The 2012 Pacific hurricane season was a moderately active Pacific hurricane season that saw an unusually high number of tropical cyclones pass west of the Baja California Peninsula. The season officially began on May 15 in the eastern Pacific Ocean (east of 140°W), and on June 1 in the central Pacific (from 140°W to the International Date Line, north of the equator; they both ended on November 30. These dates conventionally delimit the period of each year when most tropical cyclones form in these regions of the Pacific Ocean. However, the formation of tropical cyclones is possible at any time of the year. This season's first system, Tropical Storm Aletta, formed on May 14, and the last, Tropical Storm Rosa, dissipated on November 3.
Hurricane Bud intensified into the first major hurricane of the season, one of three to do so in the month of May. In mid-June, Hurricane Carlotta came ashore near Puerto Escondido, Mexico. Seven people were killed by Carlotta and damage amounted to US$12.4 million. Hurricane Paul brought significant damage to Baja California Sur. Tropical Storms Hector, John, Kristy, and Norman, as well as Hurricane Fabio all threatened land; however, damage from these storms were relatively minor.
Seasonal forecasts
In advance of each Pacific hurricane season, forecasts of hurricane activity are issued by the United States National Oceanic and Atmospheric Administration (NOAA)'s Climate Prediction Center and Mexico's Servicio Meteorológico Nacional (SMN). These include weekly and monthly changes in significant factors that help determine the number of tropical storms, hurricanes, and major hurricanes within a particular year. According to NOAA, the average eastern Pacific hurricane season between 1971 and 2006 contained roughly 15 tropical storms, 8 hurricanes, 3 major hurricanes, with a near-normal accumulated cyclone energy (ACE) index of 113. Broadly speaking, ACE is a measure of the power of a tropical or subtropical storm multiplied by the length of time it existed. It is only calculated for full advisories on specific tropical and subtropical systems reaching or exceeding wind speeds of 39 mph (63 km/h). NOAA typically categorizes a season as above-average, average, or below-average based on the cumulative ACE index, but the number of tropical storms, hurricanes, and major hurricanes within a hurricane season is sometimes also considered.
On May 24, the Climate Prediction Center released its pre-season outlook. The scientists stated a 30% chance of a below-normal season, a 50% chance of a near-normal season and a 20% chance of an above-normal season. The climatologists expected 12–18 named storms, with 5–9 becoming hurricanes, and 2–5 becoming major hurricanes. The below-normal activity forecast was because of increased wind shear and a high expectation of El Niño–Southern Oscillation (ENSO)-neutral conditions throughout the peak in the later months of summer, together with lingering La Niña conditions at the beginning of the season, even though there had already been two named systems – one tropical storm and one major hurricane – in the month of May.
Seasonal summary
The season officially began on May 15 in the eastern Pacific and June 1 in the central Pacific; both ended on November 30. The season began with the formation of Tropical Storm Aletta on May 14, one day before the official start of the hurricane season in the eastern Pacific. On May 20, the second named storm of the season, Hurricane Bud, formed. It intensified to a Category 3 hurricane on the Saffir–Simpson hurricane wind scale, the first major hurricane of the season and also the third major occurrence of such. In June, Hurricane Carlotta intensified into a Category 2 hurricane. Carlotta made landfall as a Category 2 hurricane in southwestern Mexico, causing general damage. Carlotta killed seven people in Mexico and caused an estimated $12.4 million in damage (2012 USD). In July, three tropical cyclones formed, two of which were major hurricanes. Hurricane Emilia intensified as a Category 4 hurricane, becoming the most intense hurricane of the 2012 season. With the formation of Hurricane Fabio on July 12, the season was a month ahead of normal.
In August, three tropical cyclones formed, with two of them becoming hurricanes, Gilma and Ileana. September was the busiest month of the season, with the formation of five named storms, two of which were hurricanes. Hurricane Miriam, formed on September 22, became the fourth major hurricane of the season. In October, three named storms formed, one of which became the fifth and last major hurricane of the season. Hurricane Paul formed on October 13 and caused damage in the Baja California Peninsula. No deaths were reported from the hurricane, and the estimated total damage was $15.5 million (2012 USD). The season concluded with the formation of Tropical Storm Rosa on October 30. It dissipated on November 3 without affecting land. Storm activity in the Central Pacific Hurricane Center's area of responsibility was below average, with no tropical cyclones forming in the region. However, one tropical cyclone, Hurricane Daniel, entered the Central Pacific, as a tropical storm. The accumulated cyclone energy (ACE) index for the 2012 Pacific hurricane season as calculated by Colorado State University using data from the National Hurricane Center was 98.5 units.
Systems
Tropical Storm Aletta
The passage of an eastward-moving kelvin wave generated a broad area of low pressure within the Intertropical Convergence Zone well south of Mexico on May 11. Convection organized about this low, leading to the season's first tropical depression around 12:00 UTC on May 14. A ridge extending from Mexico into the eastern Pacific forced the depression west, while low wind shear and warm ocean temperatures allowed it to become Tropical Storm Aletta by 00:00 UTC on May 15. After attaining peak winds of 50 mph (80 km/h) eighteen hours later, stronger upper-level winds and dry air caused a steady decay of the system. Aletta weakened to a tropical depression as it curved northeast early on May 17, and despite producing intermittent bursts of convection for a few days, ultimately degenerated to a remnant low around 06:00 UTC on May 19. The low turned southeast and dissipated the next day.
