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

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 3^rd 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).