Hurricane Francesca (1970)
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The 1970 Pacific hurricane season was an active
Northern hemisphere The Northern Hemisphere is the half of Earth that is north of the equator. For other planets in the Solar System, north is defined by humans as being in the same celestial sphere, celestial hemisphere relative to the invariable plane of the Solar ...
hurricane A tropical cyclone is a rapidly rotating storm system with a low-pressure area, a closed low-level atmospheric circulation, strong winds, and a spiral arrangement of thunderstorms that produce heavy rain and squalls. Depending on its ...
season, especially during its early months. It officially started on May 15, 1970, in the eastern Pacific Ocean (east of 140°W), and on June 1, 1970, in the central Pacific (between 140°W and the
International Date Line The International Date Line (IDL) is the line extending between the South and North Poles that is the boundary between one calendar day and the next. It passes through the Pacific Ocean, roughly following the 180.0° line of longitude and de ...
). It ended on November 30, 1970, in both regions. These dates conventionally delimit the period of each year when most
tropical cyclogenesis Tropical cyclogenesis is the development and strengthening of a tropical cyclone in the atmosphere. The mechanisms through which tropics, tropical cyclogenesis occur are distinctly different from those through which temperate cyclogenesis occu ...
occurs in these parts of the Pacific. This season had an above average number of storms. There were 21 
tropical cyclone A tropical cyclone is a rapidly rotating storm system with a low-pressure area, a closed low-level atmospheric circulation, strong winds, and a spiral arrangement of thunderstorms that produce heavy rain and squalls. Depending on its locat ...
s, of which 18 reached tropical storm strength. Four storms became hurricanes, of which none reached major hurricane strength. In the central Pacific, one hurricane and one tropical depression formed. One of the depressions crossed the Date Line to become a
typhoon A typhoon is a tropical cyclone that develops between 180° and 100°E in the Northern Hemisphere and which produces sustained hurricane-force winds of at least . This region is referred to as the Northwestern Pacific Basin, accounting for a ...
in the western Pacific. __TOC__


Systems


Hurricane Adele

An area of low pressure lacked strong convection until May 30, when it strengthened into Tropical Depression One-E. On May 31, the system further intensified into Tropical Storm Adele, the first named storm of the season. As Adele tracked westward, it strengthened into a hurricane on June 1 and reached its peak intensity soon afterward. As Adele moved west, a hostile environment caused it to weaken into a tropical storm. Adele further weakened, and it was downgraded into a depression on June 7. It degenerated into an open trough later that day.


Tropical Storm Blanca

The tropical disturbance that became Blanca was first noted on June 8 from satellite pictures. The new disturbance would reach tropical storm strength 24 hours later. Blanca moved in a northwest direction throughout its short life, dissipating on June 12.


Tropical Storm Connie

Near the same location where Hurricane Adele formed two weeks earlier, a disturbance was noted on June 13. The disturbance abruptly became a tropical storm on June 17. The newly named Connie moved slowly to the northwest, reaching a peak intensity of on June 18. Connie started weakening on June 19, finally dissipating on June 21 after stalling from Clarion Island.


Tropical Depression Dolores

A disturbance first noted on June 19 had efficient outflow to be called a tropical depression. Satellite photos taken the same day revealed cloud structure that resembled a tropical storm forming, resulting in the system being called Dolores. The day after, no traces of a storm or of "Dolores" were found by reconnaissance. Post season analysis revealed Dolores to have only been a tropical depression.


Tropical Storm Eileen

A tropical depression formed just off the southern coast of Mexico on June 26. It headed northwestward, reaching storm strength on June 28. The next day, Eileen turned to the northeast, reached a peak of winds, and hit western Mexico.


