Multidecadal Historical Trends in Tropical Cyclone Intensity and Evolution Characteristics for Two North Atlantic Subbasins

This paper investigates the relationship between long-term trends (1980–2017) in intensity and wind evolution for tropical cyclones (TCs) within the western tropical Atlantic (WTA) and central/eastern tropical Atlantic (CETA) subbasins. Long-term TC trends in intensity, intensification time, and wind variability for the CETA were generally more significant than, and in some cases opposite to, those for the WTA. Both the TC intensity levels, as measured by the power dissipation index normalized by storm hours and proportion of rapid intensification intervals (defined as a 12-hr wind speed increase of 20 kt or more), exhibit no long-term trends in either subbasin. A TC wind variability index (WVI) calculated over 72-hr intervals of the TC lifecycle decreases for the WTA over the decades, while the CETA has the 72-hr intervals with the greatest wind speed fluctuations. The average period of intensification before the peak in TC intensity increases ~0.97 hr/year for the CETA. TC maximum intensity exhibits no trend, suggesting that TCs in the tropical North Atlantic have a trend favoring a longer intensification period to reach their lifetime maximum intensity. A correlation analysis suggests that warmer sea surface temperatures and greater moisture favor longer intensification and greater WVI. In contrast, greater 850- to 200-hPa vertical wind shear is associated with shorter intensification periods and less WVI.