thread the needle through the Atlantic between the East Coast and several island nations, limiting its destructiveness.

Massachusetts-based meteorologist Caitlyn Mench on Friday said Erin's high wind field caused it to be felt widely along the east coast: "On a positive note, it passed all offshore," she said of the New England area, which experienced some minor coastal flooding due to the storm.

Although damage assessments were still under way, the low-lying islands appeared to have dodged widespread trouble.

A tropical storm warning was lifted for Bermuda, where residents and tourists had been told to stay out of the water through Friday. Warnings along the coasts of North Carolina and Virginia were also discontinued.

The National Weather Service issued coastal flood warnings for places as far north as the Mid-Atlantic and New England coasts, saying that some roads could be made impassable.

Erin has fluctuated in intensity since forming nearly a week ago but has remained unusually large, stretching across more than 960km.

So-called Cape Verde hurricanes like Erin, which originate near those islands off the west coast of Africa, cross thousands of kilometres of warm ocean and are some of the most dangerous to North America.