The 1998 Pacific hurricane season was a fairly average Pacific hurricane season, with 16 total systems forming; despite this, it had nine hurricanes and six major hurricanes, which was well above average. The season officially started on May 15 in the eastern Pacific and on June 1 in the central Pacific, and ended on November 30; these dates conventionally delimit the period during which most tropical cyclones form in that region. The first tropical cyclone developed on June 11, about ten days later than the normal start of the season. The final storm of the year, Hurricane Madeline, dissipated on October 20. Storm activity in the Central Pacific Hurricane Center's warning zone was low, with just one tropical depression observed in the region. Two tropical cyclones from the eastern Pacific (Darby and Estelle) also entered the central Pacific; the former did so as a hurricane.
The most notable tropical cyclone of the year was Hurricane Isis, which killed fourteen people when it made landfall on southern Baja California Sur and coastal Sinaloa in Mexico. Isis caused considerable damage in the nation, destroying more than 700 homes and damaging dozens of cars. It later produced sporadic rainfall in the southwestern United States, leading to some traffic accidents. In addition to Isis, Tropical Storm Javier moved ashore the coast of Jalisco in Mexico; the country also experienced indirect effects from four other storms, all of which remained offshore. One tropical cyclone, Hurricane Lester, affected Central America, causing two deaths in Guatemala, and later brought heavy rains to southern Mexico. Three tropical cyclones brought light to moderate rainfall to the southwestern United States, and one hurricane produced rough surf along the coast of California. Hurricane Madeline contributed to a deadly and costly flood in southern Texas.
Seasonal summary
The season produced 13 named storms, slightly below the average of 15 named storms per season. However, the season total of nine hurricanes was one above the average, and the total of six major hurricanes surpassed the average of three. Activity during the season was hindered by the northward movement of the Intertropical Convergence Zone (ITCZ). The ITCZ, which is normally situated south of the Gulf of Tehuantepec, shifted northward into Central and Southern Mexico, making the cyclone closer to cooler sea surface temperatures, hence limiting the number of storms that formed during the season. Although a semi-permanent anticyclone persisted through the summer of 1998, causing most of the storms to remain at sea, some storm did threaten the Baja California Peninsula due to a weakness in the anticyclone. Except for Hurricane Kay, all of the storms of the season originated from tropical waves. Accumulated Cyclone Energy is, broadly speaking, a measure of the power of a storm multiplied by its duration, so longer-lived hurricanes have higher ACEs. The total ACE for the season was 1,339,700 kt2. Because several storms in 1998 were long-lasting or intense, the season's ACE was near-normal. Hurricane Howard had the highest ACE, measuring 292,700 kt2.
Systems Tropical Storm Agatha
A poorly defined tropical wave crossed Central America into the eastern Pacific Ocean on June 8. As it tracked westward under the influence of a ridge to its north, a broad circulation developed. Gradually, the dominant center of circulation became better defined, with increasingly organized convection and developing banding features. By early on June 11, the center became sufficiently associated with the convection for the National Hurricane Center (NHC) to classify the system as Tropical Depression One-E. This occurred while the area of unsettled weather was about south-southwest of Acapulco, Mexico.
The center of the depression was not initially well defined, with restricted outflow in the eastern half of the circulation. As such, the depression failed to attain any significant organization in the days subsequent to its formation. Later, an approaching tropical wave merged with the depression, resulting in a trend of intensification and increased organization. By June 13, the NHC upgraded the depression to tropical storm status, and gave it the name "Agatha". Agatha was about south-southeast of Cabo San Lucas when it became a tropical storm. As Agatha became a tropical storm, forecasters predicted that it would not strengthen further, due to its forecast track passing over cooler waters. However, Agatha quickly strengthened, developing a curved band of convection wrapping around its center, and early on June 11 it attained a peak intensity of while about southwest of the southern tip of Baja California. Agatha maintained peak winds for about 12 hours before moving over colder waters and gradually weakening. On June 15, it degenerated back into a tropical depression, and a day later, it dissipated over the open waters of the Pacific Ocean.