Hurricane Francesca

Francesca was a Category 2 hurricane which was, for a period of time, obscured by a cap of clouds above the hurricane's eye, distorting the appearance of the hurricane. The precursor disturbance to Hurricane Francesca was first noticed on July 1. The system became a tropical depression later that day and reached tropical storm strength the next day. On July 3, data from a ship indicated winds of near , which indicate a storm of Category 2 strength, near the center of Francesca. The cloud cap, which remained over the hurricane since it first became a hurricane, started to move off the lower clouds around the center of the system around July 5. A center fix was obtained, but the maximum sustained winds were unobtainable from the sea surface because of cloud cover in and around the center. Francesca started weakening on July 6, a fact made clear by reconnaissance which indicated that the system had weakened to a tropical storm. The further weakening was obscured by the cloud cover. The final reconnaissance on the weakening system was reported on July 8, two days before Francesca dissipated.


Tropical Storm Gretchen

Gretchen was first noticed on satellite imagery on July 14. From then on out, Gretchen was a hard storm to predict, leading to large errors in forecasting. The storm dissipated on July 21.


Tropical Storm Helga

The system that became Helga was first noticed on July 16. The next day, reconnaissance found a minimal tropical storm with winds of only . Based on satellite imagery, Helga was believed to be gaining strength as it approached Baja California. At one point during intensification, the storm abruptly started weakening, and on July 19, after stalling less than 118 miles (190 km) south of the tip of Baja California, Helga dissipated.


Tropical Storm Ione 1

A tropical depression developed off the southern coast of Mexico on July 22. A larger intensifying tropical cyclone was spotted by satellite at 2235 on the 24th near 17°N., 111°W. When the expanding circulation of this storm center reached the area of Ione, winds in the latter area decreased and it disappeared abruptly. The second storm, which was also named Ione, moved north-northwestward and began to weaken. Ione reached maximum sustained winds of 45 knots on the 25th near 20. N.,112°W. These winds decreased to 25 knots the next day as storm activity faded rapidly near 16 N., 113°W'. What was unusual about the system was that another tropical storm developed just to its northeast on July 24. That storm, also named Ione, tracked northward, reaching a peak of winds before dissipating on July 25. Operationally, these were considered to be the same storm.


Tropical Storm Ione 2

A tropical depression was discovered near 14°N.,102°W., at 1800 on July 22, but it became disorganized as seen on satellite pictures the next day. Later events indicate it was splitting into two tropical cyclones, both of which were to attain tropical storm strength. The tropical storm first called lone was encountered by the KANIKAWA MARU at 2100 on July 24. That ship was buffeted by 48-kn southeasterly winds and 15-ft seas near 21°N, 107°W. The storm washed out the next day.


Tropical Storm Joyce

A broad, flat low-pressure area persisted south of Baja California after Ione dissipated. On July 29, a small low circulation developed with a center about 120 nautical miles (220 km) south of Manzanillo. The system was given the name Joyce after winds of were reported by a ship. In a similar way to Hurricane Francesca, Tropical Storm Joyce's low level center was unclear due to a cap of cirrus clouds. Joyce reached its peak intensity on July 31 with winds of near before weakening, becoming a depression on August 1. Joyce dissipated on August 4.


Tropical Storm Kristen

Kristen was a loosely organized storm that formed from a disturbance that was causing squalls near the Mexican coast. Tropical storm-force winds were found on August 5. Kristen was tracked by ship reports and satellite pictures. Kristen reached its peak intensity of winds on August 6. The storm dissipated on August 8 while over cold water.


Hurricane Lorraine

Tropical Storm Lorraine, which formed on August 16 south of Mexico, intensified to a hurricane on the 20th. Two days later over open waters, it reached a peak of 95 mph (153 km/h) winds, but estimates from the
Central Pacific Hurricane Center The Central Pacific Hurricane Center (CPHC) of the United States National Weather Service is the official body responsible for tracking and issuing tropical cyclone warnings, watches, advisories, discussions, and statements for the Central Pacif ...
estimated it had winds of 115 mph (185 km/h). Without a chance to strengthen further, Lorraine weakened, finally dissipating on August 27 due to dry air.


