The 2015 Pacific hurricane season is the second-most active Pacific hurricane season on record, with 26 named storms, only behind the 1992 season. A record-tying 16 of those storms became hurricanes, and a record 11 storms further intensified into major hurricanes throughout the season. The Central Pacific, the portion of the Northeast Pacific Ocean between the International Date Line and the 140th meridian west, had its most active year on record, with 16 tropical cyclones forming in or entering the basin. Moreover, the season was the third-most active season in terms of accumulated cyclone energy, amassing a total of 290 units. The season officially started 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 Northeast Pacific basin. However, the formation of tropical cyclones is possible at any time of the year. This was shown when a tropical depression formed on December 31. The above-average activity during the season was attributed in part to the very strong 2014–2016 El Niño event.

A Pacific hurricane is a tropical cyclone that develops within the northeastern and central Pacific Ocean to the east of 180°W, north of the equator. For tropical cyclone warning purposes, the northern Pacific is divided into three regions: the eastern, central, and western, while the southern Pacific is divided into 2 sections, the Australian region and the southern Pacific basin between 160°E and 120°W. Identical phenomena in the western north Pacific are called typhoons. This separation between the two basins has a practical convenience, however, as tropical cyclones rarely form in the central north Pacific due to high vertical wind shear, and few cross the dateline.