Post-tropical cyclone

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A post-tropical cyclone is a former tropical cyclone. [1] Two classes of post-tropical cyclones are:

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".


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.

Weather front boundary separating two masses of air of different densities

A weather front is a boundary separating two masses of air of different densities, and is the principal cause of meteorological phenomena outside the tropics. In surface weather analyses, fronts are depicted using various colored triangles and half-circles, depending on the type of front. The air masses separated by a front usually differ in temperature and humidity.

Not all systems fall into the above two classes. According to the guideline, a system without frontal characteristics but with maximum winds above 34 knots may not be designated as a remnant low. It should be merely described as post-tropical. [4] A few examples falling into this grey area are listed below.

Hurricane Celia (2010) Category 5 Pacific hurricane in 2010

Hurricane Celia was a powerful, early-season Category 5 tropical cyclone that existed over the open waters of the eastern Pacific Ocean during late June 2010. Forming out of a tropical wave about 370 mi (595 km) southeast of Acapulco, Mexico on June 18, Celia quickly organized as deep convection consolidated around the center, attaining hurricane status by June 20. Over the following days, the hurricane's winds fluctuated as wind shear impeded significant development hindering it from becoming potentially dangerous. Once this shear lightened on June 24, the storm rapidly intensified to attain its peak strength with winds of 160 mph (260 km/h) and an estimated barometric pressure of 921 mbar. Not long after reaching this strength, wind shear increased and the system entered a dry, stable environment. Over the following 42 hours, Hurricane Celia's sustained winds decreased to tropical storm force and the system began to stall over the open ocean by June 27. Despite highly unfavorable conditions, the storm managed to retain tropical storm status through June 28 and degenerated into a non-convective remnant low that evening. The remnants of Celia drifted northward, completing a counter-clockwise loop, and dissipated on June 30.

Hurricane Sandy Category 3 Atlantic hurricane in 2012

Hurricane Sandy was the deadliest and most destructive hurricane of the 2012 Atlantic hurricane season. Inflicting nearly $70 billion in damage, it was the second-costliest hurricane on record in the United States until surpassed by Hurricanes Harvey and Maria in 2017. The eighteenth named storm, tenth hurricane, and second major hurricane of the year, Sandy was a Category 3 storm at its peak intensity when it made landfall in Cuba. While it was a Category 2 hurricane off the coast of the Northeastern United States, the storm became the largest Atlantic hurricane on record. At least 233 people were killed along the path of the storm in eight countries.

Hurricane Joaquin Category 4 Atlantic hurricane in 2015

Hurricane Joaquin was a powerful tropical cyclone that devastated several districts of the Bahamas and caused damage in the Turks and Caicos Islands, parts of the Greater Antilles, and Bermuda. It was also the strongest Atlantic hurricane of non-tropical origin in the satellite era. The tenth named storm, third hurricane, and second major hurricane of the 2015 Atlantic hurricane season, Joaquin evolved from a non-tropical low to become a tropical depression on September 28, well southwest of Bermuda. Tempered by unfavorable wind shear, the depression drifted southwestward. After becoming a tropical storm the next day, Joaquin underwent rapid intensification, reaching hurricane status on September 30 and Category 4 major hurricane strength on October 1. Meandering over the southern Bahamas, Joaquin's eye passed near or over several islands. On October 3, the hurricane weakened somewhat and accelerated to the northeast. Abrupt re-intensification ensued later that day, and Joaquin acquired sustained winds of 155 mph (250 km/h), just short of Category 5 strength.

However, there has been an occasion that the United States National Hurricane Center violated the definition and designated Calvin (2011) as a 35-knot remnant low. [11]

United States Federal republic in North America

The United States of America (USA), commonly known as the United States or America, is a country comprising 50 states, a federal district, five major self-governing territories, and various possessions. At 3.8 million square miles, the United States is the world's third or fourth largest country by total area and is slightly smaller than the entire continent of Europe's 3.9 million square miles. With a population of over 327 million people, the U.S. is the third most populous country. The capital is Washington, D.C., and the largest city by population is New York City. Forty-eight states and the capital's federal district are contiguous in North America between Canada and Mexico. The State of Alaska is in the northwest corner of North America, bordered by Canada to the east and across the Bering Strait from Russia to the west. The State of Hawaii is an archipelago in the mid-Pacific Ocean. The U.S. territories are scattered about the Pacific Ocean and the Caribbean Sea, stretching across nine official time zones. The extremely diverse geography, climate, and wildlife of the United States make it one of the world's 17 megadiverse countries.

National Hurricane Center division of the United States National Weather Service

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.

Also, if a tropical cyclone degenerates into a tropical wave or trough, then it does not qualify as a post-tropical cyclone. It would be referred as the "remnants of (tropical cyclone name)".

