Roles of interbasin frequency changes in the poleward shifts of the maximum intensity location of tropical cyclones

An observed poleward migration in the average latitude at which tropical cyclones (TCs) achieved their lifetime-maximum intensities (LMIs) was previously explained by changes in the mean meridional environments favorable to storm development linked to tropical expansion and anthropogenic warming. We show that the poleward migration is greatly influenced by basin-to-basin changes in TC frequency associated with multi-decadal variability, particularly for the Northern Hemisphere (NH). The contribution of the frequency changes to the poleward migration is comparable to that of the mean meridional environmental changes. A statistically significant global poleward trend can be identified simply from the frequency changes in each basin. An opposite trend exists in the frequency variations over the past 30 years between the North Atlantic and the eastern North Pacific where climatological mean latitudes of LMI are high (26.1 degrees N) and low (16.5 degrees N), respectively, which is the key factor in driving the frequency contribution. The strong roles of the interbasin frequency changes in the poleward migration also suggest that if the phase of multidecadal variability in the NH is reversed, as found in earlier TC records, the poleward trend could be changed to an opposite, equatorward, trend in the future.