|Tropical Storm (SSHWS/NWS)|
|Formed||September 27, 1990|
|Dissipated||October 3, 1990|
|Highest winds|| 1-minute sustained:65 mph (100 km/h)|
|Lowest pressure||994 mbar (hPa); 29.35 inHg|
|Areas affected||Baja California Sur, Mainland Mexico, Texas|
|Part of the 1990 Pacific hurricane season|
Tropical Storm Rachel was the only tropical cyclone to make landfall during the 1990 Pacific hurricane season. The twenty-fourth tropical depression and eighteenth named storm, Rachel developed on September 27 from a tropical wave southwest of mainland Mexico. After becoming a tropical depression, the system tracked slowly southwestward and eventually curved northwestward. The depression intensified into a tropical storm after three days and was named Rachel by the National Hurricane Center. Rachel continued to steadily strengthen, and peaked as a strong 65 mph (100 km/h) tropical storm on October 2. After attaining peak intensity, Rachel re-curved to make a landfall in southern Baja California Sur and again in the Mexican Mainland on October 3. The storm produced heavy rainfall across northern Mexico and the Southwestern United States. Thousands of people were left homeless and 18 fatalities were reported.
A tropical cyclone is a rapidly rotating storm system characterized by a low-pressure center, a closed low-level atmospheric circulation, strong winds, and a spiral arrangement of thunderstorms that produce heavy rain. Depending on its location and strength, a tropical cyclone is referred to by different names, including hurricane, typhoon, tropical storm, cyclonic storm, tropical depression, and simply cyclone. A hurricane is a tropical cyclone that occurs in the Atlantic Ocean and northeastern Pacific Ocean, and a typhoon occurs in the northwestern Pacific Ocean; in the south Pacific or Indian Ocean, comparable storms are referred to simply as "tropical cyclones" or "severe cyclonic storms".
The 1990 Pacific hurricane season was a very active season which observed 21 named storms within the basin. The season also produced the fourth highest ACE index value on record. The season was officially started on May 15 in the eastern Pacific, and on June 1 in the central Pacific, and lasted until November 30. These dates conventionally delimit the period of each year when most tropical cyclones form in the northeastern Pacific Ocean. However, these bounds were slightly exceeded when Hurricane Alma formed on May 12.
Tropical cyclones and subtropical cyclones are named by various warning centers to provide ease of communication between forecasters and the general public regarding forecasts, watches, and warnings. The names are intended to reduce confusion in the event of concurrent storms in the same basin. Generally once storms produce sustained wind speeds of more than 33 knots, names are assigned in order from predetermined lists depending on which basin they originate. However, standards vary from basin to basin: some tropical depressions are named in the Western Pacific, while tropical cyclones must have a significant amount of gale-force winds occurring around the centre before they are named in the Southern Hemisphere.
The origins of Rachel can be traced back to a tropical wave that moved off the west coast Africa in mid-September 1990. 22. The thunderstorm activity became more concentrated two days later. Dvorak classifications, a technique used to estimate a tropical cyclone's intensity, began late September 25.It moved westward into the Caribbean Sea without significant development. Poorly organized, the wave entered the Eastern Pacific on overnight September
Tropical waves, easterly waves, or tropical easterly waves, also known as African easterly waves in the Atlantic region, are a type of atmospheric trough, an elongated area of relatively low air pressure, oriented north to south, which moves from east to west across the tropics, causing areas of cloudiness and thunderstorms. West-moving waves can also form from the tail end of frontal zones in the subtropics and tropics, and may be referred to as easterly waves, but these waves are not properly called tropical waves; they are a form of inverted trough sharing many characteristics with fully tropical waves. All tropical waves form in the easterly flow along the equatorward side of the subtropical ridge or belt of high pressure which lies north and south of the Intertropical Convergence Zone (ITCZ). Tropical waves are generally carried westward by the prevailing easterly winds along the tropics and subtropics near the equator. They can lead to the formation of tropical cyclones in the north Atlantic and northeastern Pacific basins. A tropical wave study is aided by Hovmöller diagrams, a graph of meteorological data.
The Caribbean Sea is a sea of the Atlantic Ocean in the tropics of the Western Hemisphere. It is bounded by Mexico and Central America to the west and south west, to the north by the Greater Antilles starting with Cuba, to the east by the Lesser Antilles, and to the south by the north coast of South America.
A Pacific hurricane is a mature 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, central, and western, while the southern Pacific is divided into 2 sections, the Australian region and the southern Pacific basin between 160°E and 120°W. 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.
