A tropical wave that drifted across the shear-ridden Atlantic emerged into the Pacific Ocean on July 27. It organized into a depression July 30 and was named Tropical Storm Guillermo the next day. It quickly intensified, reaching hurricane status on August 1. Guillermo became a major hurricane August 2. It reached Category 4 intensity on August 3 before weakening slightly and restrengthening. The hurricane attained Category 5 strength August 4. Guillermo's peak intensity was 919 mbar (919 hPa) and .