At 1500 UTC on September 11, a navy aircraft first penetrated the storm; in less than 24 hours, the storm rapidly strengthened into the equivalence of a Category 1 hurricane on the Saffir–Simpson Hurricane Scale, and shortly afterward attained peak winds of 100 mph , roughly 18 hours after being classified a tropical storm, as another aircraft registered a barometric pressure of 977 mb (28.84 inHg), a drop of 22 mb in 24 hours.