The 2009 Pacific hurricane season was the most active Pacific hurricane season since 1994. The season officially started on May 15 in the East Pacific Ocean, and on June 1 in the Central Pacific; they both ended on November 30. These dates conventionally delimit the period of each year when most tropical cyclones form in the Eastern Pacific tropical cyclone basin; however, tropical cyclone formation is possible at any time of the year. The first system of the season, Tropical Depression One-E, developed on June 18, and the last, Hurricane Neki, dissipated on October 27, keeping activity well within the bounds of the season.
For the first time since 1999, the first system of the season did not form until mid-June. Three days after One-E formed, the first named storm of the season, Hurricane Andres developed. Activity picked-up during peak-season, and according to the NHC's tropical weather summary, August 2009, with seven named storms in their region, was one of the most active Augusts on record for the basin. This level of activity had rarely occurred, if at all, in the past 41 years, since 1968, when the most active August on record for the region with eight named storms occurred. When Hurricane Rick reached Category 5 strength on October 17, it became the first Category 5 Pacific hurricane since Ioke in 2006, and the third-strongest Pacific hurricane on record, behind 2015's Patricia and 1997's Linda. The first Central Pacific name to be used was Lana, when it crossed into the region from the Eastern Pacific. With the naming of Tropical Storm Maka on August 11, this season became the first in seven years to use multiple Central Pacific names.
Seasonal forecasts
On May 21, 2009, NOAA released their forecast for the 2009 Eastern Pacific and Central Pacific hurricane seasons. They predicted a below-normal level of activity in the Eastern Pacific, with 13 to 18 named storms, of which 6 to 10 were expected to become hurricanes, and 2 to 5 expected to become major hurricanes. The forecast was based on the dissipation of a La Niña in April 2009. Sea surface temperatures were near normal around the equator makes the season an ENSO-neutral. Additionally, an El Niño was forecast to develop during the latter part of the season. Depending on the intensity of the El Niño, forecasters were unsure of whether or not it would have an effect on the overall activity in the basin. However, due to the low-activity cycle that began in 1995, the El Niño only brought the activity to a slightly above normal season.
The Central Pacific basin was also expected to be slightly below average, with three to five tropical cyclones expected to form or cross into the area. However, it was slightly more active than expected, the number of three to five was exceeded, as seven tropical cyclones moved into or formed in the Central Pacific.
Seasonal summary
The accumulated cyclone energy (ACE) index for the 2009 Pacific hurricane season as calculated by Colorado State University using data from the National Hurricane Center was 126.4 units. 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).
The season was characterized as "near-normal", featuring 17 named storms 8 hurricanes and 5 major hurricanes. The central Pacific experienced above-average activity with three additional storms forming west of 140°W and three more crossing over from the eastern Pacific. The overall number of storms contrasted to a relative lull in activity experienced over the previous decade. During the course of the year, large-scale factors such as an El Niño and two Madden–Julian oscillations greatly contributed to the changed pattern. The season's activity, east of 140°W, was reflected with a near-average cumulative accumulated cyclone energy (ACE) rating of 100, roughly 94% of the 30-year median. ACE is, broadly speaking, a measure of the power of the hurricane multiplied by the length of time it existed, so storms that last a long time, as well as particularly strong hurricanes, have high ACEs. ACE is only calculated for full advisories on tropical systems at or exceeding 34 kn (39 mph; 63 km/h) or tropical storm strength.
The season started at a below-average pace, with only one named storm forming by the end of June. This marked the first time since 1999 that no tropical storms formed during the month of May; however, on average only one storm develops in the month every other year. The ten-year span of May named storms marked the longest occurrence of this event. The first hurricane of the year, Hurricane Andres, also became the first June hurricane since Hurricane Carlotta in 2000. Below-average activity continued into July with four named storms forming. By the end of the month, season to date ACE values were roughly 37% of the long-term mean, the sixth lowest since reliable records began in 1971.
An abrupt shift in activity took place during August as seven named storms formed, three of which became major hurricanes. This marked the most storms to form in a single month since 1985 and the most in August since 1968. Of these storms, Hurricane Jimena became the first cyclone of the season to make landfall, as well as the strongest storm to strike the west coast Baja California Sur, alongside Hurricane Norbert in 2008. Following the well-above average August, September experienced below-average activity with ACE reaching 70% of the long-term mean. The final month of activity featured the third-strongest storm on record in the eastern Pacific: Hurricane Rick. A Category 5 storm, Rick attained winds of 180 mph (290 km/h) off the coast of Mexico on October 18 before succumbing to increased wind shear and dry air. ACE for the month was 59% above average, mostly attributed to Rick.
Systems
Tropical Depression One-E
The first system of the season, One-E formed out of a tropical wave on June 18 roughly 405 miles (652 km) south-southwest of Mazatlán and initially tracked slowly northwards. Throughout the day, convection developed around the center of circulation and the system was anticipated to become a tropical storm. Late on June 18, the National Hurricane Center noted that the system was on the verge of becoming a tropical storm. However, the following day, strong wind shear caused the depression to rapidly degenerate into a trough of low pressure before dissipating off the coast of Sinaloa.
