Browning's choice to stay in the hurricane warning zone wasn't easy, she said, but she "could not find anywhere to go".
But the storm still carried "very risky winds", the Center added. It is now at Category 1.
Florence is expected to go move slowly as it approaches North and SC, whipping hurricane-force winds and dumping relentless rain at least through Saturday.
"Just because the wind speeds came down and the intensity of this storm came down to a Category 2, please do not let your guard down", Brock Long, the Federal Emergency Management Agency administrator, told reporters Thursday in Washington.
Hurricane Florence brought a storm surge of some 3 meters (10 feet) as it began battering the USA east coast early on Friday. From a large gray conference room in the center, they have monitored the path of the storm, coordinated with local partners to open shelters and evacuate residents, mobilized first responders, hoped for the best and prepared for the worst.
"Catastrophic effects will be felt outside the center of the storm due to storm surge", North Carolina Gov. Roy Cooper said Thursday morning.
Images captured by Associated Press journalists show last-minute preparations to secure homes and businesses and families settling into storm shelters as rain and storm surge began to soak the Carolinas.
Atlantic Beach on North Carolina's Outer Banks islands had already received 30 inches (72 cm) of rain, the U.S. Geological Survey said, while more than 25 inches (63 cm) have fallen in the Newport, Morehead City area since Thursday.
Myrtle Beach, a SC beach resort, was virtually deserted with empty streets, boarded up storefronts and very little traffic.
"We live in a mobile home so we were just like 'No way, '" she said. "I've got four cats inside the house". "But we can't replace us so we made a decision to come here".More news: The truth about Serena Williams' US Open drama
More news: Apple 2018 Event Recap: iPhone Xs, Xs Max, Xr, Apple Watch
More news: Trump’s Hurricane Maria Tweets Get Rare Republican Pushback In Florida
By mid-afternoon the winds had dropped to 75 miles per hour (120 kph) and the centre was moving west at 6 miles per hour (10 kph), the NHC said, and parts of North and SC would get as much as 40 inches of rain (1 metre).
By Friday evening, Florence was downgraded to a tropical storm, its winds weakening to 70 miles per hour as it pushed inland.
He said hurricane-force winds extend outward 80 miles from the center of the storm and tropical storm-force winds extend almost 200 miles out.
Hurricane Florence is on a path of destruction that will put millions of people at risk and threaten billions of dollars in property damage, centered on the Carolinas.
The NHC warned that storm surge could still reach up to three metres high between North Carolina's Cape Fear and Cape Lookout, though it could be higher in the Bay, Neuse, Pamlico and Pungo Rivers, it said.
A state of emergency has been declared in five coastal states - North Carolina, South Carolina, Georgia, Maryland and Virginia.
Duke Energy, the major power supplier for North and SC, told the New York Times on Wednesday that the storm could knock out power for up to 3 million customers across the two states.
The page says service animals aren't barred from evacuation shelters, beaches shouldn't be used for sand bags, and evacuation orders aren't enforced by FEMA.
"We're a little anxious about the storm surge so we came down to see what the river is doing now", said Linda Smith, 67, a retired nonprofit director.
"Either no (hotel) rooms are available, or we are denied because the breed or size of dogs", she said.