The cyclone gradually intensified until September 5 , when it underwent rapid deepening and reached Category 4 status on the Saffir-Simpson Hurricane Scale ; at the time Ivan was the southernmost major North Atlantic hurricane on record .
The cyclone slowly intensified until September 5 , when it underwent rapid deepening and reached Category 4 status on the Saffir-Simpson Hurricane Scale ; at the time Ivan was the southernmost major hurricane on record .