Tropical Depression Nine-E strengthened into Tropical Storm Hernan on July 21 while 684 mi (1,100 km) south of Cabo San Lucas. The tropical storm continued to strengthen and as it moved to the northwest, and became a hurricane late on July 21. Hernan continued to strengthen and as it passed 145 mi (230 km) southwest of Clarion Island. On July 23, Hernan reached its peak strength of 155 mph (250 km/h) and minimum pressure of as the center of circulation was 207 mi (335 km) south-southwest of Clarion Island. On July 24, concentric eyewalls (one eyewall located inside another) formed around the center of Hernan, which was the first time this pattern had been observed with an eastern Pacific hurricane.