subsequent to developing, deep convection began developing and increasing around the center. on september 11, an advanced microwave sounding unit temperature cross-section analysis indicated the system developed a warm thermal core; as a result, it was re-classified as tropical depression ten. convection continued increasing, and it intensified to tropical storm status by 1200 utc. operationally, it was considered a tropical depression, and significant strengthening was not expected. however, reports from hurricane hunters confirmed the presence of tropical storm force winds, and as a result the national hurricane center named the cyclone "florence". the storm continued quickly intensifying, and with the hurricane hunters reporting flight-level winds of over 85 mph (140 km/h), it was estimated florence attained hurricane status late on september 11, or just six hours after the national hurricane center began issuing advisories on the storm. the strongest winds were confined to a very small area near the edge of the convection. initially, the hurricane was tracking west-southwestward, steered by a mid-level ridge to its northwest.