Chapter 80

(Excerpted from Wikipedia. With a few personal old wives tales added.)

A Pacific hurricane is a tropical cyclone that develops within the eastern and central Pacific Ocean to the east of 180°W, north of the equator. For tropical cyclone warning purposes, the northern Pacific is divided into three regions: the eastern (North America to 140°W), central (140°E to 180°), and western (180° to 100°E), while the southern Pacific is divided into 2 sections, the Australian region (90E to 160°E), the southern Pacific basin between (160°E to 120°W). Identical phenomena in the western north Pacific are called typhoons. This separation between the two basins is convenient, however, as tropical cyclones rarely form in the central north Pacific and few cross the dateline.

Documentation of Pacific hurricanes date to the Spanish colonization of Mexico, when 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° to 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 from 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 was 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. The HURDAT database began keeping records in 1949. Between 1970 and 1975, advisories for systems in the eastern Pacific basins were initiated by the Eastern Pacific Hurricane Center (EPHC) as part of the National Weather Service (NWS) office in San Francisco, California. At that time, the advisories released were written in cooperation with the United States Navy Fleet Weather Center in Alameda and the Air Force Hurricane Liaison Officer at the McClellan Air Force Base. Following the move of the hurricane center to Redwood City in 1976, track files were created and altered by Arthur Pike and were later re-modified following the release of a study in 1980. The National Hurricane Center (NHC) extended its authority to the EPHC in 1988, and subsequently began maintaining the tracks.

Wasn't that sweet of them?

The presence of a semi-permanent high-pressure area known as the North Pacific High in the eastern Pacific is a dominant factor against formation of tropical cyclones in the winter, as the Pacific High results in wind shear that causes environmental conditions for tropical cyclone formation to be not conductive.

IThe Intertropical Convergence Zone departs southward in mid-May permitting the formation of the earliest tropical waves, coinciding with the start of the eastern Pacific hurricane season on May 15.

In the eastern Pacific, Hurricane season runs between May 15 and November 30 each year. These dates encompass the vast majority of tropical cyclone activity in this region.

We were early ... so was our storm.

This area is, on average, the second-most active basin in the world.

Most east Pacific hurricanes originate from a tropical wave that drifts westward across the intertropical convergence zone, and across northern parts of South America.

Once it reaches the Pacific, a surface low begins to develop, however, with only little or no convection. After reaching the Pacific, it starts to move north-westward and eventually west.

By that time, it develops convection and thunderstorm activity from the warm ocean temperatures but remains disorganized. Once it becomes organized, it becomes a tropical depression. Formation usually occurs from south of the Gulf of Tehuantepec to south of Baja California with a more westerly location earlier in the season.

In the eastern Pacific, development is more centered than anywhere. Most tropical cyclones in the eastern Pacific reach their peak strength as a strong tropical storm due to strong shear. If wind shear is low, storms can undergo major intensification as a result of very warm oceans, becoming a major hurricane. Major hurricanes weaken once they reach unfavorable areas for a tropical cyclone formation, and most of them do an eyewall replacement and weaken. Their remnants sometimes reach Hawaii and cause showers there.

There are a few types of Pacific hurricane tracks: one is a westerly track, another moves north-westward along Baja California and another moves north.