The 2004 Pacific hurricane season consisted of the events that occurred in the annual cycle of tropical cyclone formation over the Pacific Ocean north of the equator and east of the International Date Line. The official bounds of each Pacific hurricane season are dates that conventionally delineate the period each year during which tropical cyclones tend to form in the basin according to the National Hurricane Center (NHC), beginning on May 15 in the Eastern Pacific proper (east of 140°W) and June 1 in the Central Pacific (140°W to the International Date Line), and ending on November 30 in both areas. However, tropical cyclogenesis is possible at any time of year. The first tropical cyclone of the season, Tropical Storm Agatha, developed on May 22; the final, Tropical Depression , dissipated on October 26.

Activity during the 2004 season was below average. A total of seventeen tropical depressions formed, with twelve going on to become named tropical storms. Six storms became hurricanes, of which three further intensified into major hurricanes. Persisting throughout the season was an area of atmospheric and oceanic conditions hostile to tropical cyclones, including below-average sea surface temperatures and a stable air mass. A strong ridge over Mexico frequently steered systems toward this area, limiting their development. The season's general lack of activity was reflected by an overall Accumulated Cyclone Energy index of 71.1 units, which is the seventh-lowest value on record for a Pacific hurricane season as of December 2024.

Impacts on land were unusually light during the season, largely on account of the aforementioned ridge steering the vast majority of tropical cyclones out to sea. No systems caused any confirmed fatalities, although Hurricane Javier in September caused three fishermen to go missing off the coast of Oaxaca. Javier and made landfall as tropical depressions in northwestern Mexico, where they caused minor flooding; also generated locally strong winds and a possible tornado. The remnants of both systems produced heavy rainfall in portions of the western United States. Hurricane Howard in early September washed out roads in western portions of the Baja California peninsula and prompted water rescues in California due to high surf. In mid-October, Tropical Storm Lester caused rainfall of up to in southern Mexico when it passed close to the coast.

Prior to 2015, two time zones were utilized in the Eastern Pacific basin: Pacific east of 140°W, and Hawaii−Aleutian from 140°W to the International Date Line. For convenience, each event is listed in Coordinated Universal Time (UTC) first, using the 24-hour clock (where 00:00 = midnight UTC), with the respective local time included in parentheses. Figures for maximum sustained winds and position estimates are rounded to the nearest five units (knots, miles, or kilometers) and averaged over one minute, 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. This timeline documents the formation of tropical cyclones as well as the strengthening, weakening, landfalls, extratropical transitions, and dissipations during the season. It also includes information that was not released while the storm was active, meaning that data from post-storm reviews by the National Hurricane Center and the Central Pacific Hurricane Center is included.

Timeline of events

May

May 15 The 2004 Eastern Pacific hurricane season officially begins.

May 22 00:00 UTC (5:00 p.m. PDT, May 21) at Tropical Depression forms from an area of unsettled weather about 585 mi (945 km) south-southeast of Cabo San Lucas, Baja California Sur. 12:00 UTC (5:00 a.m. PDT) at Tropical Depression strengthens into Tropical Storm Agatha about 480 mi (770 km) south of Cabo San Lucas, Baja California Sur.

May 23 00:00 UTC (5:00 p.m. PDT, May 22) at Tropical Storm Agatha attains peak winds of 60 mph (95 km/h) and a minimum barometric pressure of about 395 mi (640 km) south of Cabo San Lucas, Baja California Sur.

May 24 00:00 UTC (5:00 p.m. PDT, May 23) at Tropical Storm Agatha weakens into a tropical depression about 305 mi (490 km) south of Cabo San Lucas, Baja California Sur. 12:00 UTC (5:00 a.m. PDT) at Tropical Depression Agatha degenerates into a remnant low about 280 mi (455 km) south of Cabo San Lucas, Baja California Sur.

June No tropical cyclones were active in June. June 1 The 2004 Central Pacific hurricane season officially begins.

July

July 2 12:00 UTC (5:00 a.m. PDT) at Tropical Depression forms from a tropical wave about 760 mi (1,225 km) southwest of the southern tip of the Baja California peninsula.

