The 1978 Pacific hurricane season was the first Pacific hurricane season to use both masculine and feminine names for tropical cyclones. It also began the modern practice of utilizing naming lists every six years. Despite lacking an El Niño, a common driver of enhanced activity in the East and Central Pacific basins, the 1978 season was active. It featured 19 named storms, 14 hurricanes, and 7 major hurricanes, the latter of which are Category 3 or stronger cyclones on the Saffir–Simpson scale. Within the confines of the Central Pacific basin, located between the International Date Line and 140°W, 13 tropical cyclones or their remnants were observed by forecasters at the Central Pacific Hurricane Center, a record number of occurrences at the time. Seasonal activity began on May 30 and ended on October 21, within the limits of a traditional hurricane season which begins on May 15 in the East Pacific and June 1 in the Central Pacific. The season ends on November 30 in both basins. These dates conventionally delimit the period during each year when most tropical cyclones form.

The first system of the season, Aletta, made landfall on the Mexico coastline on May 31. Hurricanes Carlotta, Daniel, and Iva tracked into the Central Pacific as dissipating cyclones, where they produced a few inches of rainfall across the Hawaiian Islands. More substantive impacts came from Hurricane Fico, the longest-lived hurricane and the longest-tracked hurricane on record in the Central Pacific at the time. Large waves and rough seas caused severe damage to beachfront homes and forced the rescuing of stranded boaters offshore. Strong winds damaged trees and caused power outages. Damage across Hawaii totaled $200,000. In early September, the remnants of Hurricane Norman produced accumulating rain and snow across California, resulting in severe damage to its crops that totaled in excess of $300 million, in addition to killing eight people. In mid-October, Susan rapidly developed into a Category 4 hurricane over the Central Pacific, one of the strongest hurricanes on record there at the time. It persisted until October 21, marking an end to seasonal activity.

Systems

Hurricane Aletta

A small tropical disturbance, originating within the Intertropical Convergence Zone (ITCZ) across the Caribbean Sea, developed in the Gulf of Tehuantepec on May 27. The system increased in both size and organization over the coming days, and it was upgraded to Tropical Storm Aletta around 12:00 UTC on May 30. Tracking northwest, the system continued to intensify over warm ocean waters, and an eye became evident on weather satellite. This development coincided with a ship report of winds, and Aletta strengthened into the season's first hurricane by 00:00 UTC on May 31. The system subsequently weakened as it curved north-northwest ahead of an upper-level trough over northwestern Mexico, and it made landfall about west of Zihuatanejo, Guerrero, at 17:30 UTC on May 31. Aletta transitioned to an extratropical cyclone about six hours before it degenerated to a disturbance over southwestern Mexico on June 1.

Tropical Storm Bud

The season's second tropical cyclone began as a disturbance spawned by an African tropical wave southwest of the Mexico coastline on June 15. It moved generally westward over very warm waters, and observations from satellite imagery and ships outlined the formation of a tropical depression by 00:00 UTC on June 17. Six hours later, the depression intensified into Tropical Storm Bud. Continued ship observations relayed Bud's intensification to a cyclone on June 18, but the storm weakened thereafter as it moved west-northwest under the influence of a ridge, and it ultimately dissipated within the ITCZ after 06:00 UTC on June 26 while located over the open Central Pacific.

Hurricane Carlotta

To the east of Tropical Storm Bud, a new tropical disturbance – originating as a Caribbean ITCZ disturbance – was identified south of Acapulco, Guerrero, on June 15. The comparatively small system became a tropical depression around 06:00 UTC on June 17 and Tropical Storm Carlotta eighteen hours later while it moved over warm ocean waters. After formation, Carlotta embarked toward the west-southwest, steered by the same ridge that directed Bud. The storm displayed a small eye in satellite imagery early on June 19, and it was upgraded to a hurricane by 06:00 UTC that day. Carlotta continued to intensify as it curved west-northwest, becoming the season's first major hurricane around 06:00 UTC on June 20 and ultimately peaking as a Category 4 hurricane with winds of by 12:00 UTC on June 21. Carlotta maintained its strength for a time before it encountered cooler waters and dry air on June 23. The cyclone steadily lost strength and degenerated to a disturbance after 18:00 UTC on June 25 but remained a traceable entity as it moved across the Central Pacific. The disturbance moved across the Hawaiian island chain on June 28 and continued west, ultimately merging with a cold-core low after crossing the International Date Line. It was last identified over the West Pacific near Minami-Tori-shima on July 10.

Although wind effects across Hawaii were minimal, the remnants of Carlotta delivered heavy rainfall across much of the Hawaiian island chain. Accumulations exceeded , particularly on Oahu.

