21 Tropical Cyclones in 2021! Why Modern TC Climatology Is Rising.

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The adjusted climatology (including 2021) for North Atlantic tropical cyclones maintains the more active 30-year values compared to the longer-term 50-year values. The number of tropical cyclones each season nowadays averages close 15 whereas the 50-year climatology is somewhat lower at 12.6 and 11.9 for 1950-2021.

Tropical StormsHurricanesMajor HurricanesACE

Index

2021217496.0
New 30-YR14.77.33.2120.5
New 50-YR12.66.42.699.2

Table 1: The 2021 seasonal activity versus new 50-year and 30-year climatology for the North Atlantic basin.

Fig. 1: The warming North Atlantic has increased the North Atlantic tropical cyclone climatology.

Fig. 2: Preliminary tracks of all tropical cyclones during the 2021 tropical cyclone season across the North Atlantic basin.

Discussion: The 2021 North Atlantic tropical cyclone season closes with seasonal totals (according to NOAA/NHC) at 21 tropical storms, 7 hurricanes and 4 intense hurricanes. The accumulated cyclone energy index was 96. The number of tropical cyclones was the 3rd highest on record trailing only 2020 (30) and 2005 (28). The number of hurricanes, intense hurricanes and ACE index was closer to normal. There were 8 U.S. land-falling tropical cyclones in 2021 after a record 12 land-falling systems in 2020. The 2-year total of 20 land-falling tropical cyclones is the most on record for a 2-year period.

The adjusted climatology (including 2021) for North Atlantic tropical cyclones maintains the more active 30-year values compared to the longer-term 50-year values. The number of tropical cyclones each season nowadays averages close 15 whereas the 50-year climatology is somewhat lower at 12.6 and 11.9 for 1950-2021. The increased number of tropical cyclones in the 30-year climatology is due to the warming North Atlantic as identified by the Atlantic multi-decadal oscillation (AMO) and tropical North Atlantic index (TNA).