Tropical Depression Two-E
A few days later, another westward-moving tropical disturbance paralleled the southern coast of Central America and Mexico. Convection in the area organized steadily, and late on June 19, the system developed into Tropical Depression Two-E about south-southwest of Manzanillo, Mexico. On becoming a tropical depression, the system maintained a large, elongated, low-level circulation with some banding features and restricted outflow due to wind shear. The National Hurricane Center first predicted that the depression would intensify, reaching winds of , though two computer models projected it to quickly dissipate. Under the influence of a ridge over Mexico, the depression moved to the west-northwest, and, under the influence of increasing wind shear, the depression failed to organize significantly. By June 20, the circulation center was partially exposed, and was located to the northeast of the primary convection – traits that signal a weak storm. Two-E approached tropical storm status, though deep convection waned after the system moved over cooler waters. On June 21, the National Hurricane Center issued the last advisory on the depression, stating that the depression maintained a very well-defined, low-level circulation, but had no convection associated with the system. Locally heavy rains fell across southwest Mexico in association with this system, peaking at at Las Gaviotas/Compostela.
Hurricane Blas
On June 8, a tropical wave emerged off the coast of Africa. The wave remained weak and nondescript as it crossed the Atlantic Ocean and entered the eastern Pacific Ocean on June 19. An area of convection developed and organized along the wave's axis, and the National Hurricane Center began to employ Dvorak classifications on June 20. Convective banding features increased as the broad circulation became better defined, and on June 22, the disturbance developed into Tropical Depression Three-E about south of the Gulf of Tehuantepec. Well-defined steering currents resulted in a general west-northwestward movement. Deep convection concentrated near the center, and about 12 hours after becoming a tropical depression, the system strengthened into Tropical Storm Blas about south of Puerto Angel, Oaxaca.
Tropical Storm Blas continued to organize as it moved parallel to the Mexican coast. Banding features increased, and on June 23 the storm attained hurricane status about southwest of Acapulco. The next day, an eye developed and became apparent on satellite imagery, while upper-level outflow became better defined. Blas quickly strengthened and reached its peak intensity on June 25, with maximum sustained winds of , while about south-southeast of the southern tip of Baja California. Temperatures warmed in the convection around the eye, though the eye remained visible for several days as Blas turned west under the influence of a ridge to its north. On June 28, it degenerated into a tropical storm after entering an area of cooler water. Blas weakened to a tropical depression on June 30, and a day later was considered to have dissipated due to a lack of convection near the center. A remnant low-level cloud swirl persisted for several days, passing well to the south of Hawaii on July 5 before dissipating. The Associated Press attributed 4 deaths from a mudslide in Michoacán to Blas. However, as the primary convection remained offshore, the National Hurricane Center did not consider the deaths related to the hurricane. The threat of Blas prompted officials in Acapulco to close the port to all navigation.
Tropical Storm Celia
On July 1, another tropical wave emerged off the coast of Africa. It moved westward due to strong wind shear without further organization, and crossed Central America into the eastern Pacific Ocean on July 11. An area of organizing convection developed along the wave axis, and Dvorak classifications began on July 13, while the tropical wave was south of the Gulf of Tehuantepec. The cloud pattern soon became disorganized, and the area of disturbed weather continued west-northwestward. On July 16, convection increased and organized into banding features; early on July 17, the system developed into Tropical Depression Four-E about south of Manzanillo, Mexico. Soon after becoming a tropical depression, the storm rapidly organized and intensified into Tropical Storm Celia six hours after becoming a tropical depression. The tropical storm initially moved northwestward, and briefly threatened southern Baja California. As a result, the government of Mexico issued a tropical storm warning on July 18 for La Paz southward. Shortly thereafter, a mid- to upper-level anticyclone turned Celia to the west-northwest and forced it to pass about south-southwest of Cabo San Lucas. On July 19, Celia attained maximum sustained winds of before moving over cooler waters and diminishing in convection. The storm degenerated into a tropical depression on July 20, and Celia dissipated early on July 21, well away from the Mexican coastline.
The precursor tropical disturbance produced locally heavy rainfall along the south coast of Mexico. Authorities in Mexico closed the port at Acapulco to small fishing and recreational boats, and advised larger craft to use caution.
Hurricane Darby
A tropical wave moved off the coast of Africa on July 4. It tracked westward across the Atlantic Ocean with little increase in convection, and crossed Central America into the Pacific Ocean on July 16. Three days later, convection began to increase along the wave axis while the wave was well to the south of Acapulco, Mexico. On July 21, Dvorak classifications began as the cloud pattern displayed curvature on satellite images. Convective banding features gradually developed, and it is estimated that the system organized into Tropical Depression Five-E early on July 23 about south of the southern tip of the Baja California peninsula. Under the influence of a mid- to upper-level ridge to its north, the depression tracked west-northwestward. Convection became more concentrated as outflow organized further, and 18 hours after the depression first developed, it intensified into Tropical Storm Darby.