Hurricane Daniel

A tropical disturbance, first identified in association with a tropical wave west of Nicaragua on June 24, moved west-northwest and organized into a tropical depression by 18:00 UTC on June 26. It intensified into Tropical Storm Daniel within twelve hours but weakened to a tropical depression again while tracking over ocean waters. After moving into warmer waters again, Daniel regained tropical storm strength before 18:00 UTC on June 28 and intensified into a hurricane 24 hours later. Around 12:00 UTC on June 30, the hurricane attained major hurricane strength with winds of . The cyclone tracked west and then west-southwest over steadily cooler waters, which resulted in its weakening and degeneration to a disturbance after 18:00 UTC on July 3. The remnant system moved across the Central Pacific and through the Hawaiian Islands, where it lost definition on July 11.

As the circulation of Daniel moved over the Hawaiian Islands, it produced rainfall totals of across the Big Island and Maui. Accumulation over windward sections of opposing islands was more isolated and generally confined under .

Tropical Storm Emilia

An area of disturbed weather and associated tropical wave was observed east of Acapulco on July 3. It moved southwest during the early stages of its existence before curving more toward the northwest. Satellite imagery identified the existence of a tropical depression by 18:00 UTC on July 6, and that depression quickly intensified into Tropical Storm Emilia six hours later. The newly named storm gathered strength over subsequent days, attaining peak winds of around 06:00 UTC on July 9. Beyond that time, Emilia crossed into cooler waters and began to rapidly weaken, dissipating after 18:00 UTC on July 10.

Hurricane Fico

Fico, similar to the season's preceding cyclones, began as an area of disturbed weather in association with a tropical wave east of Acapulco. It moved west-northwest over warm waters, becoming a tropical depression around 00:00 UTC on July 9 and intensifying into a tropical storm 24 hours later. Fico continued to rapidly gain strength and became a hurricane around 18:00 UTC on July 10. As it did so, the hurricane was characterized with a well-defined eye and outflow radiating far away from the center. Fico intensified into a major hurricane by 12:00 UTC on July 11 and later peaked as a Category 4 hurricane with winds of a day later. On July 13–14, the cyclone passed over a pocket of ocean waters, which caused it to rapidly weaken to Category 1 intensity. However, underlying waters soon warmed again, allowing Fico to regain Category 4 strength. Fico fluctuated in intensity over many days as it crossed into the Central Pacific basin and passed south of Hawaii. After July 20, the hurricane curved northwest ahead of an upper-level trough, bringing the storm over cooler waters again. The system rapidly weakened, finally dissipating after 18:00 UTC on July 28 after having traveled .

At the time, Fico was the longest-duration hurricane and furthest-traveled hurricane on record in the Central Pacific. It tracked further than any West Pacific typhoon by that point, and only one typhoon – Rita in 1972 – persisted at that intensity longer than Fico. In the Atlantic, only hurricanes Ginger, Carrie, and Faith exceeded Fico with regard to distance traveled or time spent as a hurricane. Fico produced considerable impacts in Hawaii. Southerly flow in association with a cyclone over the Southern Hemisphere combined with east-northeasterly flow from the hurricane, producing beach road flooding along the southeastern shore of the Big Island while Fico was still away. Ocean waves, breaking at at the coast and larger values offshore, caused severe damage to beachfront homes and roads. Similar waves were observed along the coasts of Oahu and Kauai. A sloop became stranded in the cyclone's circulation, forcing a Navy torpedo boat to rescue six people on board. A tugboat was run aground on a reef along the southern shore of Kauai. By July 21, a strong trade wind gradient exacerbated by the presence of Fico caused widespread winds over , which resulted in downed trees and power outages. Overall damage in Hawaii totaled $200,000. A week later, the remnants of the storm became intertwined with a strong frontal system, producing heavy rain and winds up to to the Aleutian Islands.

Hurricane Gilma

An area of disturbed weather spawned by a tropical wave developed southeast of Acapulco on July 11 and rapidly grew in size. It developed into a tropical depression around 00:00 UTC on July 13 and further into Tropical Storm Gilma six hours later while curving from west-southwest to west-northwest. Further organization brought Gilma to hurricane strength around 18:00 UTC on July 15 and major hurricane intensity by 06:00 UTC the next day. By this point, satellite imagery revealed a system with a cloud shield about in diameter and an eye about wide. Immediately after peak, the effects of cold waters and dry air began to affect Gilma, and the storm weakened rapidly. It degenerated to a disturbance after 00:00 UTC on July 20 while located well west of Baja California. Its well-defined circulation tracked north of Hawaii before dissipating on July 27.

Hurricane Hector

The third in a series of major hurricanes began as a tropical disturbance and accompanying tropical wave south of Guatemala on July 19. The system moved west-northwest, becoming a tropical depression around 00:00 UTC on July 22 and Tropical Storm Hector six hours later. Further strengthening brought the system to hurricane strength by 12:00 UTC on July 23, after which time a well-defined eye developed on satellite imagery. Hector became a major hurricane around 00:00 UTC on July 25 before rapidly strengthening to a Category 4 storm with winds of six hours later. The cyclone continued west-northwest into a sharply more hostile environment of cold waters and dry air, causing weakening that resulted in Hector's degeneration to a disturbance after 18:00 UTC on July 29. The remnants of the storm drifted westward and dissipated northeast of Hawaii on August 2.

Hurricane Iva