Post-tropical Cyclone - Wikipedia

Classes

Two classes of post-tropical cyclones exist

• Extratropical cyclone, which is frontal, sometimes still retains winds of hurricane or tropical storm force.[1] Hurricane Paulette (2020) provides a recent example of an extratropical cyclone,[3] in which it no longer has a warm core in higher latitudes when it was over Nova Scotia and all points north in its trajectory.[4]
• Remnant low, which is non-frontal, has maximum sustained winds of less than 34 knots, and mainly consists of stable stratocumulus 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.[1][5][6]

Other post-tropical cyclones

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.[7] A few examples falling into this grey area are listed below.

• Eugene (2011)[8]
• Michael (2012)[9]
• Nadine (2012)[10]
• Humberto (2013)[11]
• Joaquin (2015)[12]
• Matthew (2016)[13]
• Jerry (2019)[14]
• Paulette (2020)[15]
• Guambe (2021)
• Linda (2021)[16]
• Batsirai (2022)
• Emnati (2022)
• Blas (2022)[17]
• Frank (2022)[18]
• Howard (2022)[19]
• Kay (2022)[20]

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.[21] 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.[22]