Timeline of the 2015 Pacific hurricane season

The 2015 Pacific hurricane season was the second-most active Pacific hurricane season on record, and featured the strongest tropical cyclone ever observed in the Western Hemisphere: Hurricane Patricia. The season officially started on May 15 in the Eastern Pacific—east of 140°W—and on June 1 in the Central Pacific—between the International Date Line and 140°W—and ended on November 30. These dates typically cover the period of each year when most tropical cyclones form in the Northeastern Pacific tropical cyclone basin. The season's first storm, Hurricane Andres, developed on May 28; the season's final storm, Tropical Depression Nine-C, dissipated on December 31, well after the official end of the season.

Throughout the season, 31 tropical depressions developed, 26 of which became tropical storms, a record-tying 16 of them reached hurricane strength, and a record-breaking 11 achieved major hurricane intensity. Activity in the Central Pacific shattered records, with 16 tropical cyclones forming in or entering the basin; the previous highest was 11 during the 1992 and 1994 seasons. On August 30, three hurricanes at Category 4 strength—Ignacio, Jimena, and Kilo—existed simultaneously in the Northeastern Pacific, which was a first for the basin. On October 23, Hurricane Patricia became the strongest hurricane ever recorded in the Western Hemisphere, with a minimum atmospheric pressure of 872 mbar (hPa; 25.75 inHg) and maximum sustained winds of 215 mph (345 km/h). Activity in the basin was boosted by the strong 2014–16 El Niño event, which brought anomalously high sea surface temperatures and low vertical wind shear that helped the numerous systems form and intensify.

This timeline documents tropical cyclone formations, strengthening, weakening, landfalls, extratropical transitions, and dissipations during the season. It includes information that was not released throughout the season, meaning that data from post-storm reviews by the National Hurricane Center, such as a storm that was not initially warned upon, has been included.

The time stamp for each event is first stated using Coordinated Universal Time (UTC), the 24-hour clock where 00:00 = midnight UTC. The NHC uses both UTC and the time zone where the center of the tropical cyclone is currently located. The time zones utilized (east to west) are: Central, Mountain, Pacific and Hawaii. In this timeline, the respective area time is included in parentheses. Additionally, figures for maximum sustained winds and position estimates are rounded to the nearest 5 units (miles, or kilometers), following National Hurricane Center practice. Direct wind observations are rounded to the nearest whole number. Atmospheric pressures are listed to the nearest millibar and nearest hundredth of an inch of mercury.