Pacific hurricane

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A Pacific hurricane is a tropical cyclone that develops in the Pacific Ocean north of the equator, between 180° and the west coast of North America. For tropical cyclone warning purposes, this area is divided into two regions: the Eastern North Pacific basin (North America to 140°W), and the Central North Pacific Basin (140°W to 180°). Identical phenomena in the western north Pacific are called typhoons. This separation between the two basins has a practical convenience, however, as tropical cyclones rarely form in the central north Pacific due to high vertical wind shear, and few cross the dateline.

Climatology

The presence of a semi-permanent high-pressure area known as the North Pacific High in the eastern Pacific is a dominant factor against the formation of tropical cyclones in the winter, as the Pacific High results in wind shear that causes unfavorable, environmental conditions for tropical cyclone formation. Its effects in the central Pacific basin are usually related to keeping cyclones away from the Hawaiian Islands. Due to westward trade winds, hurricanes in the Pacific rarely head eastward, unless recurved by a trough. A second factor preventing tropical cyclones from forming during the winter is the occupation of a semi-permanent low-pressure area designated the Aleutian Low between January and April. Its presence over western Canada and the northwestern United States contributes to the area's occurrences of precipitation in that duration. In addition, its effects in the central Pacific near 160° W causes tropical waves that form in the area to drift northward into the Gulf of Alaska and dissipate. The retreat of this low allows the Pacific High to also retreat into the central Pacific, leaving a warm and moist environment in its wake. The Intertropical Convergence Zone comes northward into the East Pacific in mid-May permitting the formation of the earliest tropical waves, coinciding with the start of the eastern Pacific hurricane season on May 15.

The El Niño–Southern Oscillation also influences the frequency and intensity of hurricanes in the Northeast Pacific basin. During El Niño events, sea surface temperatures increase in the Northeast Pacific and vertical wind shear decreases. Because of this, an increase in tropical cyclone activity occurs; the opposite happens in the Atlantic basin during El Niño, where increased wind shear creates an unfavorable environment for tropical cyclone formation. Contrary to El Niño, La Niña events increase wind shear and decreases sea surface temperatures over the eastern Pacific, while reducing wind shear and increasing sea surface temperatures over the Atlantic.

In the eastern Pacific, east of 140º W, the hurricane season begins on May 15. In the central Pacific, the season begins on June 1. Across the basin, activity typically peaks in August or September, and the season ends on November 30. The Regional Specialized Meteorological Center for this basin is the United States' National Hurricane Center, while the Central Pacific Hurricane Center is the RSMC for the central Pacific. Previous forecasters are the Eastern Pacific Hurricane Center and the Joint Hurricane Warning Center. The RSMC monitors the eastern Pacific and issues reports, watches and warnings about tropical weather systems and cyclones as defined by the World Meteorological Organization.^{[citation needed]}

This area is, on average, the second-most active basin in the world. There are an average of 16 tropical storms annually, with 9 becoming hurricanes, and 4 becoming major hurricanes.

History

Documentation of Pacific hurricanes dates to the Spanish colonization of Mexico, when the military and missions wrote about "tempestades". In 1730, such accounts indicated an understanding of the storms. After observing the rotating nature of tropical cyclones, meteorologist William Charles Redfield expanded his study to include storms in the eastern North Pacific Ocean in the middle of the 19th century. Between June and October 1850, Redfield observed five tropical cyclones along "the southwestern coast of North America", along with one in each of the three subsequent years. In 1895, Cleveland Abbe reported the presence of many storms between 5° and 15°–N in the eastern Pacific, although many such storms dissipated before affecting the Mexican coast. Two years later, the German Hydrography Office Deutsche Seewarte documented 45 storms from 1832 to 1892 off the west coast of Mexico.

