2010 Pacific hurricane season

A record-quiet year under La Niña

Forecasters expected a below-normal year. In late May, NOAA predicted 9 to 15 named storms in the eastern Pacific, pointing to the basin's long run of reduced activity since 1995 and to the developing La Niña. The season ended up near or below the bottom of that range, and its accumulated cyclone energy (ACE) came to 51.5 units in the site's archive, a small fraction of a typical year.

A moderately strong La Niña cooled sea surface temperatures across much of the basin. Upper-level divergence, which supports thunderstorm growth, was displaced eastward toward the mountains of Mexico and Central America, where rugged terrain tends to disrupt young circulations. Most of the named storms therefore formed east of 106°W, several of them over the Gulf of Tehuantepec, and stronger than usual wind shear covered much of the basin farther west and north.

The quiet was not limited to the eastern Pacific. The northwestern Pacific also had exceptionally low storm formation in 2010, and storm formation was low in every basin worldwide except the Atlantic.

A June burst, then a long lull

Tropical Storm Agatha opened the season on 29 May, forming south of the Gulf of Tehuantepec and moving ashore in Guatemala within a day. Then, between 16 and 23 June, four cyclones formed in quick succession: a short-lived depression off southern Mexico, Tropical Storm Blas, Hurricane Celia and Hurricane Darby. June's ACE broke the previous record for the month, set in 1984, and was more than three times the long-term June average.

The activity stopped abruptly. July produced only a weak depression and no named storm, the first July without one since 1966. When Tropical Storm Estelle formed on 6 August, it was the first tropical storm in the basin for 44 days, during what is normally one of the busiest stretches of the year.

The late season stayed thin. Hurricane Frank formed south of the Gulf of Tehuantepec on 21 August, two short-lived depressions developed in early September, and Tropical Storm Georgette formed south of Baja California Sur on 20 September. Georgette's final tropical observation on 23 September is the last in the site's archive for the season, and no further storms formed east of 140°W before the season officially ended on 30 November.

Celia, Darby and Frank

Hurricane Celia was the strongest and longest-lived storm of the season. It spent several days held between 65 and 85 kt by northeasterly wind shear south of Mexico. When the shear eased on 24 June, it strengthened from 90 to 140 kt in about 18 hours, peaking near 00:00 UTC on 25 June with a central pressure of 921 hPa. That made Celia a Category 5 hurricane, tied with Hurricane Ava of 1973 as the strongest June hurricane on record in the eastern Pacific. It then weakened quickly over cooler water and never affected land.

Hurricane Darby formed on 23 June, while Celia was still intensifying farther west. It was a very small cyclone, with an eye less than 10 nautical miles across, and it went through two bursts of rapid intensification to reach 105 kt on 25 June, a Category 3 hurricane. Darby was then pulled into the enormous circulation of Hurricane Alex in the Gulf of Mexico. Alex's outflow sheared the tiny storm apart, and Darby dissipated off southern Mexico on 29 June, weakening faster than it had strengthened.

Hurricane Frank was the only hurricane after June. It moved west on a track close to and parallel with the southwestern coast of Mexico, recovered from a spell of shear, and reached its peak of 80 kt on 26 August about 300 nautical miles south of the tip of Baja California. Its closeness to the coast required watches and warnings, and Socorro Island recorded a 44 kt gust as it passed.

Landfalls and impacts

Tropical Storm Agatha, one of the season's weaker storms, did by far its greatest harm. It came ashore near Champerico, Guatemala, late on 29 May with winds of 40 kt, one of very few tropical storm landfalls in Guatemala on record. Its rains fell during a wider stretch of heavy rain over Central America, and Montufar, Guatemala, reported 16.78 inches in 24 hours. In the NHC report, updated in January 2011, Guatemalan authorities counted 160 deaths with 47 people missing, and US aid reports gave 18 deaths in Honduras and 12 in El Salvador. The report estimated property damage at about $1.1 billion in US dollars of the time, including $982 million in Guatemala and $112 million in El Salvador, and noted a 20 m wide sinkhole that opened in Guatemala City.

Tropical Depression Eleven-E made landfall near Salina Cruz, Mexico, on 4 September, crossed the Isthmus of Tehuantepec and regenerated in the Bay of Campeche as Atlantic Tropical Storm Hermine. The NHC reported no casualties or damage directly from the depression. The broader monsoon flow around it, however, brought heavy rain to Central America, and mudslides from those rains killed 38 people in Guatemala.

Tropical Storm Georgette struck Baja California Sur on 21 September and then made a second landfall on mainland Mexico as a depression, bringing flooding to parts of Sonora. Its moisture later fed heavy rain in New Mexico, where flooding killed one person near the Rio Grande, a death Wikipedia classes as indirect, and damage in the United States came to about $72,000 in 2010 US dollars.

The season's strongest storms were far less damaging. The NHC reports for Celia, Darby, Blas and Frank list no damage or casualties, although Celia's early rainbands and surf reached parts of southern Mexico, and Darby's rains combined with those of Hurricane Alex over Chiapas.

How the season is counted

The site's count of 8 tropical storms comes from US-agency one-minute winds during the tropical stage, taken from the whole merged track of each system in the archive. On that basis Eleven-E counts as a tropical storm, because the same system later reached 60 kt as Hermine after crossing into the Atlantic. The NHC counts only its time in the eastern Pacific, when it stayed a depression, so the eastern Pacific proper had 7 named storms, a record low.

Wikipedia's total of 8 named storms, which ties 1977 for the fewest in the basin, uses a different set: the 7 eastern Pacific storms plus Tropical Storm Omeka, a rare December system in the central Pacific that is not among the storms on this page. Omeka began as a non-tropical low west of the International Date Line and became a tropical storm after crossing east of it on 20 December. It was the latest tropical storm to form in the North Pacific east of the dateline since satellite records began in the mid-1960s. Both counts give 3 hurricanes and 2 major hurricanes. Colorado State University's ACE of 51.2 units, computed from NHC data for the eastern and central Pacific combined, is close to the site's 51.5, which uses IBTrACS one-minute winds over each system's merged track.