The 2010 Pacific hurricane season was the least active Pacific hurricane season on record (reliable records began in 1971), tied with 1977 season. The season accumulated the second-fewest ACE units on record, as many of the tropical cyclones were weak and short-lived. Altogether, only three of the season's eight named storms strengthened into hurricanes. Of those, two became major hurricanes, with one, Celia, reaching Category 5 intensity on the Saffir-Simpson scale. Despite the inactivity, however, it was the costliest Pacific hurricane season on record at the time, mostly due to Tropical Storm Agatha. The season officially began on May 15 in the eastern North Pacific (east 140°W) and on June 1 in the central North Pacific (from 140°W to the International Date Line). It ended in both regions on November 30. These dates, adopted by convention, historically describe the period in each year when most tropical cyclogenesis occurs in these regions of the Pacific. However, the formation of tropical cyclones is possible at any time of the year, as evidenced by the formation of Tropical Storm Omeka on December 19.
The first system of the season, Agatha, developed on May 29 near the coast of Guatemala. In the second week of June, a sudden spree of tropical cyclones developed, and between June 16 and 22, four cyclones formed, including the two major hurricanes of the season, Celia and Darby, the first of which reached Category 5 intensity. This near-record activity was a reversal from the previous season, when no storm formed until June 18. Following this activity, July saw zero named storms. In August and September only 2 tropical storms and one hurricane formed. Tropical Depression Eleven-E caused a great deal of flooding in southern Mexico, causing millions of dollars in damage, as well as causing over 50 deaths and $500 million in damage in areas of Oaxaca and Guatemala. Tropical Storm Omeka was a rare off-season storm.
Seasonal forecasts
On May 19, 2010, the National Oceanic and Atmospheric Administration (NOAA) released their forecast for the 2010 Central Pacific hurricane season, which would start on June 1. They expected two or three cyclones to form in or enter the region throughout the season, below the average of four or five storms. The below-average activity forecast was based on two factors: the first was the continuance of a period of decreased activity in the central Pacific; and second, the effects of a Neutral El Niño–Southern Oscillation (ENSO) or La Niña, both of which reduce cyclone activity in the region. However, in light of the near-miss of Hurricane Felicia the previous year, forecasters at the Central Pacific Hurricane Center gave the public a basic message for the 2010 season, "Prepare! Watch! Act!".
On May 27, 12 days after the official start of the 2010 eastern Pacific hurricane season, NOAA released their forecast for the basin. Similar to the forecast for the central Pacific, below-average activity was expected, with nine to fifteen named storms forming, four to eight of which would become hurricanes and a further one to three would become major hurricanes. This lessened activity was based on the same two factors as the central Pacific, decreased activity since 1995 and the ENSO event. Overall, NOAA stated there was a 75% chance of below-average activity, 20% of near-normal and only a 5% chance of above-average due to a strong La Niña.
Seasonal summary
Background
The Accumulated Cyclone Energy (ACE) index for the 2010 Pacific hurricane season (Eastern Pacific and Central Pacific combined) as calculated by Colorado State University using data from the National Hurricane Center was 51.2 units. This ranked as the second-quietest since 1966. The vast majority of the ACE stemmed from Hurricanes Celia and Darby, which collectively accounted for roughly 70 percent of the seasonal total.
Continuing a trend of below-average activity that began in 1995, the 2010 season was quiet as expected. The Eastern Pacific proper saw record-low numbers of named storms and hurricanes, with only seven and three respectively forming. Inclusive of the Central Pacific, the basin tied its record low activity of eight named storms set in 1977.
Inactivity was largely attributed to a moderately strong La Niña event which resulted in below-average sea surface temperatures across the basin. Another major factor limiting storm formation was the eastward displacement of 200 mb divergence. The displacement of this feature brought conditions that favor tropical development closer to the rugged terrain of Mexico and Central America, a factor known to disrupt low-level circulations. Accordingly, six of the seven named storms in the Eastern Pacific proper formed east of 106°W, four of which originated over the Gulf of Tehuantepec where the greatest depth of warm waters were restricted to. A final limiting factor was above-average wind shear across much of the basin east of 130°W and north of 10°N.