Tropical Storm Maggie

A flat low-pressure system appeared in an area of showers to the west-southwest of hurricane Lorraine around 1800 on the 20th. The French refrigerated cargo carrier BIAFRA was buffeted by 38-kn southerly winds, with a barometer reading 1006 mbar, near 13'N, 132'W, by the soon to be named tropical storm Maggie at 0000 on the 21st. Maggie intensified slowly while moving west-northwestward at 9 kn; her maximum winds were estimated at 55 kn at 0300 on the 25th. Maggie passed about 80 mi south of the island of Hawaii on the 25th, dumping torrential rains over the big island. Rainfall amounts ranged from 10 to 15 in on the windward side of the island from the Hamuka coast to Puna and from 1 to 7 in on the leeward side. Maggie was downgraded to a tropical depression at 0900 on the 26th near 18N, 157W. A westward turn saved Hawaii from a direct hit, but Maggie still brought strong surf and heavy yet beneficial rain to the island of
Hawaii Hawaii ( ; ) is an island U.S. state, state of the United States, in the Pacific Ocean about southwest of the U.S. mainland. One of the two Non-contiguous United States, non-contiguous U.S. states (along with Alaska), it is the only sta ...
. There is some evidence that the remains of Maggie redeveloped into Hurricane Dot in the Central Pacific on September 1.


Tropical Storm Norma

Norma was an indirect but essential cause of a flood disaster in Arizona that became known as the "Labor Day Storm of 1970". A depression formed August 31 and rapidly intensified into a tropical storm. Moving rapidly, it headed out to sea before slowing down and weakening. Norma's circulation fed humid unstable air into a large extratropical cyclone over
Arizona Arizona is a U.S. state, state in the Southwestern United States, Southwestern region of the United States, sharing the Four Corners region of the western United States with Colorado, New Mexico, and Utah. It also borders Nevada to the nort ...
. As Norma dissipated, record rains fell over the state from September 4 to September 6. The rains were deadly. There were a total of 22 deaths, including 14 from a
flash flood A flash flood is a rapid flooding of low-lying areas: washes, rivers, dry lakes and depressions. It may be caused by heavy rain associated with a severe thunderstorm, hurricane, or tropical storm, or by meltwater from ice and snow. Flash f ...
on a creek. The damage amounted to over 1 million dollars.


Hurricane Dot

A tropical disturbance, possibly the remnants of Tropical Storm Maggie, became a tropical depression on September 1 to the northwest of Hawaii. It moved to the northwest, coming within miles of the
International Date Line The International Date Line (IDL) is the line extending between the South and North Poles that is the boundary between one calendar day and the next. It passes through the Pacific Ocean, roughly following the 180.0° line of longitude and de ...
and
Midway Island Midway Atoll (colloquial: Midway Islands; ; ) is a atoll in the North Pacific Ocean. Midway Atoll is an insular area of the United States and is an unorganized and unincorporated territory. The largest island is Sand Island, which has housi ...
but remaining in the Central Pacific. Dot turned to the northeast, reaching tropical storm strength on September 2 and hurricane strength September 3 before being absorbed by a cold core system the next day. When Dot became a hurricane at 35° north, it became the highest latitude for a storm to reach hurricane strength east of the International Dateline. This record was soon eclipsed by Hurricane 12 of the 1975 season. A flight flown into Dot also flew into Typhoon Clara.


Tropical Storm Orlene

Tropical Storm Orlene hit Mexico in eastern
Oaxaca Oaxaca, officially the Free and Sovereign State of Oaxaca, is one of the 32 states that compose the political divisions of Mexico, Federative Entities of the Mexico, United Mexican States. It is divided into municipalities of Oaxaca, 570 munici ...
on September 8, having maintained a northeast track for its short lifetime.


Hurricane Patricia

Hurricane Patricia was a strong Category 2 hurricane with winds of 95 mph, Patricia formed on October 4 and dissipated on October 11.


Tropical Storm Rosalie

Rosalie's existence was confirmed on October 21 by observation from a ship. Reconnaissance on the 22nd reported a central pressure of 1006 mb. After a slight regeneration on the 23rd, Rosalie began rapid dissipation, finally dissipating on the 23rd.


Tropical Storm Selma

The final storm of the season, Tropical Storm Selma, developed on November 1 to the southwest of Mexico. It meandered to the north, turning to the northeast and northwest before heading southeastward and dissipating on November 8.


