A post-tropical cyclone is a former

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 ...

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 its 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/Other post-tropical cyclones

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 p ...

, which is frontal, sometimes still retains winds of

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 ...

tropical storm 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 lo ...

force. Hurricane Paulette (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 a Provinces and territories of Canada, province of Canada, located on its east coast. It is one of the three Maritime Canada, Maritime provinces and Population of Canada by province and territory, most populous province in Atlan ...

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 the ...

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 p ...

s, otherwise known as extratropical transition. 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.

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 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 ...

Origin

The terminology was initiated by Meteorologist Peter Bowyer of the Canadian Hurricane Centre in 1998 during Tropical Storm Bonnie. 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 Government of Australia, Australian Government that is responsible for providing Weather forecasting, weather forecasts and Meteorology, meteorological services to Australia a ...

Australia Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...

refers to a former tropical cyclone as an "ex-tropical cyclone". An example is ex-tropical cyclone Oswald.

References

{{Cyclones Meteorological phenomena * Post Types of cyclone Vortices Weather hazards