Florence may gain hurricane intensity through week

BOSTON — A strengthening Tropical Storm Florence is casting a hurricane-size shadow across the U.S. East Coast, where there is a risk it will strike late this week.

The chances of Florence hitting the U.S. have increased as the storm drifted west across the central Atlantic Ocean. Florence was about 790 miles southeast of Bermuda, with tropical-storm strength winds of 70 mph, the National Hurricane Center said in a 10 p.m. advisory. It was moving west at 6 mph.

Florence is expected to become a major hurricane by Monday, the center said, adding that “a rapid intensification” is forecast to begin today.

The storm is forecast to travel between Bermuda and the Bahamas on Tuesday and Wednesday before approaching the southeastern U.S. coast on Thursday, the weather center in Miami said.

“Florence is forecast to be a dangerous major hurricane near the southeast U.S. coast by late next week, and the risk of direct impacts continues to increase,” the hurricane center said. People should have a personal hurricane plan, it said.

“We are in a serious situation, we have major hurricane potentially making landfall on the East Coast next week,” Jeff Masters, co-founder of Weather Underground in Ann Arbor, Mich., said by telephone. “I would say it has about a 70 percent chance to hit the U.S. East Coast and a 30 percent chance it recurves.”

Governors in both South Carolina and Virginia declared states of emergency Saturday to give their states time to prepare for the possible arrival of the storm. South Carolina Gov. Henry McMaster emphasized that there’s no way to know yet when and where the storm will hit land, or when evacuations might be called.

On Friday, North Carolina Gov. Roy Cooper declared a state of emergency and urged residents to use the weekend to prepare for the possibility of a natural disaster.

“We are entering the peak of hurricane season and we know well the unpredictability and power of these storms,” Cooper said.

The Navy is making preparations this weekend for its ships in the Hampton Roads, Va., area to leave port. The U.S. Fleet Forces Command said in a news release Saturday that the ships will get ready in anticipation of getting underway Monday to avoid storm damage.

Adm. Christopher Grady said in a statement that the decision was based on Florence’s current track, which indicates the area could see strong sustained winds and storm surges.

The news release notes that plans could change if forecasts indicate a decrease in the strength or change in the track of the storm.

Hurricane track and intensity forecasts often have wide margins of error beyond five days. The earliest Florence may approach the U.S. coastline would be Thursday or Friday, but meteorologists are warning everyone from Florida to Massachusetts to pay close attention.

“People don’t need to go out and start boarding up windows and stocking up on supplies just yet,” said Mike Doll, a meteorologist at AccuWeather Inc. in State College, Pa. “By the time we get to Thursday, the expectation is it will be off the southeast coast of the U.S.”

The East Coast’s fate from the current storm will be decided by a weather pattern called the Bermuda High. A semipermanent feature in the Atlantic, the high rotates in a clockwise manner and will steer Florence through the ocean.

“Florence is tracing out a clockwise path around the high,” Masters said. “When it reaches the edge of the high, it will start to turn north.”

If the high’s edge is offshore, then Florence could miss the East Coast entirely. But if it’s overland or close to the seaboard, then the storm will strike land, he said. The forecast picture will become clearer through the weekend.

“By the time we get to early Monday we’re going to have a better idea of what portions of the East Coast will be directly impacted,” Doll said.

Nine storms have emerged across the Atlantic so far this year. To the east of Florence, forecasters also are watching tropical storms Helene and Isaac. Helene is forecast to brush the Cabo Verde Islands off Africa before drifting into the central Atlantic, while Isaac could grow to a hurricane and threaten the small islands in the Caribbean Sea by Thursday.

Meanwhile, in the Pacific, Hurricane Olivia, forecast to weaken to a tropical storm, may hit Hawaii as soon as Tuesday.