Despite the documentation of storms in the region, the official position of the United States Weather Bureau denied the existence of such storms. In 1910, the agency reported on global tropical cyclones, noting that "the occurrence of tropical storms is confined to the summer and autumn months of the respective hemispheres and to the western parts of the several oceans." In 1913, the Weather Bureau reinforced their position by excluding Pacific storms among five tropical cyclone basins; however, the agency acknowledged the existence of "certain cyclones that have been traced for a relatively short distance along a northwest course... west of Central America."

After California became a state and the discovery of gold there in 1848, shipping traffic began increasing steadily in the eastern Pacific. Such activity increased further after the Panama Canal opened in 1914, and the shipping lanes moved closer to the coast. By around 1920, Pacific hurricanes were officially recognized due to widespread ship observations, radio service, and a newly created weather network in western Mexico. Within 60 years, further studies of the region's tropical activity indicated that the eastern Pacific is in fact the second most active basin in the world.

During the 1920s, a few documents in the Monthly Weather Review reported additional storms within 2,000 mi (3,200 km) off the Mexican coastline.

List of seasons

The Eastern and Central Pacific hurricane database

The Eastern Pacific hurricane best track database was initially compiled on magnetic tape in 1976 for the seasons between 1949 and 1975, at the NHC to help with the development of two tropical cyclone forecast models, which required tracks of past cyclones as a base for its predictions. The database was based on records held by the United States Navy and were interpolated from 12 hourly intervals to 6 hourly intervals based on a scheme devised by Hiroshi Akima in 1970. Initially tracks for the Central Pacific region and tracks for tropical depressions that did not develop into tropical storms or hurricanes were not included within the database. After the database had been created Arthur Pike of the NHC made some internal adjustments, while in 1980 a review was made by Arnold Court under contract from the United States National Weather Service and resulted in additions and/or modifications to 81 tracks in the database. Between 1976 and 1987, the NHC archived best track data from the Eastern Pacific Hurricane Center (EPHC), and in 1982 started including information on Central Pacific tropical storms and hurricanes started to be included in the database based on data from the Joint Typhoon Warning Center and research done by Samuel Shaw of the Central Pacific Hurricane Center (CPHC) in 1981.

The format of the database was completely revised by the NHC during 1984, so that the format could resemble the Atlantic database before they took over the warning responsibility from the EPHC for the Eastern Pacific during 1988. During 2008 and 2013 several revisions were made to the database to extend tracks in land, based on reports in the Mariners Weather Log and extrapolation of the tracks since the EPHC stopped issuing advisories on systems before they made landfall. The archives format was significantly changed during 2013 to include non-synoptic best track times, non-developing tropical depressions and wind radii. During February 2016, the NHC released the 1959 Mexico hurricane's reanalysis, which was the first system to be reassessed, using methods developed for the Atlantic reanalysis process.

Extremes

• The strongest recorded Pacific hurricane was Hurricane Patricia (2015), with 1-minute maximum sustained winds of 215 mph (345 km/h) and a minimum barometric pressure of 872 mbar (hPa; 25.75 inHg). This ranks Patricia as the strongest tropical cyclone globally in terms of 1-minute sustained winds and the second strongest globally in terms of barometric pressure.
• Hurricane John (1994) was the farthest-travelling tropical cyclone worldwide, traversing 7,165 mi (13,280 km) in 30 days and 18 hours.
• The 1959 Mexico hurricane was the deadliest Pacific hurricane, causing 1,800 fatalities mostly in Colima and Jalisco.
• There is only one recorded case of a Pacific system reaching California as a hurricane in almost 200 years of observations—the 1858 San Diego Hurricane.

See also

• Atlantic hurricane
• Cordonazo wind
• Tropical cyclone
• Typhoon
• Atlantic hurricane season
• Pacific typhoon climatology
• Pacific typhoon season
• North Indian Ocean tropical cyclone season
• South-West Indian Ocean tropical cyclone season
• Australian region tropical cyclone season
• South Pacific tropical cyclone season
• South Atlantic tropical cyclone
• Mediterranean tropical-like cyclone
• List of Pacific hurricane records

References