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 (east of 140°W and north of the equator). 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 (between140°W and the International Date Line, north of the equator). 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. The lack of notable activity was brought on due to the presence of a Modoki El Niño - a rare type of El Niño in which unfavorable conditions exist in the Pacific basin due to the normally warmer-than-average waters shifting further westward.

Impact throughout the season was minimal and no deaths were recorded. In early August, the remnants of Hurricane Darby contributed to localized heavy rainfall in Hawaii, causing minor street and stream flooding; coffee and macadamia trees were damaged as well. In early September, Hurricane Howard resulted in significant flooding across the Baja California peninsula that damaged agricultural land and 393 homes. Large swells also resulted in about 1,000 lifeguard rescues in California. In mid-September, Javier, the strongest hurricane of the season, caused three fishermen to go missing and helped alleviate a multi-year drought across the Southwest United States. It produced record rainfall in the state of Wyoming. In mid- to late October, Tropical Storm Lester and Tropical Depression Sixteen-E each dumped heavy rain upon parts of Mexico, resulting in minor flood and mudslide damage.

Seasonal forecasts +Predictions of tropical activity in the 2004 seasonSourceDateNamedstormsHurricanesMajorhurricanesRefAverage (1966–2003)1693Record high activity2716 (tie)11Record low activity8 (tie)30† (tie)SMNJanuary 20041563SMNMay 17, 20041472NOAAMay 21, 200413–156-82-4SMNAugust 20041363Actual activity 1263 In January 2004, the Servicio Meteorológico Nacional (SMN) released their first prediction for tropical cyclone activity throughout the Northeast Pacific. Based on a Neutral El Niño Southern Oscillation (ENSO), a total of 15 named storms, 6 hurricanes, and 3 major hurricanes was forecast. These values were slightly altered in May to 14 named storms, 7 hurricanes, and 2 major hurricanes, and again in August to 13 named storms, 6 hurricanes, and 3 major hurricanes.

On May 17, the National Oceanic and Atmospheric Administration issued its seasonal forecast for the 2004 central Pacific season, predicting four or five tropical cyclones to form or cross into the basin. Likewise to the SMN, near average activity was expected largely as a result of a Neutral ENSO. The organization issued its experimental eastern Pacific outlook on May 21, highlighting a 45 percent change of below-average activity, 45 percent chance of near-average activity, and only a 10 percent chance of above-average activity in the basin. A total of 13 to 15 named storms, 6 to 8 hurricanes, and 2 to 4 major hurricanes was forecast.

Seasonal summary

Activity was below average throughout the season. Altogether there were 12 named storms, 6 of which became hurricanes, and 3 of those intensified into major hurricanes, compared to the long-term average of 16 named storms, 9 hurricanes, and 3 major hurricanes.

The season's first storm, Agatha, developed on May 22. No tropical cyclones developed during June, below the average of 2 named storms and 1 hurricane, and also the first time since 1969 that the month was cyclone-free. The first hurricane of the season was Celia, which briefly reached Category 1 strength on July 22. It was soon followed by Darby, the first major Hurricane of the season and the first in the Eastern Pacific since Kenna in 2002. Later, on September 14, Javier attained sustained winds of , making it the strongest hurricane of the season.

Overall wind energy output was reflected with an ACE index value of 71 units for the season. Although vertical wind shear was near average and ocean temperatures were slightly warmer than average south of Mexico, anomalously cool waters and drier than average air mass existed in the central portions of the eastern Pacific. Anomalously strong mid-level ridging extending from the Atlantic to northern Mexico steered a majority of the season's cyclones toward this inhospitable region and also acted to steer all the system of tropical storm intensity or stronger away from land.

Systems Tropical Storm Agatha

A nearly stationary trough stretched from the eastern Pacific into the eastern Caribbean Sea during mid-May. An ill-defined tropical wave crossed Central America on May 17 and interacted with the trough, eventually leading to the formation of a tropical depression at 00:00 UTC on May 22. The newly formed cyclone moved northwest parallel to the coastline of Mexico while steadily organizing in a low wind shear regime, intensifying into Tropical Storm Agatha by 12:00 UTC that day and attaining peak winds of twelve hours later. Increasingly cool ocean temperatures and a drier air mass caused Agatha to weaken quickly thereafter, and it degenerated into a remnant low by 12:00 UTC on May 24. The post-tropical cyclone drifted aimlessly before dissipating well south of the Baja California Peninsula on May 26.

Tropical Depression Two-E

A westward-moving tropical wave from Africa crossed Central America into the eastern Pacific in late June, coalescing into a tropical depression at 12:00 UTC on July 2 well southwest of the southern tip of the Baja California Peninsula. Steered westward by low-level flow, the depression failed to organize amid wind shear and cooler sea surface temperatures, instead degenerating into a remnant low at 00:00 UTC on July 4. The post-tropical cyclone dissipated a day later.

