The 2007 Pacific hurricane season was a well below-average Pacific hurricane season, featuring only one major hurricane. 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 the region. The first tropical cyclone of the season, Alvin, developed on May 27, while the final system of the year, Kiko, dissipated on October 23. Due to unusually strong wind shear, activity fell short of the long-term average, with a total of 11 named storms, 4 hurricanes, and 1 major hurricane. At the time, 2007 featured the second-lowest value of the Accumulated cyclone energy (ACE) index since reliable records began in 1971. Two tropical cyclones – Cosme and Flossie – crossed into the central Pacific basin during the year, activity below the average of 4 to 5 systems.
Impact during the season was relatively minimal. In early June, Tropical Storm Barbara moved ashore just northwest of the Mexico–Guatemala border, causing $55 million (2007 USD) in damage and 4 deaths. In late July, Cosme passed south of the island of Hawaii as a weakening tropical depression; light rain and increased surf resulted. A few days later, Dalila passed offshore the coastline of southwestern Mexico, killing 11 and causing minimal damage. Hurricane Flossie followed a similar track to Cosme in mid-August, producing gusty winds and light precipitation in Hawaii. Hurricane Henriette in early September produced torrential rainfall in southwestern Mexico, killing 6 and causing $25 million in damage. Baja California received moderate rains from Hurricane Ivo in mid-September, though no damage nor fatalities were reported. In mid-October, Tropical Storm Kiko passed just offshore the coastline of southwestern Mexico. Though no deaths were reported on the Mexico mainland, the storm capsized a ship with 30 people on board, 15 of whom were recovered dead, and 9 of whom were reported missing. Overall, the season ended with $80 million in damage and 49 deaths.
Seasonal forecasts
On May 21, 2007, the National Oceanic and Atmospheric Administration's Central Pacific Hurricane Center released its outlook for the 2007 Central Pacific hurricane season, predicting a total of 2–3 tropical cyclones to form or cross into the basin; in a typical season, 4–5 systems cross or form in the Central Pacific. A day later, the National Oceanic and Atmospheric Administration's Climate Prediction Center released its seasonal prediction for the 2007 East Pacific hurricane season, predicting a total of 11–16 named storms, 6–9 hurricanes, and 2–4 major hurricanes. Below-average activity was expected as a result of either ENSO-Neutral or La Niña conditions, as well as the continuation of the reduction in activity beginning in 1995.
Seasonal summary
The Accumulated Cyclone Energy (ACE) index for the 2007 Pacific hurricane season (Eastern Pacific and Central Pacific combined) as calculated by Colorado State University using data from the National Hurricane Center was 51.6 units, which was a well below the 1981–2010 average of 113.3 units, and at the time the second-lowest value observed since reliable records began in 1971. 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).
Tropical cyclone activity totaled to eleven named storms, four hurricanes, and only major hurricane within the season; all three of these values fall below the 1971–2006 long-term average of 15 named storms, 9 hurricanes, and 4 major hurricanes. The main contributing factor to below-average activity was much above-average wind shear across the Pacific basin. In May 2007, two tropical storms – Alvin and Barbara – developed, marking at the time the third such instance of more than one tropical storm developing within the month since official records began in 1949. In June 2007, only one tropical depression developed in the East Pacific basin, making 2007 one of only four years in which a tropical storm did not form in the month. By the following month, in terms of ACE, 2007 was considered the third quietest year-to-date since the satellite era began in 1966; in September, the season fell to the second quietest year-to-date. Below-average activity continued for the remainder of the year.
