Recent global increase in multiple rapid intensification of tropical cyclones.

The rapid intensification (RI ≥ 30 knots/24-h) of tropical cyclones (TCs) makes TC forecasting difficult, resulting in severe damage to property and life. Forecasting can get even worse if TCs have experienced RI more than once (referred to as "multiple-RI TCs") in their lifetime. On a global scale, the relation between long-term trends of multiple-RI TC frequency and maximum potential intensity (MPI) changes is investigated in this study. During 1981-2020, the frequency of multiple-RI TCs significantly increased at a rate of 1.2 TCs/decade, which was primarily due to the upper phases of TC becoming conducive to RI as MPI increased. Our analysis shows that the frequency of multiple-RI TCs has increased by 82.43% in 2000-2020 compared to that in 1981-2000, whereas the frequency of single RI TCs has increased by only 1.63%. The rise in MPI elevates the initial intensity at which a TC undergoes maximum intensification rate, making post-Tropical Storm stages of TCs conducive to RI. As a result, TCs can undergo RI multiple times even following a weakening before the intensity approaches MPI.