Fujiwhara effect

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Typhoon Parma (left) and Melor (right) interacting with each other in the Philippine Sea on October 6, 2009. ParmaMelor AMO TMO 2009279 lrg.jpg
Typhoon Parma (left) and Melor (right) interacting with each other in the Philippine Sea on October 6, 2009.

The Fujiwhara effect, sometimes referred to as the Fujiwara effect, Fujiw(h)ara interaction or binary interaction, is a phenomenon that occurs when two nearby cyclonic vortices orbit each other and close the distance between the circulations of their corresponding low-pressure areas. The effect is named after Sakuhei Fujiwhara, the Japanese meteorologist who initially described the effect. Binary interaction of smaller circulations can cause the development of a larger cyclone, or cause two cyclones to merge into one. Extratropical cyclones typically engage in binary interaction when within 2,000 kilometres (1,200 mi) of one another, while tropical cyclones typically interact within 1,400 kilometres (870 mi) of each other.

Cyclone large scale air mass that rotates around a strong center of low pressure

In meteorology, a cyclone is a large scale air mass that rotates around a strong center of low atmospheric pressure. Cyclones are characterized by inward spiraling winds that rotate about a zone of low pressure. The largest low-pressure systems are polar vortices and extratropical cyclones of the largest scale. Warm-core cyclones such as tropical cyclones and subtropical cyclones also lie within the synoptic scale. Mesocyclones, tornadoes, and dust devils lie within smaller mesoscale. Upper level cyclones can exist without the presence of a surface low, and can pinch off from the base of the tropical upper tropospheric trough during the summer months in the Northern Hemisphere. Cyclones have also been seen on extraterrestrial planets, such as Mars, Jupiter, and Neptune. Cyclogenesis is the process of cyclone formation and intensification. Extratropical cyclones begin as waves in large regions of enhanced mid-latitude temperature contrasts called baroclinic zones. These zones contract and form weather fronts as the cyclonic circulation closes and intensifies. Later in their life cycle, extratropical cyclones occlude as cold air masses undercut the warmer air and become cold core systems. A cyclone's track is guided over the course of its 2 to 6 day life cycle by the steering flow of the subtropical jet stream.

Vortex term in fluid dynamics

In fluid dynamics, a vortex is a region in a fluid in which the flow revolves around an axis line, which may be straight or curved. Vortices form in stirred fluids, and may be observed in smoke rings, whirlpools in the wake of a boat, and the winds surrounding a tropical cyclone, tornado or dust devil.

Orbit gravitationally curved path of an object around a point in outer space; circular or elliptical path of one object around another object

In physics, an orbit is the gravitationally curved trajectory of an object, such as the trajectory of a planet around a star or a natural satellite around a planet. Normally, orbit refers to a regularly repeating trajectory, although it may also refer to a non-repeating trajectory. To a close approximation, planets and satellites follow elliptic orbits, with the central mass being orbited at a focal point of the ellipse, as described by Kepler's laws of planetary motion.

Contents

Description

Diagram of the Fujiwhara effect, showing how 2 tropical cyclones interact with each other. Binaryinteraction.svg
Diagram of the Fujiwhara effect, showing how 2 tropical cyclones interact with each other.

When cyclones are in proximity of one another, their centers will begin orbiting cyclonically (counter-clockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere) [2] about a point between the two systems due to their cyclonic wind circulations. The two vortices will be attracted to each other, and eventually spiral into the center point and merge. It has not been agreed upon whether this is due to the divergent portion of the wind or vorticity advection. [3] When the two vortices are of unequal size, the larger vortex will tend to dominate the interaction, and the smaller vortex will orbit around it. The effect is named after Sakuhei Fujiwhara, the Japanese meteorologist who initially described it in a 1921 paper about the motion of vortices in water. [4] [5]

Wind Flow of gases or air on a large scale

Wind is the flow of gases on a large scale. On the surface of the Earth, wind consists of the bulk movement of air. In outer space, solar wind is the movement of gases or charged particles from the Sun through space, while planetary wind is the outgassing of light chemical elements from a planet's atmosphere into space. Winds are commonly classified by their spatial scale, their speed, the types of forces that cause them, the regions in which they occur, and their effect. The strongest observed winds on a planet in the Solar System occur on Neptune and Saturn. Winds have various aspects, an important one being its velocity ; another the density of the gas involved; another its energy content or wind energy. Wind is also a great source of transportation for seeds and small birds; with time things can travel thousands of miles in the wind.