Although no longer a tropical cyclone, the remnants of the depression brought moderate rainfall to parts of Sinaloa, Nayarit and Jalisco. High winds accompanied the rainfall and left about 50,000 residences without power. Several trees were downed and some structures sustained damage from fresh water flooding. Landslides occurred along major highways and significant structural damage was reported around Mazatlán. However, there was no loss of life or reports of injuries.
Hurricane Andres
Hurricane Andres formed on June 21 out of an area of disturbed weather associated with a shower and thunder storm that crossed Central America a few days earlier. Andres gradually intensified as it tracked along the Mexican coastline. Deep convection developed around the center of circulation and by June 23, the storm attained hurricane-status, peaking with winds of 80 mph (130 km/h). Upon attaining this intensity, the storm featured a developing eyewall within a central dense overcast. Within 36 hours, the storm rapidly degenerated, having most of the convection being displaced by high wind shear, becoming a non-tropical trough during the afternoon of June 24.
Prior to becoming a tropical depression, Andres produced heavy rainfall Oaxaca and Honduras, resulting in two deaths. Rough seas off the coast of Guerrero resulted in one fatality. Inland, flooding caused by heavy rains killed two people and injured twenty. Several dozen structures were damaged and a few were destroyed. Following the storm, roughly 350 people were left homeless.
Tropical Storm Blanca
A tropical wave exited the western coast of Africa on June 19, which moved westward across the Atlantic without development. By June 29, the wave crossed Central America into the eastern Pacific. Thunderstorms increased over the next several days, which organized into curved rainbands around a developing low-pressure area on July 4. Following further organization, the system developed into a tropical depression on July 6, located roughly 435 miles (700 kilometres) south of Cabo San Lucas, Mexico. Soon after, it strengthened into Tropical Storm Blanca. Operationally, the NHC classified the system immediately as a tropical storm. At that time, Blanca developed an eye-feature, though it was not expected to develop into a hurricane. Steered by a ridge to the north, the storm moved west-northwestward throughout its existence. Early on July 7, Blanca attained peak winds of 50 mph (80 km/h) and a barometric pressure of 998 mbar (hPa; 29.47 inHg). The storm's convection developed into a central dense overcast over the center, which soon began deteriorating, with cloud tops warming and convection shrinking. By late on July 7, the center became devoid of shower and thunderstorm activity, with only intermittent convection. On July 8, Blanca weakened into a tropical depression, and the next day it degenerated into a remnant low. Although no longer a tropical cyclone, the remnants of Blanca maintained a well-defined low pressure center as it continued its northwesterly movement. Early on July 11, the system turned northward and gradually weakened. By the following day, Blanca had dissipated over open waters.
Due to the developing storm, Mexican officials posted high seas advisories for Michoacán, Jalisco, Nayarit, Baja California Sur and Colima, and advised ships to remain at port in July 6. These advisories were discontinued the following day as Blanca moved out to sea. Moisture from the system enhanced a frontal system over Coahuila. The system produced upwards of 22.2 mm (0.87 in) in the span of a few hours, triggering flooding throughout the state. Numerous streets were closed due to flooding and local fire departments were deployed to assist in draining the water. No injuries or structural damage resulted from the flooding. The remnants of the storm also brought unseasonable rainfall, although negligible, to parts of southern and central California on July 11. The moisture reached the region after being pulled northward by an upper-level low off the coast of Oregon.
Hurricane Carlos
A tropical wave departed the west coast of Africa on June 25, which moved across the Atlantic without development. The wave entered the eastern Pacific on July 4, later developing more convection on July 8 to the south of Mexico. Early on July 10, convective banding features developed along the periphery of the system and an area of low pressure developed within the wave. On July 10, the NHC designated the system as Tropical Depression Four-E about 900 mi (1,400 km) south of the southern tip of the Baja California Peninsula. Soon after, it strengthened into Tropical Storm Carlos while moving westward through an area of warm waters and light wind shear. On July 11, Carlos intensified further into a minimal hurricane. At that time, the small storm developed a small eye-like feature, which had disappeared the next day, causing Carlos to weaken back into a tropical storm. The eye feature redeveloped, signaling that Carlos reintensified into a hurricane on July 14, reaching peak winds of 105 mph (169 km/h) early the next day. Located at 10.1ºN, this made Carlos the southernmost Category 2 hurricane in the eastern Pacific proper. Late on July 15, the hurricane encountered strong wind shear, resulting in rapid weakening. About 24 hours after its peak intensity, Carlos deteriorated into a tropical depression, and dissipated early on July 17 well to the southeast of Hawaii.
Tropical Storm Dolores
On July 11, a broad area of low pressure developed within a tropical wave several hundred miles south of Acapulco, Mexico. Shower and thunderstorm activity associated with the system gradually increased over the next several days as it tracked west-northwestward. By July 15, the low became sufficiently organized and was declared a tropical depression roughly 695 miles (1,118 km) of Manzanillo, Colima. Turning towards the northwest in response to a ridge over Mexico, the depression intensified into Tropical Storm Dolores later that day. Despite southwesterly wind shear displacing the center of Dolores from the deepest convection, the system continued to strengthen, attaining peak winds of 60 mph (97 km/h) on July 16. Shortly thereafter, convection associated with the storm dissipated, possibly due to entrainment of dry air. Later that day the system degenerated into a remnant low and gradually weakened. The remnants of Dolores eventually dissipated on July 19, roughly 995 miles (1,601 km) west-southwest of Los Angeles.