Abstract:Based on the ECMWF ensemble prediction system (EC-EPS) and the potential vorticity tendency (PVT) diagnosis, this paper examines the contributions of physical factors to track forecast of Typhoon Chanthu (2114) by comparing two distinct ensemble members. It is found that the typhoon centers of two ensembles both move towards the area with the largest wave number one component (WN1) of PVT. The contribution of the horizontal advection term is dominant most of the time, followed by the diabatic heating term, and the contribution of the vertical advection term is relatively small. The PVT discrepancy of the two members at bifurcation time is mainly attributed to the diabatic heating term, while that after the bifurcation time is still dominated by the horizontal advection term (i.e., steering flow). The asymmetric convective activities of two ensemble members also show different distributions at bifurcation time, which is consistent with the direction of diabatic heating, that is, the asymmetric convective structure and the vertical gradient of diabatic heating may play a key role in the movement of typhoon when the steering flow is weak, which is largely affected by the environmental factors such as water vapor, potential instability, and low-level jet. This research emphasizes the impact of diabatic heating processes (including development and asymmetric structure of convective activities) in typhoon track forecast for more accurate prediction when steering flow is weak.