In continuum mechanics, the vorticity is a pseudovector field that describes the local spinning motion of a continuum near some point, as would be seen by an observer located at that point and traveling along with the flow.

Tropical cyclones

Tropical cyclones can form when smaller circulations within the Intertropical Convergence Zone merge. [6] The effect is often mentioned in relation to the motion of tropical cyclones, although the final merging of the two storms is uncommon. The effect becomes noticeable when they approach within 1,400 kilometres (870 mi) of each other. Rotation rates within binary pairs accelerate when tropical cyclones close within 650 kilometres (400 mi) of each other. [7] Merger of the two systems (or shearing out of one of the pair) becomes realized when they are within 300 kilometres (190 mi) of one another. [8]

Tropical cyclogenesis

Tropical cyclogenesis is the development and strengthening of a tropical cyclone in the atmosphere. The mechanisms through which tropical cyclogenesis occurs are distinctly different from those through which temperate cyclogenesis occurs. Tropical cyclogenesis involves the development of a warm-core cyclone, due to significant convection in a favorable atmospheric environment.

Intertropical Convergence Zone Meteorological phenomenon

The Intertropical Convergence Zone (ITCZ), known by sailors as the doldrums or the calms because of its monotonous, windless weather, is the area where the northeast and southeast trade winds converge. It encircles Earth near the thermal equator, though its specific position varies seasonally. When it lies near the geographic Equator, it is called the near-equatorial trough. Where the ITCZ is drawn into and merges with a monsoonal circulation, it is sometimes referred to as a monsoon trough, a usage more common in Australia and parts of Asia.

Examples

North Atlantic

Hurricane Iris of the 1995 Atlantic hurricane season interacted with Hurricane Humberto, before interacting with and absorbing Tropical Storm Karen on September 3. [9]

Hurricane Iris (1995) Category 2 Atlantic hurricane in 1995

Hurricane Iris was the first of three tropical cyclones to affect the Lesser Antilles in a three-week period, preceding the more destructive hurricanes Luis and Marilyn. The ninth named storm and fifth hurricane of the 1995 Atlantic hurricane season, Iris developed from a tropical wave to the east of the Lesser Antilles on August 22 and attained hurricane status within 30 hours. The hurricane weakened to a tropical storm before crossing the islands of the eastern Caribbean from August 26 through August 28. During that time, Iris became one of four active tropical storms in the Atlantic basin. Earlier it had interacted with Hurricane Humberto, and beginning on August 30, Iris interacted with Tropical Storm Karen. Iris re-intensified into a hurricane and attained peak sustained winds of 110 mph (175 km/h) while moving slowly across the central Atlantic. The hurricane accelerated to the north and absorbed a dissipating Karen on September 3. Iris weakened to a tropical storm and became extratropical on September 4, though its remnants reattained hurricane-force winds before affecting western Europe on September 7.

1995 Atlantic hurricane season hurricane season in the Atlantic Ocean

The 1995 Atlantic hurricane season was a hyperactive Atlantic hurricane season that is generally considered to be the start of an ongoing era of high-activity tropical cyclone formation in the Atlantic basin. It is tied with 1887, 2010, 2011, and 2012 for having the third most number of named storms. The season produced twenty-one tropical cyclones, nineteen named storms, as well as eleven hurricanes and five major hurricanes. The season officially began on June 1 and ended on November 30, dates which conventionally delimit the period of each year when most tropical cyclones develop in the Atlantic basin. The first tropical cyclone, Hurricane Allison, developed on June 2, while the season's final storm, Hurricane Tanya, transitioned into an extratropical cyclone on November 1.

Hurricane Humberto (1995) Category 2 Atlantic hurricane in 1995

Hurricane Humberto was the eighth named storm and the fourth hurricane of the busy 1995 Atlantic hurricane season. It was the first time that the name "Humberto" had been used, replacing the name Hugo, which was retired in 1989. It was a Cape Verde hurricane that never approached land as it tracked across the central Atlantic Ocean.

In 2005, the remnant low of Tropical Depression Thirteen moved northward and then northeastward around a non-tropical low located to the north of the system. It briefly strengthened into Tropical Storm Lee. Thereafter, Lee weakened back to a tropical depression as it moved northeastward and northwestward around the eastern side of the non-tropical low and eventually absorbed the non-tropical low. [10] In the same year, Alpha was absorbed by Wilma.