Systems
Tropical Storm Alvin
The genesis of Alvin can be attributed to a tropical wave that crossed Dakar, Africa on May 9. The wave remained poorly organized as it moved across the Atlantic Ocean and Caribbean Sea through mid-May. On May 20, the disturbance crossed Central America and emerged into the eastern Pacific Ocean, where convection—shower and thunderstorm activity—gradually began to increase over the well-defined center; this led to the formation of a tropical depression by 0000 UTC on May 27, approximately 345 mi (555 km) south of the southern tip of Baja California. Following designation, the depression was slow to organize as a result of moderate easterly shear; by 0000 UTC on May 29, however, the system had gained enough organization to be considered a tropical storm. After attaining its peak intensity with winds of 40 mph (64 km/h) and a minimum barometric pressure of 1003 mbar (1003 hPa; 29.6 inHg), increasingly stable air and higher wind shear caused Alvin to begin a weakening trend. At 0600 UTC on May 30, it weakened to a tropical depression, and by 0000 UTC on June 1, Alvin degenerated into a non-convective remnant low. The remnant low continued generally westward until dissipation six days later.
Tropical Storm Barbara
A tropical wave emerged off the western coast of Africa on May 14. After emerging into the eastern Pacific on May 25, the system acquired enough organization to be considered a tropical depression at 1800 UTC on May 29, about 115 mi (185 km) south-southeast of Puerto Escondido, Oaxaca. Within an environment of weak steering currents, the storm became better organized as evidenced by an improving satellite appearance, with the formation of a curved band in the southeast quadrant. At 1200 UTC on May 30, the depression was upgraded to a tropical storm; by 0000 UTC on June 1, however, increased northerly wind shear caused Barbara to weaken back to a tropical depression. After re-intensifying into a tropical storm for a second time six hours later, Barbara attained its peak intensity with winds of 50 mph (80 km/h) and a minimum barometric pressure of 1000 mbar (1000 hPa; 30 inHg) at 1800 UTC. Drifting northeast, the storm maintained this intensity until landfall just northwest of the Mexico-Guatemala border at 1300 UTC on June 2. Rapid weakening ensued thereafter, with the system weakening to a tropical depression at 1800 UTC. The low-level circulation dissipated six hours later, marking the dissipation of Barbara.
Heavy rainfall exceeding 4 in (100 mm) caused many rivers to swell. An unspecified island was separated from the Mexico mainland after the bridge connecting the two was washed away, stranding dozens of families. In El Salvador, significant flooding killed four people. Gusts peaked at 58 mph (93 km/h) at an automated weather station in Puerto Madero, Chiapas. Across the affected regions, these winds caused damage limited to house roofs and trees. Barbara caused severe crop damage totaling to 200 million pesos (2007 MXN; $55 million). About a hundred residents were forced to evacuate after the storm destroyed a dozen palm huts in Guatemala.
Tropical Depression Three-E
On May 24, a tropical wave emerged off the western coast of Africa. The wave entered the eastern Pacific around June 6 and shower and thunderstorm activity began to increase shortly thereafter. A broad area of low pressure formed a few hundred miles south of Acapulco, Mexico two days later. Following satellite evidence of a well-defined circulation and organized convective activity, the National Hurricane Center upgraded the disturbance to a tropical depression at 1200 UTC on June 11. After attaining winds of 35 mph (56 km/h) and a minimum barometric pressure of 1004 mbar (1004 hPa; 29.6 inHg), the depression began to traverse cooler waters and much more stable air. This caused all associated convection to fade away, and the depression degenerated to a non-convective remnant low at 0000 UTC on June 13. The remnant low continued northwest until dissipation by 0600 UTC on June 15.
Tropical Depression Four-E
A tropical wave emerged off the western coast of Africa on June 23. It reached the eastern Pacific on July 3, where associated convection began to increase three days later. Continued slow development occurred thereafter, and following satellite trends, the disturbance was upgraded to Tropical Depression Four-E at 1800 UTC on July 9. Tracking westward, the depression began to move across waters too cool to support a tropical cyclone and into an environment of moderate shear. The low-level circulation became ill-defined and exposed, leading to degeneration to a remnant low at 0600 UTC on July 11 about 910 mi (1,460 km) west-southwest of Cabo San Lucas, Mexico. The low continued northwest until dissipation at 0000 UTC the following day.