Tropical wave type of atmospheric trough

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.

Trough (meteorology) elongated region of low atmospheric pressure

A trough is an elongated (extended) region of relatively low atmospheric pressure, often associated with fronts. Troughs may be at the surface, or aloft, or both under various conditions. Most troughs bring clouds, showers, and a wind shift, particularly following the passage of the trough. This results from convergence or "squeezing" which forces lifting of moist air behind the trough line.

Météo-France classifies systems in the South-West Indian Ocean undergoing an extratropical transition or losing tropical characteristics as “post-tropical depressions”, since the 2012–13 cyclone season. They would be re-classified as extratropical depressions after completing the process. [12]


A post-tropical cyclone is formed when the typical characteristics of a tropical cyclone are replaced with those of extratropical cyclones, otherwise known as extratropical transition. [13] After the initial formation, a post-tropical cyclone has the potential to gain strength and intensity by forming an extratropical storm. [13] If a post-tropical cyclone does become an extratropical storm, it will eventually decay through the process of occlusion. [14]


The re-intensification of a post-tropical cyclone can cause dangerous conditions in North Atlantic shipping routes with high seas and winds comparable to those of hurricanes. [13]


The terminology was initiated by Canadian Hurricane Centre in 1998 during Tropical Storm Bonnie. [15] In 2008, the National Hurricane Center used this term for Tropical Storm Laura to address the limitation of the two classes (extratropical/remnant low) mentioned above. [16] The term was later adopted by the National Weather Service on May 15, 2010. [4]


The Bureau of Meteorology in Australia refers a former tropical cyclone as an "ex-tropical cyclone".[ citation needed ] An example is ex-tropical cyclone Oswald.

Related Research Articles

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 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.

Subtropical cyclone

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

The synoptic scale in meteorology is a horizontal length scale of the order of 1000 kilometers or more. This corresponds to a horizontal scale typical of mid-latitude depressions. Most high and low-pressure areas seen on weather maps such as surface weather analyses are synoptic-scale systems, driven by the location of Rossby waves in their respective hemisphere. Low-pressure areas and their related frontal zones occur on the leading edge of a trough within the Rossby wave pattern, while high-pressure areas form on the back edge of the trough. Most precipitation areas occur near frontal zones. The word synoptic is derived from the Greek word συνοπτικός, meaning seen together.

Tropical cyclones are unofficially ranked on one of five tropical cyclone intensity scales, according to their maximum sustained winds and which tropical cyclone basin(s) they are located in. Only a few scales of classifications are used officially by the meteorological agencies monitoring the tropical cyclones, but some alternative scales also exist, such as accumulated cyclone energy, the Power Dissipation Index, the Integrated Kinetic Energy Index, and the Hurricane Severity Index.

Rapid intensification

Rapid intensification is a meteorological condition that occurs when a tropical cyclone intensifies dramatically in a short period of time. The United States National Hurricane Center (NHC) defines rapid intensification as an increase in the maximum 1-min sustained winds of a tropical cyclone of at least 30 knots in a 24-hour period.

Tropical Storm Nicholas Atlantic tropical storm in 2003

Tropical Storm Nicholas was a long-lived tropical storm in October and November of the 2003 Atlantic hurricane season. Forming from a tropical wave on October 13 in the central tropical Atlantic Ocean, Nicholas slowly developed due to moderate levels of wind shear throughout its lifetime. Deep convection slowly organized, and Nicholas attained a peak intensity of 70 mph (110 km/h) on October 17. After moving west-northwestward for much of its lifetime, it turned northward and weakened due to increasing shear. The storm again turned to the west and briefly restrengthened, but after turning again to the north Nicholas transitioned to an extratropical cyclone on October 24. As an extratropical storm, Nicholas executed a large loop to the west, and after moving erratically for a week and organizing into a tropical low, it was absorbed by a non-tropical low. The low continued westward, crossed Florida, and ultimately dissipated over the Gulf Coast of the United States on November 5.

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.

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.

2011 Pacific hurricane season hurricane season in the Pacific Ocean

The 2011 Pacific hurricane season was a below-average Pacific hurricane season and was the first season since 2009 that featured no depressions or named storms in the month of May. It had six major hurricanes which was above average for a Pacific hurricane season. The season officially started on May 15, 2011, for the eastern Pacific, and started on June 1, 2011, for the central Pacific, both of which ended on November 30, 2011. These dates conventionally delimit the period of each year when most tropical cyclones form in the Pacific basin. A total of 11 named storms were observed, which is below average.