2005 Atlantic hurricane season Summary of the relevant tropical storms

The 2005 Atlantic hurricane season was the most active Atlantic hurricane season in recorded history, shattering numerous records. The impact of the season was widespread and catastrophic. Its storms caused an estimated total of 3,960 deaths and approximately $180.7 billion in damage, making it the second costliest season on record, surpassed only by the 2017 season.

Tropical Storm Alpha (2005) Atlantic tropical storm in 2005

Tropical Storm Alpha was the twenty-third named storm of the record-breaking 2005 Atlantic hurricane season. Since the twenty-one names from the predetermined A–W list were all used, Alpha was the first tropical storm ever to be given a name from the Greek alphabet. On October 20, Tropical Depression Twenty-five formed from a tropical wave near the Windward Islands. It became a tropical storm on October 23, and reached its peak intensity but weakened again before making landfall in the Dominican Republic that afternoon. Crossing the island of Hispaniola it weakened to a tropical depression, and persisted until October 24, when it dissipated. Its remnant low was absorbed by Hurricane Wilma's large circulation.

Hurricane Wilma Category 5 Atlantic hurricane in 2005

Hurricane Wilma was the most intense tropical cyclone ever recorded in the Atlantic basin, and the second-most intense tropical cyclone recorded in the Western Hemisphere, after Hurricane Patricia in 2015. Part of the record-breaking 2005 Atlantic hurricane season, which included three of the ten most intense Atlantic hurricanes ever, Wilma was the twenty-second storm, thirteenth hurricane, sixth major hurricane, fourth Category 5 hurricane, and the second-most destructive hurricane of the 2005 season. A tropical depression formed in the Caribbean Sea near Jamaica on October 15, headed westward, and intensified into a tropical storm two days later, which abruptly turned southward and was named Wilma. Wilma continued to strengthen, and eventually became a hurricane on October 18. Shortly thereafter, explosive intensification occurred, and in only 24 hours, Wilma became a Category 5 hurricane with wind speeds of 185 mph (298 km/h).

In 2018, Hurricane Helene steered the weaker Tropical Storm Joyce. Helene moved to the north towards Europe while Joyce was spun southward towards the Azores. This interaction may have led to Tropical Storm Joyce's eventual demise.

2018 Atlantic hurricane season Hurricane season in the Atlantic ocean

The 2018 Atlantic hurricane season was the third in a consecutive series of above-average and damaging Atlantic hurricane seasons, featuring 15 named storms, 8 hurricanes, and 2 major hurricanes, which caused a total of over $50.205 billion in damages. The season officially began on June 1, 2018, and ended on November 30, 2018. These dates historically describe the period each year when most tropical cyclones form in the Atlantic basin and are adopted by convention. The formation of Tropical Storm Alberto on May 25, marked the fourth consecutive year in which a storm developed before the official start of the season. The next storm, Beryl, became the first hurricane to form in the eastern Atlantic during the month of July since Bertha in 2008. Chris, upgraded to a hurricane on July 10, became the earliest second hurricane in a season since 2005. No hurricanes formed in the North Atlantic during the month of August, marking the first season since 2013, and the eighth season on record, to do so. On September 5, Florence became the first major hurricane of the season. On September 12, Joyce formed, making 2018 the first season since 2008 to feature four named storms active simultaneously. On October 9, Michael became the second major hurricane of the season, and a day later, it became the first Category 5 hurricane to make landfall in the continental United States since Hurricane Andrew in 1992. With the formation of Oscar on October 26, the season is the first on record to see seven storms that were subtropical at some point in their lifetimes.

Azores Portuguese archipelago in the North Atlantic Ocean

The Azores, officially the Autonomous Region of the Azores, is one of the two autonomous regions of Portugal. It is an archipelago composed of nine volcanic islands in the North Atlantic Ocean about 1,360 km (850 mi) west of continental Portugal, about 1,643 km (1,021 mi) west of Lisbon, in continental Portugal, about 1,507 km (936 mi) northwest of Morocco, and about 1,925 km (1,196 mi) southeast of Newfoundland, Canada.

