Eastward Shift of Northwest Pacific Tropical Cyclone Genesis Frequency Anomaly in Decaying El Nino

This study focuses on longitudinal evolution of tropical cyclone genesis frequency (TCGF) anomaly over the western North Pacific (WNP) from July to October in the El Nino decaying (EDC) years and its possible mechanisms. Results show that TCGF anomaly exhibits a dipole pattern with a negative center in the eastern WNP and a positive center in the western WNP. In particular, the mean position of negative (positive) anomaly shifts eastward from 130 degrees E (120 degrees E) in July to 160 degrees E (145 degrees E) in October. Moreover, the evolving feature of negative TCGF anomaly is exhibited more clearly. This evolution of TCGF anomaly largely determines the distribution of climatological TC kinetic energy anomaly, which also shifts eastward and persists throughout the EDC fall. Tropical Indian Ocean warming and equatorial central eastern Pacific cooling jointly modulates the large-scale atmospheric circulation and environmental conditions over the WNP, contributing to the eastward shift of TCGF anomaly during the EDC summer and fall. A better understanding of the evolution of TCGF anomaly could be beneficial for the improvement of the seasonal TC prediction over the individual regions over the WNP for the EDC years.