July 3 00:00 UTC (5:00 p.m. PDT, July 2) at Tropical Depression attains peak winds of 35 mph (55 km/h) and a minimum barometric pressure of about 805 mi (1,295 km) west-southwest of the southern tip of the Baja California peninsula.

July 4 00:00 UTC (5:00 p.m. PDT, July 3) at Tropical Depression degenerates into a remnant low about 1,040 mi (1,675 km) west-southwest of the southern tip of the Baja California peninsula. 00:00 UTC (2:00 p.m. HST, July 3) at Tropical Depression forms from an Intertropical Convergence Zone (ITCZ) disturbance about 1,130 mi (1,815 km) southeast of Johnston Atoll. 18:00 UTC (8:00 a.m. HST) at Tropical Depression attains a minimum barometric pressure of about 835 mi (1,345 km) southeast of Johnston Atoll.

July 5 00:00 UTC (2:00 p.m. HST, July 4) at Tropical Depression attains peak winds of 30 mph (45 km/h) about 760 mi (1,225 km) south-southeast of Johnston Atoll.

July 6 00:00 UTC (2:00 p.m. HST, July 5) at Tropical Depression is last noted as a tropical cyclone about 680 mi (1,095 km) south of Johnston Atoll; it dissipates shortly thereafter.

July 12 12:00 UTC (5:00 a.m. PDT) at A tropical depression forms from a tropical wave about 640 mi (1,030 km) south-southeast of Cabo San Lucas, Baja California Sur. 18:00 UTC (11:00 a.m. PDT) at The tropical depression strengthens into Tropical Storm Blas about 545 mi (880 km) south-southeast of Cabo San Lucas, Baja California Sur.

July 13 12:00 UTC (5:00 a.m. PDT) at Tropical Storm Blas attains peak winds of 65 mph (100 km/h) and a minimum barometric pressure of about 315 mi (510 km) south of Cabo San Lucas, Baja California Sur.

July 14 18:00 UTC (11:00 a.m. PDT) at Tropical Storm Blas weakens into a tropical depression about 505 mi (815 km) west of Cabo San Lucas, Baja California Sur.

July 15 06:00 UTC (11:00 p.m. PDT, July 14) at Tropical Depression Blas degenerates into a remnant low about 660 mi (1,065 km) west of Cabo San Lucas, Baja California Sur.

July 19 00:00 UTC (5:00 p.m. PDT, July 18) at A tropical depression forms from a tropical wave about 620 mi (1,000 km) south-southwest of the southern tip of the Baja California peninsula. 12:00 UTC (5:00 a.m. PDT) at The tropical depression strengthens into Tropical Storm Celia about 650 mi (1,045 km) south-southwest of the southern tip of the Baja California peninsula.

July 22 00:00 UTC (5:00 p.m. PDT, July 21) at Tropical Storm Celia strengthens into a Category 1 hurricane about 850 mi (1,370 km) west-southwest of the southern tip of the Baja California peninsula. 06:00 UTC (11:00 p.m. PDT, July 21) at Hurricane Celia attains peak winds of 85 mph (140 km/h) and a minimum barometric pressure of about 875 mi (1,410 km) west-southwest of the southern tip of the Baja California peninsula. 18:00 UTC (11:00 a.m. PDT) at Hurricane Celia weakens into a tropical storm about 960 mi (1,545 km) west-southwest of the southern tip of the Baja California peninsula.

July 24 12:00 UTC (5:00 a.m. PDT) at Tropical Storm Celia weakens into a tropical depression about 1,260 mi (2,030 km) west-southwest of the southern tip of the Baja California peninsula.

July 26 00:00 UTC (5:00 p.m. PDT, July 25) at Tropical Depression Celia degenerates into a remnant low about 1,645 mi (2,650 km) west of the southern tip of the Baja California peninsula. 12:00 UTC (5:00 a.m. PDT) at Tropical Depression forms from a tropical wave about 760 mi (1,225 km) south-southwest of Cabo San Lucas, Baja California Sur.

July 27 00:00 UTC (5:00 p.m. PDT, July 26) at Tropical Depression strengthens into Tropical Storm Darby about 805 mi (1,295 km) south-southwest of Cabo San Lucas, Baja California Sur.

