 A tropical wave moved off the coast of Africa on July 7 . The wave moved west , but it was not until it moved across the Caribbean Sea that the wave 's convection organized . The system entered into the northeastern Pacific Ocean with concentrated convection and a surface center of circulation while southeast of Acapulco . Moving west @-@ northwest , Tropical Depression Ten @-@ E formed on July 20 393 mi ( <unk> km ) south of Puerto <unk> , Mexico . Early on the following day , the depression strengthened into Tropical Storm Iselle . The storm continued strengthening while in the proximity of Hurricane Hernan , becoming a hurricane on July 22 . 
