Characteristics of rapidly intensifying tropical cyclones in the South China Sea, 1980-2016

The differences in the characteristics of the rapid intensification (RI) during the TCs that form in the SCS (referred as local TCs) and that
enter the SCS from the western North Pacific (WNP; referred as entering TCs) have not been well studied, which could contribute the inaccuracy
of current TC intensity forecast in the SCS. In this study, we used TC observations, reanalysis data and model experiments to analyze the RI
occurrences during local TCs and entering TCs in 1980e2016. We found that the significant interannual and interdecadal variations in RI
occurrences during local eastward-moving TCs were related to the strong intraseasonal oscillation (ISO) over the SCS and the WNP under La
Nina conditions. RI during local westward-moving TCs showed insignificant variations as a result of the complex interactions among the
monsoon trough, ISO and the large-scale circulation. RI during entering TCs showed strong interdecadal variations, with increased RI after
1997, even though the total number of entering TCs has decreased since 1997, which is a result of a higher number of entering TCs in the
northwestern quadrant of the WNP, a stronger ISO and weak vertical windshear over the SCS and east of the Philippines under negative phase of
Pacific Decadal Oscillation. The different variations and related mechanisms of RI indicates that distinct forecasting factors should be considered
for intensity prediction during local eastward- and westward-moving TCs and entering TCs.