The 2009 Pacific hurricane season was the most active Pacific hurricane season since 1997. 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 Pacific basin. The first tropical cyclone to form was One-E on June 18, and the last, Hurricane Neki, dissipated on October 27.
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 .
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 or tropical storm strength.