 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 Pennsylvania the next day.