Northeast Pacific

In 1974, Hurricanes Kirsten and Ione interacted in a Fujiwara interaction, as Ione was pulled northeast, while Kirsten was pulled to the northwest. [11] In the same year, Hurricanes Francesca and Gretchen interacted with each other, until they merged on July 19. [12]

In 1993, Hurricane Hilary absorbed the weaker Tropical Storm Irwin. That same year, Tropical Storm Max was absorbed by a larger Tropical Storm Norma.

In 2001, Hurricane Gil absorbed Tropical Storm Henriette but associated convection totally dissipated during the merger and did not return afterwards.

In 2005, Tropical Storm Lidia was absorbed by Hurricane Max. [13]

In 2014, Hurricane Karina initially traveled west, but was steered back east by an interaction with Hurricane Lowell. It later weakened, and its remnants were later absorbed by Hurricane Marie. [14]

In 2017, Hurricanes Hilary and Irwin interacted. Hilary stopped Irwin's westward movement, and caused Irwin to turn northward. [15]

In 2018, Hurricane John absorbed a nearby weaker storm, Tropical Storm Ileana. [16]

Northwest Pacific

Tropical cyclones Yule and 16W merging, in August 1997 Yule and TD 16W merging.jpg
Tropical cyclones Yule and 16W merging, in August 1997

In September 1994, Typhoon Pat and Tropical Storm Ruth completed a full orbit around their centroid before collapsing into a single cyclone. [17] In August 1997, Tropical Storm Yule merged with Tropical Depression 16W. [18]

In October 2009, Typhoon Parma interacted with Typhoon Melor, affecting the movement of Parma. Parma was moving through the South China Sea but made recurved to the southeast, so it made its second and third landfall over northern Luzon. In addition, due to the interaction with Melor, Parma weakened, becoming a tropical storm by October 4.

In November 2009, Typhoon Nida absorbed Tropical Depression 27W (Urduja) and become a powerful typhoon.

In August 2010, a Fujiwara interaction occurred between Tropical Storm Namtheun and Severe Tropical Storm Lionrock. Namtheun turned southwestward while Lionrock turned eastward. Later, Namtheun weakened into a tropical depression in the Taiwan Strait and was absorbed by Lionrock.

In August 2012, a Fujiwhara interaction occurred between Typhoon Tembin and Bolaven. Tembin was moving west, while Bolaven caused Tembin to turn east, resulting in a counter-clockwise loop of Tembin which caused torrential rain in Southern Taiwan.

In August 2013, Severe Tropical Storm Pewa absorbed Tropical Storm Unala. In August 2016, a Fujiwhara interaction occurred between Typhoons Mindulle and Lionrock. Lionrock was moving west-southwest, while Mindulle caused Lionrock to turn east, resulting in Lionrock being spun to the south of Japan.

In July 2017, Typhoon Noru absorbed Tropical Storm Kulap. Later in the same month, a Fujiwhara interaction occurred between Typhoon Nesat and Tropical Storm Haitang. Nesat caused Haitang to turn northeastward, but the remnants of Nesat were eventually absorbed by Haitang over Fujian.

Southwest Indian Ocean

In 2008, Tropical Cyclone Fame began orbiting Tropical Cyclone Gula with the stronger storm, Gula, absorbing Fame. In 2012, Cyclone Giovanna and Tropical Storm Hilwa interacted in a Fujiwara interaction; Giovanna was pulled to the north, while Hilwa was pulled to the south. In 2019, Severe Tropical Storm Lorna interacted with a tropical low in the Australian region cyclone basin until Lorna absored the smaller tropical low later that day.

South Pacific Ocean

During January 1998, Cyclones Susan and Ron interacted with each other, before Susan absorbed Ron on January 9. [19]

Extratropical cyclones

This satellite loop covering April 26–28, 2011 shows two extratropical cyclones involved in Fujiwhara interaction across the Midwest and Great Lakes.

Binary interaction is seen between nearby extratropical cyclones when within 2,000 kilometres (1,200 mi) of each other, with significant acceleration occurring when the low-pressure areas are within 1,100 kilometres (680 mi) of one another. Interactions between their circulations at the 500 hPa level (18,000 feet above sea level) behave more predictably than their surface circulations. [7] This most often results in a merging of the two low-pressure systems into a single extratropical cyclone, or can less commonly result in a mere change of direction of one or both of the cyclones. [20] The precise results of such interactions depend on factors such as the size of the two cyclones, their distance from each other, and the prevailing atmospheric conditions around them.