Hurricane Bud
A tropical wave that left Africa on May 5 organized into a tropical depression over the East Pacific around 18:00 UTC on May 20. Easterly wind shear prevented much organization, and the depression did not intensify into Tropical Storm Bud until 06:00 UTC on May 22. As the system moved west-northwest, upper-level winds gradually diminished, allowing Bud to attain hurricane strength by 00:00 UTC on May 24. A period of rapid intensification brought the system to its peak as a Category 3 hurricane with winds of 115 mph (185 km/h) within 24 hours, when it resembled an annular hurricane with a distinct eye and little outer banding. A trough over the southwestern United States directed the storm northeast, while increasing southwesterly wind shear prompted weakening. Bud fell to tropical storm intensity by 00:00 UTC on May 26 and degenerated to a remnant low six hours later. The remnants moved very close to the coastline of southwestern Mexico before dissipating on May 26.
Hurricane Carlotta
An area of disturbed weather that may have originated as a tropical wave from Africa emerged into the East Pacific on June 11. Light wind shear and an eastward-moving kelvin wave aided in the development of a tropical depression by 00:00 UTC on June 14, and Tropical Storm Carlotta six hours later. As the storm moved northwest on the periphery of a mid-level ridge, it attained hurricane strength around 12:00 UTC on June 15 and rapidly intensified to its peak as a Category 2 with winds of 110 mph (175 km/h) by 21:00 UTC that day. Carlotta subsequently made landfall near Puerto Escondido, Mexico, at a slightly reduced strength, becoming the easternmost landfalling hurricane on record in the East Pacific. After the storm moved ashore, it rapidly weakened over the mountains terrain of southern Mexico, degenerating to a remnant low around 00:00 UTC on June 17 and dissipating over Guerrero twelve hours later.
Upon formation, hurricane watches were issued for the southern coastline of Mexico. This was later upgraded to a warning when Carlotta became a hurricane. The storm made landfall in southern Mexico, bringing with it heavy rains and gusty winds which caused flash floods and numerous landslides along the area, primarily the state of Oaxaca. Due to the severity of the situation in Oaxaca the governor requested for a state of emergency to be declared to his state. Throughout Mexico, seven people were killed by Carlotta and damage amounted to MX$1.4 billion (US$107.7 million).
Hurricane Daniel
A tropical wave emerged off Africa on June 20 and moved inconspicuously across the Atlantic, crossing Central America nine days later. The disturbance organized into a tropical depression around 06:00 UTC on July 4 and further strengthened into Tropical Storm Daniel after 24 hours. Moderate easterly wind shear affected the storm initially, but these winds relaxed and allowed Daniel to become a hurricane by 00:00 UTC on July 7 when an eye became apparent on satellite. Steady intensification brought the storm to its peak as a Category 3 with winds of 115 mph (185 km/h) around 06:00 UTC on July 8. A westward track into cooler waters and drier air caused Daniel to begin slowly; it fell to tropical storm strength by 06:00 UTC on July 10, weakened to a tropical depression around 18:00 UTC on July 11 shortly after crossing into the Central Pacific, and subsequently degenerated to a remnant low by 12:00 UTC on July 12. The low opened up into a trough early on July 14.
Hurricane Emilia
A quick-moving tropical wave left Africa on June 23 and emerged into the East Pacific late on July 4, where it interacted with a disturbance within the ITCZ. The two systems coalesced, leading to the formation of a tropical depression by 18:00 UTC on July 7, and to Tropical Storm Emilia six hours later. A mid-level ridge extending west from Mexico directed the cyclone west-northwest, while a favorable environment allowed Emilia to intensify. It attained hurricane strength around 06:00 UTC on July 9 with the formation of a banded eye, and further strengthened to a Category 4 with winds of 140 mph (225 km/h) a day later when its eye was embedded within very deep convection. The onset of an eyewall replacement cycle caused Emilia to weaken to a Category 2 hurricane early on July 11, but it regained Category 3 intensity later that day before entering cooler waters and a drier environment. Emilia weakened to a tropical storm around 12:00 UTC on July 13 and degenerated to a remnant low by 18:00 UTC on July 15. The post-tropical cyclone continued west and opened into a trough south of Hawaii early on July 18.
Hurricane Fabio
On June 27, a tropical wave left Africa; it tracked west, emerging into the East Pacific on July 7. Interaction with a series of eastward-moving kelvin waves led to the formation of a tropical depression around 00:00 UTC on July 12; six hours later, it became Tropical Storm Fabio. The storm moved west amid modest wind shear, becoming a hurricane by 18:00 UTC on July 13 and gradually strengthening to a Category 2 with winds of 110 mph (175 km/h) around 06:00 UTC on July 15. At its best, the hurricane was characterized by a distinct eye within deep convection, and it was possible Fabio briefly attained major hurricane strength. The system turned northwest and then north into cooler waters after peak, weakening to a tropical storm late on July 16, to a tropical depression early on July 18, and finally to a remnant low around 12:00 UTC that morning. The low curved east-southeast before dissipating on July 20.
Hurricane Gilma
A tropical wave departed Africa on July 27. Hampered by strong upper-level winds across the central Atlantic, it entered the East Pacific on August 2, where interaction with a kelvin wave led to an uptick in convection. Further organization ensued and a tropical depression formed around 06:00 UTC on August 7; the depression intensified into Tropical Storm Gilma twelve hours later. On a west-northwest heading, the newly formed system intensified within a favorable environment, attaining hurricane strength by 18:00 UTC on August 8 and reaching peak winds of 80 mph (130 km/h) several hours later. Increasing wind shear and decreasing ocean temperatures weakened Gilma beginning on August 9; it fell to tropical storm status around 18:00 UTC that day and gradually degenerated to a remnant area of low pressure by 12:00 UTC on August 11. The low turned southwest before dissipating well away from land on August 14.