The record inactivity experienced in the Northeastern Pacific also took place in the Northwestern Pacific. Since reliable records began in the 1970s, there has been no precedent for both basins experiencing exceptionally low tropical cyclone formation. Moreover, this general lack of storm formation was reflected in all cyclone basins except the Atlantic. On average, the Northeastern Pacific accounts for 16 percent of the world's storms; however, during 2010, it accounted for roughly 10 percent (7 out of 67 cyclones).
Early to peak intensity
The season began with record-high activity, featuring two major hurricanes in June. ACE values exceeded 300 percent of the long-term mean, though most was due to Category 5 Hurricane Celia. Hurricane Celia was also the second-earliest forming storm of that intensity during the course of a season, surpassed only by Hurricane Ava in 1973. The month featured an ACE value of 37.22, eclipsing the previous record set in 1984. Furthermore, Darby was the earliest second major hurricane of a season, eclipsing Hurricane Daniel (1978); however, this has since been surpassed by Cristina in 2014, Blanca in 2015, and Bud in 2018. This activity abruptly halted and languished throughout the month of July. No named storms developed during the month, marking the first such occurrence since 1966. However, due to the activity in June, ACE value for the season by the start of August remained slightly above normal, roughly 107 percent the yearly mean.
Late activity
Through the remainder of the season, the basin observed record low activity with only three additional named storms developing. Since Omeka was the first storm in the Central Pacific during the year, it marked the latest start to a season since reliable records began, excluding seasons with no storms.
Systems
Tropical Storm Agatha
Early May 29, the season's first tropical depression consolidated near the Gulf of Tehuantepec. Large-scale southwesterly flow prompted the system to move slowly northeast. Scatterometer data indicated the depression soon strengthened into a tropical storm, at which time it was assigned the name Agatha. Attaining peak winds of 45 mph (70 km/h), Agatha soon made landfall late on May 29 near Champerico, Guatemala, just south of the border with Mexico. Once onshore, the mountainous terrain of Guatemala caused the storm to quickly dissipate early on May 30.
Although a weak tropical cyclone, Agatha brought torrential rainfall to much of Central America. Daily accumulations peaked at 16.78 in (426 mm) in Montufar, Guatemala and 19.0 in (483 mm) in Ilopango, El Salvador. According to Guatemala's president, Álvaro Colom, some areas received more than 3.3 ft (1 m) of rain. The ensuing flash floods and landslides proved catastrophic, especially in Guatemala where at least 174 people died. In El Salvador, 11 people were killed and damage from the storm reached $112.1 million. Honduras also suffered significant losses from the storm with 18 fatalities and at least $18.5 million in damage. One person was also killed in Nicaragua.
The storm also associated with a very large sinkhole.
Tropical Depression Two-E
A tropical wave emerged off the west coast of Africa on June 2 and entered the Atlantic Ocean. Tracking westward, the system eventually reached the eastern Pacific on June 13. As it approached the Gulf of Tehuantepec, convection increased, despite strong wind shear. Early on June 16, sufficient development had taken place for the NHC to classify the wave as a tropical depression, at which time the depression was situated roughly 110 mi (175 km) south of Salina Cruz, Mexico. A scatterometer pass over the storm revealed it to have attained peak winds of 35 mph (55 km/h) later that day. Thereafter, wind shear took its toll on the system and its low-level circulation ultimately dissipated early on June 17 while still off the coast of Mexico.
Due to its proximity to land, tropical storm watches and warnings were issued in advance of the storm when the system was first classified. This was discontinued when the system dissipated. Rainfall associated with the depression extended as far north as Oaxaca. In San Juan Bautista Tuxtepec, 82 homes were damaged by flood waters and 40 others were affected in the town of Zimatlán de Alvarez. Some homes lost their roofs and a few trees were downed as a result of high winds.
