Influence of Track Change on the Inconsistent Poleward Migration of Typhoon Activity

Tropical cyclone (TC) lifetime maximum intensity (LMI) positions have been reported to migrate poleward globally during the last several decades. However, during the TC peak season, the trend of TC LMI position over the western North Pacific (WNP) is not as robust as that of genesis position. In this study, we found that the TC track change plays important roles in decreasing the genesis-to-LMI latitude distance (G2LD), which therefore leads to the inconsistent long-term trends of genesis and LMI positions. A statistical approach was applied to quantitatively estimate the contributions by TC track change to the G2LD trend. The results show that the increase of near-land formed short-track TCs and the decrease of northwestward moving and eastward posited recurving TCs combined to make the largest contribution to the decreasing trend of the G2LD and thus to the insignificant long-term trend of LMI position during peak season. Such TC track changes are closely related to the La Nina-like warming pattern over the Pacific. The northeastward retreatment of the western Pacific subtropical high also plays an important role in reducing the northwestward moving TCs and increasing the recurving TCs over the northwestern WNP. Applying the same statistical approach to TC genesis positions indicates that the decrease of low-latitude formed TCs makes the largest contribution to the poleward migration of genesis position, and the increase of high-latitude formed TCs takes the second place. These low-latitude formed TCs are mainly featured by northwestward moving and recurving tracks.