The 2018 Pacific hurricane season was one of the most active Pacific hurricane seasons on record, producing the highest accumulated cyclone energy value on record in the basin. The season had the fourth-highest number of named storms – 23, tied with 1982. The season also featured eight landfalls, six of which occurred in Mexico. The season officially began on May 15 in the Eastern Pacific, and on June 1 in the Central Pacific; they both ended on November 30. These dates conventionally delimit the period of each year when most tropical cyclones form in the Pacific basin. However, tropical cyclone formation is possible at any time of the year, as illustrated when the first tropical depression formed on May 10, five days prior to the official start of the season.

Hurricane Rosa brought widespread flooding to northwestern Mexico and the Southwestern United States in late September 2018, and was the first tropical cyclone to make landfall in Baja California since Nora in 1997. The seventeenth named storm, tenth hurricane, and seventh major hurricane of the 2018 Pacific hurricane season; Rosa originated from an Atlantic tropical wave that crossed the West African coast on September 6. The wave proceeded westward across the Atlantic, traversing Central America before entering the Gulf of Tehuantepec on September 22. There, the weather system acquired cyclonic features and became a tropical storm on September 25. Within a favorable atmosphere, Rosa entered a period of rapid intensification on September 27, peaking as a Category 4 hurricane with maximum sustained winds of 150 mph (240 km/h) a day later. Over the next few days, Rosa turned north and then northeast while steadily weakening, making landfall in Baja California as a tropical depression on October 2. After crossing over into the Gulf of California, the remnant system split apart and merged with an upper-level low off the coast of California by October 3.