(CNN) -- Hurricane Arthur is muscling up, gaining strength for its expected brush with the North Carolina coast Thursday night.
The storm, which developed into a hurricane early in the day, was expected to grow to Category 2 strength with winds of 105 mph before grazing the coast, then steadily weaken as it moves north, the National Hurricane Center said.
It's expected to bring storm surges of up to 5 feet, as well as large, damaging waves, high winds and dangerous rip currents that authorities warned could sweep even the strongest swimmers out to sea.
"This is no time to put your stupid hat on," North Carolina Gov. Pat McCrory told CNN's "New Day" on Thursday.
"Don't get brave just because you see some good waves out there," he said. "Stay out of the water ... and make sure we don't have to come rescue you and put our emergency workers in jeopardy."
Hurricane warnings and watches were up for most of the state's coastline. Parts of South Carolina and Virginia were under tropical storm warnings.
Authorities issued a mandatory evacuation order for Hatteras Island and a voluntary evacuation order for Ocracoke Island, both in North Carolina's Outer Banks.
"The focus right now is really getting people to evacuate," said Craig Fugate, director of the Federal Emergency Management Agency.
Track the storm
The storm interrupted some holiday plans, including a decision by the town of Surf City, North Carolina, to scrap its planned Thursday night Fourth of July show.
The city's website said the storm's fury is likely to be short-lived and encouraged visitors to keep their beach vacation plans: "Surf City is very much open for business."
But vacationers should not take the warm welcome as an all clear. To avoid tragedy, they should stay on land.
The storm is expected to spawn deadly rip currents: rapid flows of water from the shore back out to the ocean that can pull people to sea and exhaust even the strongest swimmers.
Tropical cyclones killed six people in 2009, the National Weather Service said. All drowned in large waves or rip currents.
Despite the warnings, a handful of families frolicked in the surf Thursday in Atlantic Beach, North Carolina.
Among them was Derek Cornwall's family, who arrived for vacation in the resort town late Wednesday night.
"We were banking on a couple of hours today before the storm moves in," he said.
His daughter, Hannah, was taking full advantage, playing in the waves despite being "a little nervous" about the storm.
"But I'm actually kind of excited because I've never been in a severe storm," she said. "It's kind of on my bucket list."
Robin Banning, her children and a friend planned to ride out the storm at a Walmart parking lot in Kill Devil HIlls, North Carolina. They had relocated there from an RV campsite closer to where the storm is expected to hit, but didn't want to go home to Virginia.
"I lived through Bertha," she said, referring to the 2008 hurricane. "This is good. It's just rain."
See Images as CNN crews cover Hurricane Arthur
Keeping the Boston Pops dry
Despite the risks farther south, the storm shouldn't force a total washout of East Coast Independence Day celebrations.
With rain forecast for parts of New England on Friday, the annual Fourth of July Boston Pops concert is being moved up a day to Thursday.
If it rains then, the fireworks part of the show can start, but the concert may have to go, event organizer Rich MacDonald told CNN affiliate WCVB. "It affects the instruments, and these instruments are valuable and old."
In the nation's capital, the weather looks cheerier for the holiday.
The slight chance of rain during the day Friday will vanish by night, leaving clear skies for the rockets' red glare of fireworks over the National Mall.