Tropical Depression One-C

An organized region of convection within the Intertropical Convergence Zone developed into a tropical depression at 03:00 UTC on July 5 while located roughly south-southeast of Johnston Atoll, becoming the farthest-south-forming central Pacific tropical cyclone since Tropical Storm Hali (1992). Steered westward, the depression failed to intensify due to its quick forward motion despite a seemingly favorable environment, and it quickly dissipated at 00:00 UTC on July 6.

Tropical Storm Blas

A tropical wave crossed Central America on July 8, developing into a tropical depression at 12:00 UTC on July 12 while located about southwest of Zihuatanejo, Mexico; six hours later, the depression intensified into Tropical Storm Blas. Steered swiftly northwestward around a mid-level ridge over the southwestern United States, the cyclone steadily intensified and reached peak winds of early on July 13 as a large and robust convective canopy became evident. Blas began a steady weakening trend as it tracked over increasingly cool sea surface temperatures, weakening to a tropical depression at 18:00 UTC on July 14 and degenerating into a large remnant low twelve hours later. The post-tropical cyclone decelerated and curved northeastward, dissipating well west of central Baja California early on July 19.

Hurricane Celia

A vigorous tropical wave entered the East Pacific on July 13, acquiring sufficient organization to be declared a tropical depression at 00:00 UTC on July 19 while located about south-southwest of the southern tip of the Baja California Peninsula. Directed west-northwest around a subtropical ridge, the cyclone steadily intensified amongst a favorable environment, becoming Tropical Storm Celia at 12:00 UTC that same day and further strengthening into a Category 1 hurricane on the Saffir–Simpson hurricane wind scale, the season's first, at 00:00 UTC on July 22. After attaining peak winds of six hours later, an increasingly unfavorable environment began to hinder the system. Celia weakened to a tropical storm at 18:00 UTC on July 22 and eventually degenerated into a remnant low at 00:00 UTC on July 26. The post-tropical cyclone dissipated about west-southwest of the southern tip of the Baja California Peninsula later that morning.

Hurricane Darby

A tropical depression formed at 12:00 UTC on July 26 while positioned about south-southwest of Cabo San Lucas, Mexico from a tropical wave that entered the eastern Pacific nearly a week prior. The system quickly intensified as it curved west-northwest around a subtropical ridge, becoming Tropical Storm Darby at 00:00 UTC on July 27 and strengthening into a Category 1 hurricane early the next day. After attaining its peak as the season's first major hurricane with winds of , increasing wind shear and cooler sea surface temperatures begin to weaken the cyclone. It weakened to a tropical storm at 12:00 UTC on July 30 and further to a tropical depression a day later as it entered the jurisdiction of the Central Pacific Hurricane Center. At 12:00 UTC on August 1, Darby dissipated about east of the Hawaiian Islands.

Although Darby produced no impacts to land as a tropical cyclone, its remnant moisture field combined with an upper-level trough over Hawaii to produce an unstable atmosphere. General rainfall amounts of were recorded across the Big Island and Oahu, with a localized peak of in Kaneohe; this led to flooding and several road closures. Minor stream flooding was observed on the southeast flank of Mount Haleakalā. A rainfall total of was recorded at the Honolulu International Airport, contributing to the wettest August on record in the city. Some coffee and macadamia nut trees were damaged.

Tropical Depression Six-E

Operationally, an area of disturbed weather was thought to have coalesced into a tropical depression at 09:00 UTC on July 29 while located well southwest of the Baja California Peninsula. The depression was only expected to intensify slightly before entering cooler waters and interacting with outflow from nearby Hurricane Darby. By late that evening, however, its presentation on satellite imagery more resembled a trough, and the NHC discontinued advisories. In post-season analysis, the organization determined that the depression did not form until 06:00 UTC on August 1 but lasted 24 hours.

Tropical Storm Estelle

A tropical wave interacted with a disturbance embedded in the ITCZ in mid-August, leading to the designation of a tropical depression at 06:00 UTC on August 19 while located east-southeast of Hilo, Hawaii. The cyclone moved west-northwest following formation, steered around a subtropical ridge. It intensified into Tropical Storm Estelle at 06:00 UTC on August 20 and attained peak winds of at 12:00 UTC the next morning as it crossed into the central Pacific. Thereafter, increasing wind shear caused Estelle to a steady weakening trend. At 00:00 UTC on August 23, the cyclone decelerated to a tropical depression while turning west-southwest, and at 18:00 UTC the following day, it further degenerated into a remnant low. The post-tropical cyclone continued on a west-southwest trajectory prior to dissipating south-southeast of the Big Island at 00:00 UTC on August 26.

Hurricane Frank