The 2004 Pacific hurricane season was an overall below-average Pacific hurricane season in which there were 12 named tropical storms, all of which formed in the eastern Pacific basin. Of these, 6 became hurricanes, and 3 of those intensified into major hurricanes. No storms made landfall in 2004, the first such occurrence since 1991. In addition to the season's 12 named storms, there were five tropical depressions that did not reach tropical storm status. One of them, Sixteen-E, made landfall in northwestern Sinaloa. The season officially began on May 15 in the eastern Pacific, and on June 1 in the central Pacific basin. It officially ended in both basins on November 30. These dates conventionally delimit the period during each year when most tropical cyclones form in each respective basin. These dates conventionally delimit the period during each year when a majority of tropical cyclones form. The season was reflected by an accumulated cyclone energy (ACE) index of 71 units.

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.