A post-tropical cyclone is a former

tropical cyclone 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 and squalls. Depend ...

that no longer possesses enough tropical qualities to be considered a tropical cyclone. The word may refer to a former tropical cyclone undergoing extratropical transition or a tropical cyclone degenerating into a remnant low. A tropical cyclone degenerating into a

trough Trough may refer to: In science * Trough (geology), a long depression less steep than a trench * Trough (meteorology), an elongated region of low atmospheric pressure * Trough (physics), the lowest point on a wave * Trough level (medicine), the l ...

or wave, or having it's low level circulation dissipate overland, lacks a cyclonic circulation and is referred as remnants instead of a post-tropical cyclone. However, post-tropical cyclones or remnants can continue producing high winds and heavy rains. Paulette 2020-09-16 1420Z

Classification

Classes

Two classes of post-tropical cyclones exist *

Extratropical 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 ...

, which is

frontal Front may refer to: Arts, entertainment, and media Films * ''The Front'' (1943 film), a 1943 Soviet drama film * ''The Front'', 1976 film Music * The Front (band), an American rock band signed to Columbia Records and active in the 1980s and e ...

, sometimes still retains winds of

hurricane 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 and squalls. Depend ...

tropical storm 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 and squalls. Depend ...

force.

Hurricane Paulette Hurricane Paulette was a strong and long-lived Category 2 Atlantic hurricane which became the first to make landfall in Bermuda since Hurricane Gonzalo did so in 2014. The sixteenth named storm and sixth hurricane of the record-breaking 2020 ...

(2020) provides a recent example of an extratropical cyclone, in which it no longer has a warm core in higher latitudes when it was over

Nova Scotia Nova Scotia ( ; ; ) is one of the thirteen provinces and territories of Canada. It is one of the three Maritime provinces and one of the four Atlantic provinces. Nova Scotia is Latin for "New Scotland". Most of the population are native Eng ...

and all points north in its trajectory. * Remnant low, which is non-frontal, has maximum sustained winds of less than 34 knots, and mainly consists of stable

stratocumulus A stratocumulus cloud, occasionally called a cumulostratus, belongs to a genus-type of clouds characterized by large dark, rounded masses, usually in groups, lines, or waves, the individual elements being larger than those in altocumulus, and th ...

with little to no convective activity. These shallow systems may meander for some time before opening into a trough of low pressure, or by being absorbed into an extratropical cyclone.

Formation

A post-tropical cyclone is formed when the typical characteristics of a

are replaced with those of

extratropical 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 ...

s, otherwise known as

. After the initial formation, a post-tropical cyclone has the potential to gain strength and intensity by forming an extratropical storm. If a post-tropical cyclone does become an extratropical storm, it will eventually decay through the process of

occlusion Occlusion may refer to: Health and fitness * Occlusion (dentistry), the manner in which the upper and lower teeth come together when the mouth is closed * Occlusion miliaria, a skin condition * Occlusive dressing, an air- and water-tight trauma ...

Impacts

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 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 and squalls. Depend ...

Origin

The terminology was initiated by

Canadian Hurricane Centre The Canadian Hurricane Centre (CHC; french: Centre canadien de prévision des ouragans) is an organisation that monitors and warns of the threat of tropical cyclones such as hurricanes and tropical storms. CHC is a division of the Meteorological Se ...

in 1998 during

Tropical Storm Bonnie The name Bonnie has been used for ten tropical cyclones worldwide, eight in the Atlantic Ocean (one of which crossed over into the eastern Pacific Ocean) and one each in the Western Pacific and the Australian region of the Southern Hemisphere. In t ...

. 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. The term was later adopted by the

National Weather Service The National Weather Service (NWS) is an Government agency, agency of the Federal government of the United States, United States federal government that is tasked with providing weather forecasts, warnings of hazardous weather, and other weathe ...

on May 15, 2010.

Synonym

The

Bureau of Meteorology The Bureau of Meteorology (BOM or BoM) is an executive agency of the Australian Government responsible for providing weather services to Australia and surrounding areas. It was established in 1906 under the Meteorology Act, and brought together ...

Australia Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, sma ...

refers to a former tropical cyclone as an "ex-tropical cyclone".http://www.bom.gov.au/nt/forecasts/tcoutlook.shtml An example is ex-tropical cyclone Oswald.

References

{{Extratropical cyclones Meteorological phenomena *

Post Post or POST commonly refers to: *Mail, the postal system, especially in Commonwealth of Nations countries **An Post, the Irish national postal service **Canada Post, Canadian postal service **Deutsche Post, German postal service **Iraqi Post, Ira ...

Types of cyclone Vortices Weather hazards