Weak wind shear allowed Javier to reach hurricane strength on September 12. Then the storm moved slowly to the west and northwest around a subtropical ridge that was centered over Mexico. Javier then underwent rapid intensification as the storm reached a peak intensity of 150 mph (240 km/h) and a central pressure of 930 millibars. These numbers qualified it as a Category 4 hurricane on the Saffir-Simpson Hurricane Scale and made it the strongest tropical cyclone of the 2004 Pacific hurricane season.