Early on September 27, the twenty-fourth tropical depression of the season had developed; however, operationally it was not warned upon until the system was located 540 mi (870 km) south of Baja California Sur on September 30. Post-analysis later confirm that Rachel was already a minimal tropical storm by that time. Although convection initially remained displaced from the center, Rachel steadily intensified. Early on September 30, the National Hurricane Center (NHC) operationally upgraded the depression into Tropical Storm Rachel. While intensifying, an upper-level trough over California allowed Rachel to re-curve towards Mexico. On October 2, it reached its peak intensity of 65 mph (100 km/h) and a minimum pressure of 994 mbar (hPa; 29.35 inHg).
Baja California Sur, officially the Estado Libre y Soberano de Baja California Sur, is the second-smallest Mexican state by population and the 31st admitted state of the 31 states which, with Mexico City, make up the 32 Federal Entities of Mexico.
Atmospheric convection is the result of a parcel-environment instability, or temperature difference layer in the atmosphere. Different lapse rates within dry and moist air masses lead to instability. Mixing of air during the day which expands the height of the planetary boundary layer leads to increased winds, cumulus cloud development, and decreased surface dew points. Moist convection leads to thunderstorm development, which is often responsible for severe weather throughout the world. Special threats from thunderstorms include hail, downbursts, and tornadoes.
The National Hurricane Center (NHC) is the division of the United States' National Weather Service responsible for tracking and predicting tropical weather systems between the Prime Meridian and the 140th meridian west poleward to the 30th parallel north in the northeast Pacific Ocean and the 31st parallel north in the northern Atlantic Ocean. The agency, which is co-located with the Miami branch of the National Weather Service, is situated on the campus of Florida International University in University Park, Florida.
After maintaining its intensity for 24 hours, Rachel made landfall at peak intensity near the southern tip of Baja California Sur. 3. By that time, the winds had decreased to 30 mph (45 km/h). The remnants of Rachel entered the United States, and were last noted over Texas.Strong wind shear prevented additional intensification, despite moving into the warm waters of the Gulf of California. After weakening slightly, Rachel made a second landfall midway between Las Mochis and Culiacán. Upon moving inland, the system rapidly weakened as the forward speed increased. Rachel dissipated several hours later on October
Wind shear, sometimes referred to as wind gradient, is a difference in wind speed or direction over a relatively short distance in the atmosphere. Atmospheric wind shear is normally described as either vertical or horizontal wind shear. Vertical wind shear is a change in wind speed or direction with change in altitude. Horizontal wind shear is a change in wind speed with change in lateral position for a given altitude.
The Gulf of California is a marginal sea of the Pacific Ocean that separates the Baja California Peninsula from the Mexican mainland. It is bordered by the states of Baja California, Baja California Sur, Sonora, and Sinaloa with a coastline of approximately 4,000 km (2,500 mi). Rivers which flow into the Gulf of California include the Colorado, Fuerte, Mayo, Sinaloa, Sonora, and the Yaqui. The gulf's surface area is about 160,000 km2 (62,000 sq mi). Depth soundings in the gulf have ranged from fording depth at the estuary near Yuma, Arizona, to in excess of 3,000 meters (9,800 ft) in the deepest parts.
Culiacán is a city in northwestern Mexico. It is the largest city in and the capital of the state of Sinaloa. It is also the seat of Culiacán Municipality. It had an urban population of 785,800 in 2015 while 905,660 lived in the entire municipality. While the municipality has a total area of 4,758 km2 (1,837 sq mi), the city itself is considerably smaller, measuring only 65 km2 (25 sq mi).
Prior to the arrival of Rachel, the Mexican government issued a tropical storm watch for southern Baja California Sur, encompassing areas south of La Paz on October 1. As Rachel moved closer to the area, the watch was replaced with a tropical storm warning. In the mainland, a tropical storm watch was issued for the state of Sinaloa south of Los Mmochis. Six hours later, the watches was replaced with a tropical storm warning. By the end of October 2, all the watches and warnings were discontinued.
Tropical cyclone warnings and watches are two levels of alert issued by national weather forecasting bodies to coastal areas threatened by the imminent approach of a tropical cyclone of tropical storm or hurricane intensity. They are notices to the local population and civil authorities to make appropriate preparation for the cyclone, including evacuation of vulnerable areas where necessary. It is important that interests throughout the area of an alert make preparations to protect life and property, and do not disregard it on the strength of the detailed forecast track. Tropical cyclones are not points, and forecasting their track remains an uncertain science.