Tropical Storm Blas
On May 30, a new tropical wave moved off the west coast of Africa and entered the Atlantic Ocean. Little convective development took place as it traversed the region; however, as it crossed Central America between June 9 and 10, it began to show signs of strengthening. By June 13, an area of low pressure developed within the wave and slowly developed a surface circulation over the following 48 hours as it remained nearly stationary over open waters. Early on June 17, deep convection was able to maintain itself over the system, prompting the NHC to classify the low as Tropical Depression Three-E; at this time, the depression was situated 305 mi (490 km) south-southwest of Manzanillo, Mexico. Within hours of becoming a tropical depression, a ship in the region reported sustained winds of 45 mph (70 km/h), indicating that the system had developed into a tropical storm. The newly upgraded storm, now named Blas by the NHC, began to track slowly to the northwest, and later nearly due west, in response to a strengthening ridge over Mexico.
Strong wind shear prevented Blas from strengthening further over the following day; however, by June 19, the system entered a region of weaker shear. This allowed convection to develop over the center of circulation and that afternoon, the storm attained its peak intensity with winds of 65 mph (105 km/h) and a pressure of 992 mbar (hPa; 29.29 inHg). Shortly thereafter, cooler sea surface temperatures took their toll on Blas, causing the storm to gradually weaken. By June 21, the system weakened to a tropical depression as convection diminished. Hours later, it degenerated into a non-convective remnant low while situated about 715 mi (1,151 km) west-southwest of the southern tip of Baja California Sur. The remnants of Blas persisted through June 23 as they continued westward, before it dissipated to a weak upper-level low.
Hurricane Celia
On June 5, 2010, a tropical wave exited western Africa and traversed westward across the Atlantic Ocean. The system eventually crossed Central America and entered the Pacific Ocean on June 17. Thereafter, the thunderstorms increased along the wave axis as the system moved toward the west-northwest, steered by a ridge to the north. A low-pressure area formed on June 18, which continued to organize. Around 18:00 UTC that day, Tropical Depression Four-E developed about 370 mi (590 km) southeast of Acapulco, Mexico. The thunderstorms diminished before redeveloping and becoming better organized. Around 12:00 UTC on June 19, the National Hurricane Center (NHC) to upgrade the depression to Tropical Storm Celia. Around that time, the storm had an eye-like feature, consisting of a ring of convection around the circulation. which continued to organize within the central dense overcast. Celia moved generally to the west to west-southwest and continued to intensify despite northeasterly wind shear. At 18:00 UTC on June 20, Celia attained hurricane status, with maximum sustained winds of 75 mph (120 km/h).
Wind shear displaced the circulation and restricted outflow. On June 22, Celia strengthened to a Category 2 on the Saffir-Simpson scale. It weakened slightly the next day, and the eye became no longer visible on satellite imagery. The following morning, the eye reformed and the storm became more vertically aligned, allowing Celia to re-attain Category 2 status on June 23. The hurricane briefly weakened again as the eye dissipated. On June 24, the wind shear decreased, allowing Celia to restrengthen again as the eye reformed and became symmetrical. At 00:00 UTC on June 25, Celia attained maximum sustained winds of 160 mph (255 km/h) and a barometric pressure estimated at 921 mbar (hPa; 27.20 inHg). This made it a Category 5 on the Saffir-Simpson scale, the first Pacific hurricane of that intensity in June since Hurricane Ava in 1973. At its peak, Celia had a well-defined eye estimated to be 17 to 23 mi (27 to 37 km) in diameter. After maintaining peak winds for about 12 hours, Celia began weakening due to cooler waters and higher wind shear. On June 27, it fell to tropical storm status as the track slowed and shifted to the west-southwest, after the ridge weakened that was previously guiding Celia. The storm lost all convection on June 28, and degenerated into a remnant low. The remnants of Celia executed a small loop before drifting to the north and dissipating on June 30, located about 990 mi (1,590 km) southwest of the southern tip of Baja California Sur.