Florence Gains Strength As A Category 4 Hurricane, Aiming At U.S. East Coast

Enlarge this image toggle caption National Hurricane Center National Hurricane Center

Updated at 5 a.m. ET on Tuesday

Hurricane Florence is growing in size and strength as it barrels toward the Southeastern U.S. for an expected landfall in the Carolinas later this week as an "extremely dangerous hurricane," according to the National Hurricane Center.

A hurricane watch has been issued for the U.S. east coast from Edisto Beach, South Carolina to North Carolina-Virginia border, including the Pamlico and Albemarle sounds., with storm surge watches encompassing the same area.

Enlarge this image toggle caption National Hurricane Center National Hurricane Center

Swells generated by the hurricane are already affecting portions of the East Coast and Bermuda. The center said the powerful waves are likely to cause life-threatening surf and rip current conditions. Additionally, Florence, about 1,000 miles southeast of Cape Fear, N.C., is predicted to bring "life-threatening impacts" to North Carolina and neighboring states late this week.

Mandatory evacuation orders have been issued by the governors of North and South Carolina and Virginia for coastal areas.

The storm quickly strengthened on Monday and by midday was reclassified as a Category 4 hurricane, reaching that status a day earlier than experts had predicted. The hurricane center cited data from a NOAA Hurricane Hunter aircraft that showed Florence was rapidly intensifying, with maximum sustained winds near 140 mph.

In an earlier update, officials said Florence's winds could reach 150 mph over the next 36 hours. The storm is already 500 miles wide — meaning a large area will be at risk when it nears land. The NHC says hurricane-force winds can be expected 40 miles from the center of Florence, while tropical-storm force winds extend out 150 miles.

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The hurricane's impacts could range from a strong storm surge to flooding from torrential rainfall and hurricane-force winds. Forecasters warn that the predicted track is likely to change — but for now, it shows the strong hurricane bearing down on the North Carolina coast, with a potential landfall north of Wilmington.

Once it makes landfall, Florence is predicted to stall and remain over North Carolina for at least 24 hours — increasing the threat of dangerous flooding, NHC Director Ken Graham said on Monday. Even in areas far from the coast, he added, parts of North Carolina and Virginia could see rain totals of 10-15 inches over the next seven days.

As of 5 a.m. ET Tuesday, Florence was moving at 15 mph, some 500 miles south-southeast of Bermuda, the hurricane center said.

As it nears the U.S. Atlantic shore, Florence will also benefit from "very warm" sea surface temperatures of up to 85 degrees, the hurricane center said.

As meteorologist Stu Ostro of The Weather Channel reports via Twitter, since 1851, only four Category 4 hurricanes have made landfall north of Florida on the East Coast. The northernmost landfall was made by Hazel, a devastating and deadly storm that struck close to the South Carolina/North Carolina border in October 1954.

Forecasters say Florence will pass between Bermuda and the Bahamas on Tuesday and Wednesday and start its approach to the U.S. on Thursday morning. Tropical-storm-force winds are expected to start to reach the coast of the Carolinas on Thursday, the National Hurricane Center said.

As the danger became clear over the weekend, the governors of North Carolina, South Carolina and Virginia all declared states of emergency. They urged residents to fortify homes and gather supplies.

The U.S. Navy is also taking precautions, with the U.S. Fleet Forces Command ordering nearly 30 ships in the Hampton Roads area of the Virginia coast to head out to sea to avoid the storm. Vessels that can't leave port will prepare by a variety of means, from adding mooring and storm lines to dropping anchor and disconnecting shore power cables.

Florence is currently projecting hurricane-force winds (74 mph and higher) up to 30 miles from its center. Forecasters say that because of the size the storm is expected to attain, it will wreak havoc regardless of how strong its winds are.

In addition to a storm surge and winds, the National Hurricane Center says:

"Life-threatening freshwater flooding is likely from a prolonged and exceptionally heavy rainfall event, which may extend inland over the Carolinas and Mid Atlantic for hundreds of miles as Florence is expected to slow down as it approaches the coast and moves inland."

Enlarge this image toggle caption Western Pacific Hurricane Center Western Pacific Hurricane Center

Florence is one of three hurricanes in the Atlantic Ocean, along with Helene and Isaac. Of the two other storms, which remain far from land, Isaac poses the most immediate risk. With winds of 75 mph, it's expected to strengthen a bit before weakening as it approaches the Lesser Antilles on Thursday.

Dangerous storms are also threatening parts of the U.S. in the Pacific Ocean. Most of the state of Hawaii was under either a tropical storm warning or watch on Monday morning, as Hurricane Olivia bears westward, with 85 mph winds.

Olivia could weaken into a strong tropical storm within 48 hours, according to the Central Pacific Hurricane Center in Honolulu. But forecasters say residents should still beware of the chance for dangerous flooding and wind.

In Guam, Typhoon Mangkhut — a Category 4 storm — narrowly missed dealing a direct blow to the island.