La Paz is the capital city of the Mexican state of Baja California Sur and an important regional commercial center. The city had a 2015 census population of 244,219 inhabitants, making it the most populous city in the state. Its metropolitan population is somewhat larger because of the surrounding towns, such as El Centenario, Chametla and San Pedro. It is in La Paz Municipality, which is the fourth-largest municipality in Mexico in geographical size and reported a population of 290,286 inhabitants on a land area of 20,275 km2 (7,828 sq mi).
Sinaloa, officially the Free and Sovereign State of Sinaloa, is one of the 31 states which, with the Federal District, compose the 32 Federal Entities of Mexico. It is divided into 18 municipalities and its capital city is Culiacán Rosales.
The two highest rainfall totals were 9.85 in (250 mm) and 6.5 in (170 mm) at Santa Anita and San Jose Del Cobe, near the southern tip of Baja California Sur. Two weather stations in Mexico reported barometric pressure of 1005 and 1006 mbar (hPa; 29.68 and 29.71 inHg) during the passage of Rachel. In all, precipitation was measured at 996 different places across the country. Throughout northern Mexico, significant flooding was reported with the worst effects felt in the states of Nuevo Leon, Coahuila and Durango. Thousands were homeless, and 18 people died. In Monterrey, rescue workers freed dozens of trapped people.
Mexico, officially the United Mexican States, is a country in the southern portion of North America. It is bordered to the north by the United States; to the south and west by the Pacific Ocean; to the southeast by Guatemala, Belize, and the Caribbean Sea; and to the east by the Gulf of Mexico. Covering almost 2,000,000 square kilometres (770,000 sq mi), the nation is the fifth largest country in the Americas by total area and the 13th largest independent state in the world. With an estimated population of over 120 million people, the country is the eleventh most populous state and the most populous Spanish-speaking state in the world, while being the second most populous nation in Latin America after Brazil. Mexico is a federation comprising 31 states and Mexico City, a special federal entity that is also the capital city and its most populous city. Other metropolises in the state include Guadalajara, Monterrey, Puebla, Toluca, Tijuana and León.
Coahuila, formally Coahuila de Zaragoza, officially the Free and Sovereign State of Coahuila de Zaragoza, is one of the 31 states which, along with Mexico City, compose the 32 Federal Entities of Mexico.
Durango, officially Free and Sovereign State of Durango, is a state in northwest Mexico. With a population of 1,632,934, Durango has Mexico's second-lowest population density, after Baja California Sur. The city of Victoria de Durango is the state's capital, named after the first president of Mexico, Guadalupe Victoria.
The moisture associated with the Rachel and a cold front produced rainfall in Arizona, New Mexico, and western Texas, while it was located southwest of Baja California Sur. After Rachel had dropped heavy rains, a flash flood watch was issued for several counties in New Mexico on October 1, where rainfall had reportedly been 2 in (51 mm) since the last day of September. The remnants of the storm produced additional precipitation across the state. Heavy rains fell on almost all of western Texas, and a flash flood warning had been issued after some areas experienced rainfall over 1 in (25 mm). With heavy rains falling in the western portion of Texas, some roads were washed out, especially in Big Bend National Park and Lubbock; several car accidents were also reported on the roads. Several locations in Texas measured at least 0.5 in (13 mm) of rain, and the highest amount of rainfall was 1.5 in (38 mm) in Lubbock.
The 1990 Atlantic hurricane season was the most active Atlantic hurricane season since 1969. It officially began on June 1, 1990, and lasted until November 30, 1990. These dates conventionally delimit the period of each year when most tropical cyclones form in the Atlantic basin. One tropical depression did form before the season officially started, however.
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The 1995 Pacific hurricane season was the least active Pacific hurricane season since 1979. Of the eleven tropical cyclones that formed during the season, four affected land, with the most notable storm of the season being Hurricane Ismael, which killed at least 116 people in Mexico. The strongest hurricane in the season was Hurricane Juliette, which reached peak winds of 150 mph (240 km/h), but did not significantly affect land. Hurricane Adolph was an early-season Category 4 hurricane. Hurricane Henriette brushed the Baja California Peninsula in early September.
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Hurricane Waldo was a Pacific hurricane that caused significant flooding in Kansas during October 1985. After developing into a tropical depression on October 7, it steadily intensified, becoming a tropical storm within a day. Waldo reached hurricane intensity on October 8. After peaking as a moderate Category 2 hurricane on the Saffir–Simpson hurricane scale, it re-curved to the east, making landfall at peak intensity near Culiacán. Afterward, it rapidly dissipated. In all, Waldo caused moderate damage in Sonora. The remnants of the storm combined with a cold front over the Great Plains. Significant flooding and one death was recorded in Kansas. Many rivers and creeks overflowed its banks.
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