Storm names

The following list of names was used for named storms that formed in the North Pacific Ocean east of 140°W in 1970. It was the same list used in the 1966 season, with the exception of ''Kristen'', which replaced ''Kirsten''. Storms were named ''Kristen'', ''Norma'', ''Orlene'', ''Patricia'', ''Rosalie'', and ''Selma'' for the first time this season. The name ''Kristen'' was later respelled as ''Kirsten'' for 1974. One named storm, listed below, formed in the North Pacific between 140°W and the
International Date Line The International Date Line (IDL) is the line extending between the South and North Poles that is the boundary between one calendar day and the next. It passes through the Pacific Ocean, roughly following the 180.0° line of longitude and de ...
in 1970. At the time, storm names within this region were assigned by the
Joint Typhoon Warning Center The Joint Typhoon Warning Center (JTWC) is a joint United States Navy – United States Air Force command in Pearl Harbor, Hawaii. The JTWC is responsible for the issuing of tropical cyclone warnings in the North-West Pacific Ocean, South P ...
on
Guam Guam ( ; ) is an island that is an Territories of the United States, organized, unincorporated territory of the United States in the Micronesia subregion of the western Pacific Ocean. Guam's capital is Hagåtña, Guam, Hagåtña, and the most ...
. Named storms in the table above that crossed into the area during the season are noted (*).


Retirement

The name ''Adele'' was later retired without explanation. It was replaced with ''Aletta'' for the 1974 season.


Administrative changes

This is the first season that the
Redwood City Redwood City is a city on the San Francisco Peninsula in the Bay Area of Northern California, approximately south of San Francisco and northwest of San Jose. The city's population was 84,292 according to the 2020 census. The Port of Redwo ...
-based
Eastern Pacific Hurricane Center The Eastern Pacific Hurricane Center was formerly the center responsible for forecasting Pacific hurricanes in the eastern north Pacific east of 140°W. It was part of the Weather Bureau Forecast Office San Francisco and was based in Redwood City ...
started issuing advisories on tropical cyclones in the eastern north Pacific. It replaced the previous forecaster, Fleet Weather Central. Also. the
Central Pacific Hurricane Center The Central Pacific Hurricane Center (CPHC) of the United States National Weather Service is the official body responsible for tracking and issuing tropical cyclone warnings, watches, advisories, discussions, and statements for the Central Pacif ...
started to issue advisories on tropical cyclones in its area of responsibility this season. It replaced the Joint Hurricane Warning Center.


See also

*
List of Pacific hurricanes This is a list of notable Pacific hurricanes, subdivided by reason for notability. Notability means that it has met some criterion or achieved some statistic, or is part of a top ten for some superlative. It includes lists and rankings of Pacific ...
*
Pacific hurricane season A Pacific hurricane is a tropical cyclone that develops within the northeastern 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: t ...
*
1970 Atlantic hurricane season The 1970 Atlantic hurricane season officially began on June 1 and lasted until November 30. These dates conventionally delimit the period of each year when most tropical cyclones form in the Atlantic basin. The season was fairly ave ...
*
1970 Pacific typhoon season The 1970 Pacific typhoon season has no official bounds; it ran year-round in 1970, but most tropical cyclones tend to form in the northwestern Pacific Ocean between June and December. These dates conventionally delimit the period of each year wh ...
*
1970 North Indian Ocean cyclone season The 1970 North Indian Ocean cyclone season was an extremely devastating North Indian cyclone season. The 1970 season saw a total of seven cyclonic storms, of which three developed into severe cyclonic storms. The Bay of Bengal was more active ...
* Australian cyclone seasons: 1969–70, 1970–71 * South Pacific cyclone seasons: 1969–70, 1970–71 * South-West Indian Ocean cyclone seasons: 1969–70, 1970–71


References


1970 CPHC Archive
accessed November 17, 2005
NOAA Monthly Weather Review
accessed November 17, 2005

accessed November 17, 2005


External links


ATCR Eastern Pacific summary
{{DEFAULTSORT:1970 Pacific Hurricane Season Pacific hurricane seasons Articles which contain graphical timelines