Former hurricane Hermine has regained strength as it moved slowly up the eastern side of the US.
Hermine has already caused two deaths, damaged properties and left hundreds of thousands without electricity from Florida to Virginia.
It spawned a tornado in North Carolina and closed beaches as far north as New York.
"This is not a beach weekend for anyone in the mid-Atlantic to the north-east," said Eric Blake, a hurricane specialist at the National Hurricane Centre in Miami.
Hermine rose up over the Gulf of Mexico and hit Florida on Friday as a Category 1 hurricane before weakening to a tropical storm across Georgia.
By 5am on Sunday, Hermine's top sustained winds remained at 65mph as it moved east-north-east at 12mph. The storm, expected to turn northwards later, was centred about 255 miles south-east of Ocean City, Maryland.
Forecasters expected Hermine to regain hurricane force on Sunday as it travels up the coast before weakening again to a tropical storm by Tuesday.
Governors all along the coast announced emergency preparations. Tropical storm warnings were in effect as far north as Connecticut.
And since sea levels have risen up to a foot due to global warming, the storm surges pushed by Hermine could be even more damaging, climate scientists said.
Michael Mann, at Pennsylvania State University, noted that this century's one-foot sea-level rise in New York City meant 25 more square miles flooded during Superstorm Sandy, causing billions more in damage.
"We are already experiencing more and more flooding due to climate change in every storm," said Michael Oppenheimer, a geosciences professor at Princeton University. "And it's only the beginning."
The winds and rain were so strong Saturday in North Carolina that all bridges to the Outer Banks were closed for several hours following a deadly accident.
Tyrrell County sheriff Darryl Liverman said that high winds tipped over an 18-wheeler, killing its driver and shutting down the US 64 bridge.
And on Hatteras Island in the Outer Banks, a small tornado spawned by Hermine knocked over two trailers and injured four people, authorities said.
Earlier in Florida, a homeless man died after being hit by a falling tree.
Hermine's timing could not be worse for coastal communities hoping for revenue from Labour Day events.
"This weekend would normally be a parking lot," said Jim Derrick. His family businesses include a mini golf course, sea shell store, indoor bounce house and ice cream shop in Rehoboth Beach, Delaware, where the beach was closed to foot traffic and swimming was prohibited on Saturday.
He called the weekend "definitely disappointing".
In Virginia Beach, the storm forced Bruce Springsteen to move a Saturday night concert to Monday.
Swimmers were ordered out of the surf in New York and New Jersey. And Amtrak cancelled or altered some service as the storm approached.