2012 Pacific hurricane season hurricane season in the Pacific Ocean

The 2012 Pacific hurricane season was a moderately active Pacific hurricane season that saw an unusually high number of tropical cyclones pass west of the Baja California Peninsula. The season officially started on May 15 in the eastern Pacific, and on June 1 in the central Pacific, and ended on November 30; these dates conventionally delimit the period during which most tropical cyclones form in the northeastern Pacific Ocean. However, with the formation of Tropical Storm Aletta on May 14 the season slightly exceeded these bounds.

Tropical Storm Laura (2008) Atlantic tropical storm in 2008

Tropical Storm Laura was a large but short-lived tropical cyclone that developed over the north-central Atlantic Ocean in late September during the 2008 Atlantic hurricane season. The 12th named storm of the season, Laura formed out of a large extratropical area of low pressure located about 1015 miles (1635 km) west of the Azores on September 29. Laura slowly developed tropical characteristics throughout the day as it moved over warmer waters. On the afternoon of September 30, Laura had acquired enough tropical characteristics to be designated a Tropical Storm. Shortly after being declared tropical, Laura began to undergo an extratropical transition, which did not fully take place until the morning of October 1. Laura degenerated into a post-tropical cyclone later that morning, and the final advisory by the National Hurricane Center was issued. The remnants of Laura contributed to heavy rainfall and power outages in the British Isles, the Netherlands, and Norway on October 5 to 8.

Tropical Storm Grace (2009) Atlantic tropical storm in 2009

Tropical Storm Grace holds the record for being the farthest northeast forming tropical cyclone in the Atlantic basin. The seventh named storm of the slightly below average 2009 Atlantic hurricane season, Grace formed from an extratropical cyclone over the Azores on October 4. It strengthened to attain peak sustained winds of 65 mph (100 km/h) and developed an eye-like feature, although cold sea surface temperatures inhibited the development of thunderstorm activity near the center. The storm lost its tropical characteristics on October 6, though the remnants merged with a separate system near the British Isles.

2013 Atlantic hurricane season hurricane season in the Atlantic Ocean

The 2013 Atlantic hurricane season was a well below average Atlantic hurricane season and the first since 1994 with no major hurricanes. It was also the first season since 1968 with no storms of at least Category 2 intensity on the Saffir–Simpson hurricane wind scale. The first tropical cyclone of this hurricane season, Andrea, developed on June 5, while the final cyclone, an unnamed subtropical storm, dissipated on December 7. Throughout the year, only two storms—Humberto and Ingrid—reached hurricane intensity; this was the lowest seasonal total since 1982.

Hurricane Epsilon Category 1 Atlantic hurricane in 2005

Hurricane Epsilon was the final of fifteen hurricanes within the record-breaking 2005 Atlantic hurricane season. Originating from a cold front beneath an upper-level low, Epsilon formed on November 29 about 915 mi (1470 km) east of Bermuda. Initially, the National Hurricane Center (NHC) forecast the storm to transition into an extratropical cyclone within five days, due to conditions unfavorable for significant intensification. Epsilon continually defied forecasts, at first due to an unexpected loop to the southwest, and later due to retaining its strength despite cold waters and strong wind shear.

Glossary of tropical cyclone terms

The following is a glossary of tropical cyclone terms.

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 $49.975 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.

2018 Pacific hurricane season Period of formation of tropical cyclones in the Eastern Pacific Ocean in 2018

The 2018 Pacific hurricane season produced the highest accumulated cyclone energy (ACE) value on record in the Eastern Pacific basin. With 23 named storms, it was the fourth-most active season on record, tied with 1982. The season officially began on May 15 in the eastern Pacific, and on June 1 in the central Pacific; they both ended on November 30. These dates conventionally delimit the period of each year when most tropical cyclones form in the Pacific basin, as illustrated when the first tropical depression formed on May 10.

Tropical Storm Gordon (2018) Atlantic tropical storm in 2018

Tropical Storm Gordon was a tropical storm that caused moderate damage along the Gulf Coast of the United States in early September 2018. The seventh named storm of the 2018 Atlantic hurricane season, Gordon developed from a tropical wave that was first monitored in the Caribbean Sea on August 30. The wave moved west-northwestward toward the east coast of Florida and gradually organized. The disturbance was marked as Potential Tropical Cyclone Seven on September 2 while near the Bahamas, and early on September 3, it became Tropical Storm Gordon, moving onto the southwest coast of Florida shortly afterward. Steady intensification began after it left the coast of Florida into the Gulf of Mexico, reaching its peak intensity as a high-end tropical storm late on September 4, before it made landfall just east of Pascagoula, Mississippi, shortly afterwards. Gordon then rapidly weakened inland, before weakening into a remnant low on September 6. Gordon's remnants lingered over Arkansas for two days, and opened up into a trough on September 8. At least three deaths were attributed to the storm, and Gordon caused approximately $200–250 million in damages.


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