The depression initially tracked slowly north-northwestward and gradually strengthened. Late on September 1 it intensified into Tropical Storm Isis while located about 200 miles (320 km) south of Cabo San Lucas. Upon becoming a tropical storm, the deep convection was not organized, causing one forecaster to describe Isis as a large monsoon-like system. A mid-level trough extending southward from the Arizona/California border caused the storm to accelerate northward. The storm quickly strengthened; six hours after Isis became a tropical storm it reached winds of 70 mph (115 km/h). Very deep, symmetrical convection developed over the poorly defined center of circulation while banding features began to form, although ill-defined outflow and land interaction with the Baja California Peninsula initially prevented further strengthening. At 1200 UTC on September 2, Isis made landfall on extreme southeastern Baja California Sur as a strong tropical storm, and subsequently turned to the north-northeast.