See also

Related Research Articles

Subtropical cyclone Meteorological phenomenon

A subtropical cyclone is a weather system that has some characteristics of a tropical and an extratropical cyclone.

1976 Atlantic hurricane season hurricane season in the Atlantic Ocean

The 1976 Atlantic hurricane season featured only one fully tropical storm throughout both the Caribbean Sea and the Gulf of Mexico, a rare occurrence. The 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. However, the first system, a subtropical storm, developed in the Gulf of Mexico on May 21, several days before the official start of the season. The system spawned nine tornadoes in Florida, resulting in about $628,000 (1976 USD) in damage, though impact was minor otherwise. The season was near average, with ten tropical storm forming, of which six became hurricanes. Two of those six became major hurricanes, which are Category 3 or higher on the Saffir–Simpson scale.

1911 Atlantic hurricane season hurricane season in the Atlantic Ocean

The 1911 Atlantic hurricane season was relatively inactive, with only six known tropical cyclones forming in the Atlantic during the summer and fall. There were three suspected tropical depressions, including one that began the season in February and one that ended the season when it dissipated in December. Three storms intensified into hurricanes, two of which attained Category 2 status on the modern-day Saffir–Simpson Hurricane Scale. Storm data is largely based on the Atlantic hurricane database, which underwent a thorough revision for the period between 1911 and 1914 in 2005.

A tropical upper tropospheric trough (TUTT), also known as the mid-oceanic trough,or commonly called as Western Hemisphere or "upper cold low" is a trough situated in upper-level tropics. Its formation is usually caused by the intrusion of energy and wind from the mid-latitudes into the tropics. It can also develop from the inverted trough adjacent to an upper level anticyclone. TUTTs are different from mid-latitude troughs in the sense that they are maintained by subsidence warming near the tropopause which balances radiational cooling. When strong, they can present a significant vertical wind shear to the tropics and subdue tropical cyclogenesis. When upper cold lows break off from their base, they tend to retrograde and force the development, or enhance, surface troughs and tropical waves to their east. Under special circumstances, they can induce thunderstorm activity and lead to the formation of tropical cyclones.

Pacific hurricane mature tropical cyclone that develops within the eastern and central Pacific Ocean

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.

Eye (cyclone) region of mostly calm weather at the center of strong tropical cyclones

The eye is a region of mostly calm weather at the center of strong tropical cyclones. The eye of a storm is a roughly circular area, typically 30–65 km (20–40 miles) in diameter. It is surrounded by the eyewall, a ring of towering thunderstorms where the most severe weather and highest winds occur. The cyclone's lowest barometric pressure occurs in the eye and can be as much as 15 percent lower than the pressure outside the storm.

Central dense overcast

The central dense overcast, or CDO, of a tropical cyclone or strong subtropical cyclone is the large central area of thunderstorms surrounding its circulation center, caused by the formation of its eyewall. It can be round, angular, oval, or irregular in shape. This feature shows up in tropical cyclones of tropical storm or hurricane strength. How far the center is embedded within the CDO, and the temperature difference between the cloud tops within the CDO and the cyclone's eye, can help determine a tropical cyclone's intensity. Locating the center within the CDO can be a problem for strong tropical storms and with systems of minimal hurricane strength as its location can be obscured by the CDO's high cloud canopy. This center location problem can be resolved through the use of microwave satellite imagery.

Extratropical cyclone type of cyclone

Extratropical cyclones, sometimes called mid-latitude cyclones or wave cyclones, are low-pressure areas which, along with the anticyclones of high-pressure areas, drive the weather over much of the Earth. Extratropical cyclones are capable of producing anything from cloudiness and mild showers to heavy gales, thunderstorms, blizzards, and tornadoes. These types of cyclones are defined as large scale (synoptic) low pressure weather systems that occur in the middle latitudes of the Earth. In contrast with tropical cyclones, extratropical cyclones produce rapid changes in temperature and dew point along broad lines, called weather fronts, about the center of the cyclone.

Tropical cyclone Is a rotating storm system

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".