Tropical Depression Five-E
On June 21, a tropical wave emerged off the western coast of Africa. It entered the eastern Pacific on July 10, and shower and thunderstorm activity began to increase a day later as a result. Tracking westward, the wave gradually became better organized; by 1200 UTC on July 14, the disturbance acquired enough organization to be upgraded to a tropical depression. Within an environment of moderate wind shear, the low-level center quickly became poorly defined as convection dissipated. Turning west-northwest on July 15, the depression entered cooler waters and an increasingly stable airmass, causing the system to degenerate into a remnant low by 0000 UTC the following day. The remnant low dissipated a few hours later.
Hurricane Cosme
A tropical wave emerged off the western coast of Africa on June 27 and tracked westward to reach the eastern Pacific on July 8. Initially embedded within the ITCZ, development was slow until the system's convection increased on July 13. A day later, the NHC classified it as Tropical Depression Six-E about midway between Mexico and Hawaii. Although wind shear was light, ocean temperatures were marginal for intensification, and the depression intensified into Tropical Storm Cosme on July 15, while moving generally northwestward. Following the development of a curved convection band and appearance of an eye on satellite, Cosme was upgraded to a Category 1 hurricane at 1800 UTC the next day, about 1,600 mi (2,600 km) east of Hilo, Hawaii; it is at this time that the hurricane attained its peak with winds of 75 mph (121 km/h) and a minimum barometric pressure of 987 mbar (987 hPa; 29.1 inHg). Cosme tracked westward over cooler waters, causing the system to weaken quickly back to tropical storm strength. At 1800 UTC on July 18, Cosme weakened to a tropical depression after crossing into the central Pacific. Gradually weakening, Tropical Depression Cosme passed south of the Hawaiian Islands on July 20 with a minimum central pressure of 1010 mbar. By late on July 22, Cosme degenerated into a remnant low near Johnston Island. The circulation dissipated three days later.
Cosme was initially forecast to pass over Hawaii at tropical storm strength. In anticipation of the storm, the National Weather Service issued a flash flood watch for the island of Hawaii on July 20, and a small craft advisory and high surf advisory for Maui and Hawaii. The Hawaii County Civil Defense opened evacuation centers, while county crews cleaned out drains and culverts to prevent flooding. Because the depression stayed far from land, the effects were mostly minor. Rain bands produced 6.94 in (176 mm) of rainfall in Hakalau, causing small stream and drainage ditch flooding, as well as ponding on roadways in portions of Hilo, Puna, and Kau. The rainfall helped to relieve a persistent drought which had existed for several months. Wind gusts reached 40 mph (64 km/h) in southern portions of Hawaii. A strong trade wind swell north of Cosme generated waves up to 9 ft (2.7 m) high.
Tropical Storm Dalila
A tropical wave emerged into the eastern Pacific on July 17. Tracking west-northwest, the system acquired enough organization to be upgraded to a tropical depression at 0000 UTC on July 22, while positioned 460 mi (740 km) south of Manzanillo, Mexico. Following formation, moderate northeasterly shear inhibited significant development, causing the system to remain a tropical depression for 48 hours. A mid-level ridge over Mexico caused the system to turn northwest as shear began to decrease; at 0000 UTC on July 24, the depression was upgraded to Tropical Storm Dalila. After attaining its peak intensity with winds of 60 mph (97 km/h) and a minimum barometric pressure of 995 mbar (995 hPa; 29.4 inHg) a day later, the storm tracked over progressively cool waters, causing it to weaken. At 0600 UTC on July 27, Dalila weakened to a tropical storm, and by 1800 UTC, the system no longer retained enough organization to be considered a tropical cyclone. The remnant low tracked west, southwest, and eventually south prior to dissipation at 1200 UTC on July 30.
Though the center of the storm remained offshore, outer rainbands led to heavy rainfall that triggered substantial flooding. In Michoacán, Dalila flooded ten municipalities with at least 15 in (380 mm) of precipitation, destroying dozens of wooden structures. Heavy rains in Jalisco killed eleven, many of whom occurred in automobile crashes. Flood waters covered numerous roads, causing many accidents, while approximately 50 homes were damaged. Rough seas and heavy rain affected Baja California Sur, though no damage or fatalities were reported.