Meanwhile, in the Pacific, Hurricane Olivia, forecast to weaken to a tropical storm, may hit Hawaii as soon as Tuesday.
Tropical Storm Isaac is also strengthening over the eastern tropical Atlantic and is expected to become a hurricane by late Sunday.
The station, the largest naval complex in the world, said in a Facebook post that much of the base is prone to heavy flooding, especially the parking lots adjacent to the waterfront.
Speaking to reporters on Sunday, South Carolina Gov. Henry McMaster said Florence could grow into a powerful Category 4 storm by Thursday, striking with winds ranging from 130 to 150 miles per hour. The National Hurricane Center says it's still too early to predict the storm's exact path.
McMaster, predicting a "likely strong hit on SC", stressed that residents should begin planning now to evacuate if necessary.
The governors of North and SC and Virginia declared states of emergency to give them time to prepare, and the Navy said ships in Virginia's Hampton Roads area would leave port for their own safety.
No impacts are expected in Northwest Florida yet, but locals and visitors should remain vigilant as we enter the most active part of hurricane season.
In Charleston, South Carolina, along the coast, city officials offered sandbags to residents. "With Florence quickly approaching, I'm urging all Georgia residents to take action to protect themselves, their homes and their businesses".
Carnival Cruise Line said Sunday that it had changed the schedule of its cruise ships to accommodate tropical weather threats. Instead the ship will now head to The Bahamas. It is expected to arrive in NY on September 13.
A tropical storm warning and hurricane watch are in effect for the Cabo Verde islands of Santiago, Fogo, and Brava.
Florence regained Hurricane strength this morning, and is considered a potential threat as it is expected to pass within 460 miles of the island in the next 72 hours.
The South Carolina Emergency Management Division, on the other hand, took to Twitter to announce that officials are "preparing for the possibility of a large-scale disaster".
All three governors urged residents to assemble emergency kits including food, water, medications, pet supplies and important documents that might be needed if evacuations are necessary.
Forecasters predicted it would become a risky Category 4 storm before a possible landfall Friday.
"What that means for us is whatever happens, we're going to have a lot of rain and a lot of wind", he said, adding, "Presume that a major hurricane is going to hit right smack dab in the middle of SC".
Storm-force winds could begin buffeting the Carolina coast by Wednesday night, the NHC said.
Hurricane Olivia, according to the Central Pacific Hurricane Center's advisory issued at 11 a.m. ET Sunday, is approaching Hawaii with maximum sustained winds near 80 miles per hour and is expected to remain at hurricane strength through Monday evening.