Gustav moved erratically to the west-northwest toward the North Carolina-South Carolina border over the next two days, it slowly strengthened, acquiring more tropical characteristics. On September 10, a poorly organized band of stronger winds developed around the center, and Gustav was designated a fully tropical storm shortly before turning toward the north and brushing Cape Hatteras, then accelerating toward the northeast and away from the coast. On September 11, while under the influence of a non-tropical system over New England, Gustav quickly strengthened into a hurricane, in a process similar to the intensification of Hurricane Michael in 2000. Gustav reached its peak intensity of 100 mph (160 km/h) later that day.