Arthur has strengthened to a hurricane in the Atlantic, where it threatens to deliver the Carolinas a glancing blow on Independence Day.

The hurricane's maximum sustained winds early Thursday are near 75 mph with some additional strengthening expected.

Hurricane warnings on the coast of North Carolina have been extended and now cover an area from Surf City to the Virginia border.

Hurricane Arthur is centered about 340 miles southwest of Cape Hatteras, North Carolina, and is moving north near 9 mph.

The first named storm of the Atlantic hurricane season has prompted a mandatory evacuation for visitors to the Outer Banks' Hatteras Island as of 5 a.m. Thursday. Residents also are advised to leave the island.

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