 Located within an area of light wind shear and warm waters , Isabel gradually organized as curved bands developed around a circular area of deep convection near the center . It steadily strengthened as it moved to the west @-@ northwest , and Isabel strengthened to a hurricane on September 7 subsequent to the development of a large , yet ragged eye located near the deepest convection . The eye , overall convective pattern , and outflow steadily improved in organization , and deep convection quickly surrounded the 40 @-@ mile ( 60 km ) -wide eye . Isabel intensified on September 8 to reach major hurricane status while located 1 @,@ 300 miles ( 2 @,@ 100 km ) east @-@ northeast of Barbuda . On September 9 , Isabel reached a primary peak intensity of 135 mph ( 215 km / h ) for around 24 hours , a minimal Category 4 hurricane on the Saffir – Simpson Hurricane Scale . 