July 28 00:00 UTC (5:00 p.m. PDT, July 27) at Tropical Storm Darby strengthens into a Category 1 hurricane about 915 mi (1,475 km) southwest of Cabo San Lucas, Baja California Sur. 18:00 UTC (11:00 a.m. PDT) at Hurricane Darby strengthens to Category 2 intensity about 1,035 mi (1,670 km) west-southwest of Cabo San Lucas, Baja California Sur.

July 29 06:00 UTC (11:00 p.m. PDT, July 28) at Hurricane Darby strengthens to Category 3 intensity about 1,135 mi (1,825 km) west-southwest of Cabo San Lucas, Baja California Sur. This makes it the first Pacific major hurricane since Hurricane Kenna in 2002. It simultaneously attains peak winds of 120 mph (195 km/h) and a minimum barometric pressure of . 18:00 UTC (11:00 a.m. PDT) at Hurricane Darby weakens to Category 2 intensity about 1,230 mi (1,985 km) west-southwest of Cabo San Lucas, Baja California Sur.

July 30 00:00 UTC (5:00 p.m. PDT, July 29) at Hurricane Darby weakens to Category 1 intensity about 1,290 mi (2,075 km) west-southwest of Cabo San Lucas, Baja California Sur. 12:00 UTC (5:00 a.m. PDT) at Hurricane Darby weakens into a tropical storm about 1,440 mi (2,315 km) west-southwest of Cabo San Lucas, Baja California Sur.

July 31 12:00 UTC (5:00 a.m. PDT) at Tropical Storm Darby weakens into a tropical depression about 1,785 mi (2,870 km) west of Cabo San Lucas, Baja California Sur.

August

August 1 00:00 UTC (2:00 p.m. HST, July 31) at Tropical Depression Darby crosses 140°W, leaving the jurisdiction of the National Hurricane Center (NHC) and entering the Central Pacific Hurricane Center's (CPHC) area of responsibility. 06:00 UTC (11:00 p.m. PDT, July 31) at Tropical Depression forms about 1,285 mi (2,065 km) southwest of Cabo San Lucas, Baja California Sur. It simultaneously attains peak winds of 30 mph (45 km/h) and a minimum barometric pressure of . 12:00 UTC (2:00 a.m. HST) at Tropical Depression Darby degenerates into a remnant low about 920 mi (1,480 km) east of Honolulu, Hawaii.

August 2 00:00 UTC (5:00 p.m. PDT, August 1) at Tropical Depression is last noted as a tropical cyclone about 1,395 mi (2,240 km) southwest of Cabo San Lucas, Baja California Sur; it dissipates six hours later.

August 19 06:00 UTC (11:00 p.m. PDT, August 18) at A tropical depression forms from an area of unsettled weather about 1,645 mi (2,650 km) east-southeast of Hilo, Hawaii.

August 20

06:00 UTC (11:00 p.m. PDT, August 19) at The aforementioned tropical depression strengthens into Tropical Storm Estelle about 1,310 mi (2,115 km) east-southeast of Hilo, Hawaii.

August 21 06:00 UTC (8:00 p.m. HST, August 20) at Tropical Storm Estelle crosses 140°W, leaving the jurisdiction of the NHC and entering the CPHC's area of responsibility. 12:00 UTC (2:00 a.m. HST) at Tropical Storm Estelle attains peak winds of 70 mph (110 km/h) and a minimum barometric pressure of about 995 mi (1,605 km) east-southeast of Hilo, Hawaii.

August 23 00:00 UTC (2:00 p.m. HST, August 22) at Tropical Storm Estelle weakens into a tropical depression about 800 mi (1,290 km) east-southeast of Hilo, Hawaii. 06:00 UTC (11:00 p.m. PDT, August 22) at A tropical depression forms from the remnants of Atlantic Tropical Storm Earl about 425 mi (685 km) south of Cabo San Lucas, Baja California Sur. 12:00 UTC (5:00 a.m. PDT) at The tropical depression strengthens into Tropical Storm Frank about 390 mi (630 km) south of Cabo San Lucas, Baja California Sur.