1975 Pacific Northwest hurricane Category 1 Pacific hurricane in 1975

The 1975 Pacific Northwest hurricane was an unusual Pacific tropical cyclone that attained hurricane status farther north than any other Pacific hurricane. It was officially unnamed, with the cargo ship Transcolorado providing vital meteorological data in assessing the storm. The twelfth tropical cyclone of the 1975 Pacific hurricane season, it developed from a cold-core upper-level low merging with the remnants of a tropical cyclone on August 31, well to the northeast of Hawaii. Convection increased as the circulation became better defined, and by early on September 2 it became a tropical storm. Turning to the northeast through an area of warm water temperatures, the storm quickly strengthened, and, after developing an eye, it attained hurricane status late on September 3, while located about 1,200 miles (1,950 km) south of Alaska. After maintaining peak winds for about 18 hours, the storm rapidly weakened, as it interacted with an approaching cold front. Early on September 5, it lost its identity near the coast of Alaska.

Upper tropospheric cyclonic vortex

An upper tropospheric cyclonic vortex is a vortex, or a circulation with a definable center, that usually moves slowly from east-northeast to west-southwest and is prevalent across Northern Hemisphere's warm season. Its circulations generally do not extend below 6,080 metres (19,950 ft) in altitude, as it is an example of a cold-core low. A weak inverted wave in the easterlies is generally found beneath it, and it may also be associated with broad areas of high-level clouds. Downward development results in an increase of cumulus clouds and the appearance of circulation at ground level. In rare cases, a warm-core cyclone can develop in its associated convective activity, resulting in a tropical cyclone and a weakening and southwest movement of the nearby upper tropospheric cyclonic vortex. Symbiotic relationships can exist between tropical cyclones and the upper level lows in their wake, with the two systems occasionally leading to their mutual strengthening. When they move over land during the warm season, an increase in monsoon rains occurs.

Hurricane Kiko (1989) Category 3 Pacific hurricane in 1989

Hurricane Kiko was one of the strongest tropical cyclones to have hit the eastern coast of Mexico's Baja California peninsula during recorded history. The eleventh named storm of the 1989 Pacific hurricane season, Kiko formed out of a large mesoscale convective system on August 25. Slowly tracking northwestward, the storm rapidly intensified into a hurricane early the next day. Strengthening continued until early August 27, when Kiko reached its peak intensity with winds of 120 mph (195 km/h). The storm turned west at this time, and at around 0600 UTC, the storm made landfall near Punta Arena at the southern tip of Baja California Sur. The hurricane rapidly weakened into a tropical storm later that day and further into a tropical depression by August 28, shortly after entering the Pacific Ocean. The depression persisted for another day while tracking southward, before being absorbed by nearby Tropical Storm Lorena. Though Kiko made landfall as a Category 3 hurricane, its impact was relatively minor. Press reports indicated that 20 homes were destroyed and numerous highways were flooded by torrential rains.

Eyewall replacement cycle

Eyewall replacement cycles, also called concentric eyewall cycles, naturally occur in intense tropical cyclones, generally with winds greater than 185 km/h (115 mph), or major hurricanes. When tropical cyclones reach this intensity, and the eyewall contracts or is already sufficiently small, some of the outer rainbands may strengthen and organize into a ring of thunderstorms—an outer eyewall—that slowly moves inward and robs the inner eyewall of its needed moisture and angular momentum. Since the strongest winds are in a cyclone's eyewall, the tropical cyclone usually weakens during this phase, as the inner wall is "choked" by the outer wall. Eventually the outer eyewall replaces the inner one completely, and the storm may re-intensify.

Cold-core low cyclone aloft which has an associated cold pool of air residing at high altitude within the Earths troposphere

A cold-core low, also known as an upper level low or cold-core cyclone, is a cyclone aloft which has an associated cold pool of air residing at high altitude within the Earth's troposphere. It is a low pressure system that strengthens with height in accordance with the thermal wind relationship. If a weak surface circulation forms in response to such a feature at subtropical latitudes of the eastern north Pacific or north Indian oceans, it is called a subtropical cyclone. Cloud cover and rainfall mainly occurs with these systems during the day. Severe weather, such as tornadoes, can occur near the center of cold-core lows. Cold lows can help spawn cyclones with significant weather impacts, such as polar lows, and Kármán vortices. Cold lows can lead directly to the development of tropical cyclones, owing to their associated cold pool of air aloft or by acting as additional outflow channels to aid in further development.

1951 Pacific hurricane season hurricane season in the Pacific ocean

The 1951 Pacific hurricane season ran through the summer and fall of 1951. Nine tropical systems were observed this season.

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