The 2018 Pacific hurricane season produced the highest accumulated cyclone energy value on record in the basin. With 23 named storms, it was the fourth-most active season on record, tied with 1982. The season also featured seven landfalls (Bud, Olivia, Nineteen-E, Rosa, Sergio, Vicente, and Willa), 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.
The second named storm of the season, Hurricane Bud, struck Baja California Sur in mid-June, causing minor damage. Tropical Storm Carlotta stalled offshore of the Mexican coastline, where it also caused minor damage. In early August, Hurricane Hector became one of the few tropical cyclones to cross into the Western Pacific from the Eastern Pacific, while also affecting Hawaii. A few weeks later, Hurricane Lane obtained Category 5 intensity while also becoming Hawaii's wettest tropical cyclone on record, and the second wettest tropical cyclone in US history, only behind Hurricane Harvey of the previous year.
Hurricane Olivia also struck Hawaii, resulting in slight damage. In late September, Hurricanes Rosa and Sergio formed, both of which eventually brought thunderstorms and flash flooding to the Baja California Peninsula and the Southwestern United States. Meanwhile, Hurricane Walaka attained Category 5 intensity before causing disruptions in the Northwestern Hawaiian Islands. In late October, Hurricane Willa became the record-tying third Category 5 hurricane of the season (tied with the 1994 and 2002 seasons) before striking Sinaloa as a major hurricane. Damage across the basin reached $1.25 billion (2018 USD), while 52 people were killed by the various storms.
On May 24, 2018, the National Oceanic and Atmospheric Administration released its annual forecast, predicting an 80% chance of a near- to above-average season in both the Eastern and Central Pacific basins, with a total of 14–20 named storms, 7–12 hurricanes, and 3–7 major hurricanes. The reason for their outlook was the possible development of an El Niño, which reduces vertical wind shear across the basin and increases sea surface temperatures. In addition, many global computer models expected a positive Pacific decadal oscillation (PDO), a phase of a multi-decade cycle that favored much warmer than average sea surface temperatures that had been ongoing since 2014 to continue, in contrast to the 1995–2013 period, which featured below normal activity. On May 25, the Servicio Meteorológico Nacional (SMN) issued its first forecast for the season, predicting a total of 18 named storms, 6 hurricanes, and 4 major hurricanes to develop.