Hurricane Isabel was the costliest and deadliest hurricane in the 2003 Atlantic hurricane season. It was the ninth named storm, fifth hurricane, and second major hurricane of the season. Isabel formed from a tropical wave in the tropical Atlantic Ocean. It moved northwestward, and it steadily strengthened to reach peak winds of 165 mph (265 km/h) on September 11. After weakening and strengthening for four days, Isabel slowly weakened. It moved onto the Outer Banks of North Carolina with winds of 105 mph (165 km/h) on September 18. It quickly weakened over land.