By Rich McKay and Letitia Stein

(Reuters) – North Carolina officials on Monday ordered residents to evacuate the state’s Outer Banks barrier islands beginning on Monday ahead of Hurricane Florence, the first major hurricane to threaten the eastern United States this year.

With winds of 115 miles per hour (185 kph), the storm had reached Category 3 strength on the five-step Saffir-Simpson scale by 11 a.m. on (1500 GMT) on Monday, according to the National Weather Service.

It warned the storm would be “an extremely dangerous major hurricane” by the time it made landfall, forecast in the Carolinas on Thursday.

The hurricane was gaining strength as it traveled over warm Atlantic waters, about 1,240 miles (2,000 km) east-southwest of Cape Fear, North Carolina, the National Hurricane Center said in an advisory.

All of Hatteras Island was under mandatory evacuation order and other parts of the Outer Banks will have to evacuate by 7 a.m. EDT (1100 GMT) on Tuesday, Dare County Emergency Management said in a statement.

Hurricane-force winds could buffet the Carolinas by Wednesday night with landfall likely in South Carolina and North Carolina on Thursday, followed by heavy rains that could cause flooding in much of the U.S. Southeast, the NHC said.

The governors of Virginia, North Carolina, and South Carolina all declared states of emergency.

Residents as far north as Virginia were warned that Florence could bring a life-threatening coastal storm surge, as well as inland flooding from “prolonged and exceptionally heavy rainfall,” the NHC said.

North Carolina Governor Roy Cooper urged his state’s residents to get ready, noting the storm was generating swelling waves and dangerous currents.

NHC spokesman Dennis Feltgen said historically, 90 percent of fatalities from hurricanes, tropical storms, and tropical depressions have been caused by water. Some 27 percent of the deaths have come from rain-driven flooding, sometimes hundreds of miles inland.

The NHC also was tracking two other hurricanes farther out in the Atlantic.

Isaac strengthened into the fifth hurricane of the 2018 Atlantic season on Sunday, the NHC said, and as of early Monday, it was about 1,230 miles east 1,305 miles (1,985 km) east of the Windward Islands with maximum sustained winds of 75 mph (120 kph).

Hurricane Helene was spinning in the Atlantic off West Africa’s Cape Verde islands with 85-mph (140-kph) winds on Monday but did not appear to pose an immediate threat to land.

As Florence gathered strength far out in the Atlantic, Wall Street was trying to pick winners and losers from any havoc it might cause.

Generac Holdings Inc, building materials maker Owens Corning and roofing supplier Beacon Roofing Supply Inc, which were up between 4 percent and 8 percent. Retailers Lowe’s Companies Inc and Home Depot Inc gained more than 2 percent.

On the downside, several insurers that are seen vulnerable to potential claims losses slipped, led by a 1.8 percent drop in Allstate Corp and a 1.7 percent decline in Travelers Companies Inc.

(Reporting by Rich McKay in Atlanta, Letitia Stein in Tampa, Florida, and Bernie Woodall in Fort Lauderdale, Florida; Editing by Alison Williams and Bill Trott)