 Hurricane Isabel was the costliest , deadliest , and strongest hurricane in the 2003 Atlantic hurricane season . The ninth named storm , fifth hurricane , and second major hurricane of the season , Isabel formed near the Cape Verde Islands from a tropical wave on September 6 in the tropical Atlantic Ocean . It moved northwestward , and within an environment of light wind shear and warm waters it steadily strengthened to reach peak winds of 165 mph ( 265 km / h ) on September 11 . After fluctuating in intensity for four days , Isabel gradually weakened and made landfall on the Outer Banks of North Carolina with winds of 105 mph ( 165 km / h ) on September 18 . It quickly weakened over land and became extratropical over western Pennsylvania the next day . 
