A Case Study of the Influence of Interactions Between Tropical Cyclones and Environment on Binary TC Tracks: Lekima and Krosa (2019)

Abstract When two tropical cyclones (TCs) simultaneously appear in close locations, they may impact with respect to each other, called binary TCs. The complex interactions exist between binary TCs and impose challenges on TC track simulation and result in significant track prediction errors. Here, we use Typhoons Lekima and Krosa (2019) as an example of a binary‐TC system to examine the influences of binary‐TC interactions on their tracks. Using the Weather Research and Forecasting model with a cloud‐resolving (3 km resolution) TC‐downscaling simulation, it is found that precisely capturing feedbacks of Krosa's fine‐scale structures to the western Pacific subtropical high (WPSH) greatly improves the accuracy of track simulations of this binary‐TC system. Conversely, due to the larger distance between Lekima and the WPSH, the asymmetric convection in Lekima only has a limited influence on the WPSH, making a negligible effect on Krosa's track. The analysis of potential vorticity tendency suggests that Krosa's asymmetric convection mainly affects the TC tracks by changing the horizontal advection (HA), while the diabatic heating makes relatively small contributions. Further analyses suggest that the asymmetric convection of Krosa weakens the strength of β ‐effect, thus diminishing its ventilation flows. This modification of ventilation flows changes the magnitude and direction of HA, consequently leading to Krosa's deceleration and zigzag motion. As Krosa's fine‐scale structures persistently interact with the environment, the western ridge of WPSH gradually gets enhanced and subsequently extends westward. This process further alters the β ‐gyres and ventilation flows of Lekima, ultimately resulting in its northwestward turning.