A post-tropical cyclone is a former tropical cyclone.
Two classes of post-tropical cyclones exist:
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.A few examples falling into this grey area are listed below.
However, there has been an occasion that the United States National Hurricane Center went against that definition and designated Calvin (2011) as a 35-knot remnant low.
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)".
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.
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.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.
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.
The terminology was initiated by 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 on May 15, 2010.
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.
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.
A subtropical cyclone is a weather system that has some characteristics of a tropical and an extratropical cyclone.
Hurricane Vince was an unusual hurricane that developed in the northeastern Atlantic basin. Forming in October during the 2005 Atlantic hurricane season, it strengthened over waters thought to be too cold for tropical development. Vince was the twentieth named tropical cyclone and twelfth hurricane of the extremely active season.
Hurricane Charley was the first hurricane to threaten the East Coast of the United States since Hurricane Gloria the previous year. The third tropical storm and second hurricane of the season, Charley formed as a subtropical low on August 13 along the Florida panhandle. After moving off the coast of South Carolina, the system transitioned into a tropical cyclone and intensified into a tropical storm on August 15. Charley later attained hurricane status before moving across eastern North Carolina. It gradually weakened over the north Atlantic Ocean before transitioning into an extratropical cyclone on August 20. Charley's remnants remained identifiable for over a week until after crossing the British Isles and dissipating on August 30.
Tropical Storm Zeta was a very late-developing tropical storm over the central Atlantic that formed after the 2005 Atlantic hurricane season and continued into January 2006. Becoming a tropical depression at approximately midnight on December 30 (UTC), it became the record-breaking thirtieth tropical cyclone of the 2005 Atlantic hurricane season and after intensifying into Tropical Storm Zeta six hours later, it became the season's twenty-seventh named storm. Zeta was one of only two Atlantic tropical cyclones to span two calendar years.
Subtropical Storm Nicole was the first subtropical storm to receive a name using the standard hurricane name list that did not become a tropical cyclone. The fifteenth tropical or subtropical cyclone and fourteenth named storm of the 2004 Atlantic hurricane season, Nicole developed on October 10 near Bermuda from a broad surface low that developed as a result of the interaction between an upper level trough and a decaying cold front. The storm turned to the northeast, passing close to Bermuda as it intensified to reach peak winds of 50 mph on October 11. Deep convection developed near the center of the system as it attempted to become a fully tropical cyclone. However, it failed to do so and was absorbed by an extratropical cyclone late on October 11.
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.
The 2005 Azores subtropical storm was the 19th nameable storm and only subtropical storm of the record-breaking 2005 Atlantic hurricane season. It was not officially named by the US National Hurricane Center as it was operationally classified as a non-tropical low. The storm developed in the eastern Atlantic Ocean out of a low-pressure area that gained subtropical characteristics on October 4. The storm was short-lived, crossing over the Azores later on October 4 before becoming extratropical again on October 5. Neither damages nor fatalities were reported during that time. After being absorbed into a cold front, the system went on to become Hurricane Vince, which affected the Iberian Peninsula.
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.
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.
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 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.
Hurricane Arlene was a long-lived tropical cyclone that moved eastward in an erratic fashion in the northern Atlantic Ocean in mid-August 1987. The first named storm of the 1987 Atlantic hurricane season, Arlene formed out of an area of low pressure associated with a decaying frontal system along the North Carolina coastline, Arlene tracked in a general eastward direction across the Atlantic Ocean, taking an erratic track with several curves. On August 13, the storm brushed Bermuda as a weak tropical storm before continuing out to sea. On August 20, the storm briefly stalled before becoming a hurricane two days later. Early on August 24, the storm transitioned into an extratropical cyclone over the far north Atlantic before curving southeast and dissipating near the Iberian Peninsula on August 26.
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, and the storm's remnants merged with a separate system near the British Isles on October 7.
The 2013 Atlantic hurricane season was a well below average Atlantic hurricane season and the first since 1994 with no major hurricanes. It was a well below average season for both hurricanes and major hurricanes but it was a slightly above average season for named storms. 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 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.
The following is a glossary of tropical cyclone terms.
The 2019 Atlantic hurricane season was the fourth consecutive year of above-average and damaging seasons dating back to 2016. It is tied with 1969 as the fourth-most active Atlantic hurricane season on record in terms of named storms, with 18 named storms and 20 tropical cyclones in total, although many were weak and short-lived, especially towards the end of the season. The season officially began on June 1 and ended on November 30. These dates historically describe the period each year when most tropical cyclones form in the Atlantic basin and are adopted by convention. However, tropical cyclogenesis is possible at any time of the year, as demonstrated by the formation of Subtropical Storm Andrea on May 20, marking the record fifth year in a row where a tropical or subtropical cyclone developed before the official start of the season, breaking the previous record of four consecutive years set in 1951–1954. For a second year in a row, no tropical cyclones formed during the month of June.
The 2018 Pacific hurricane season produced the highest accumulated cyclone energy value on record in the basin. With 23 named storms, it was the fourth-most active season on record, tied with 1982. The season also featured seven landfalls, six of which occurred in Mexico. 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. However, tropical cyclone formation is possible at any time of the year, as illustrated when the first tropical depression formed on May 10, five days prior to the official start of the season.
Hurricane Humberto was a large and powerful tropical cyclone that was the first storm to produce hurricane-force winds on the island of Bermuda since Nicole in 2016. The eighth named storm, third hurricane, and second major hurricane of the 2019 Atlantic hurricane season, Humberto developed from a disturbance in the Atlantic on September 13. The disturbance slowly organized as it moved through the Southern Bahamas, and late on September 12th, it was designated Potential Tropical Cyclone Nine, as it posed a threat to imminent land areas in Florida and the Bahamas. The next day, the potential cyclone developed a closed surface circulation and was designated a tropical depression. The depression strengthened into Tropical Storm Humberto a few hours later. After re-curving northeastward, away from the United States, Humberto began to intensify. Humberto reached hurricane strength at 3:00 UTC September 16th, and peaked as a Category 3 hurricane as it approached Bermuda. The eastern portion of Humberto's eye moved over Bermuda as it began to evolve into an extratropical cyclone, a process it completed by early on September 20. Humberto accelerated east and gradually weakened before it was absorbed by a larger storm over the British Isles.