Abstract Typhoon Bebinca experienced an unexpected rapid intensification (RI) before landfall under dry conditions, characterized by a mid‐level relative humidity less than 50%. Throughout the RI, its inner‐core convection was highly asymmetric. Based on a high‐resolution convection‐permitting simulation, we found that the RI was initiated by an outbreak of convective precipitation in the downtilt‐left quadrant, where environmental dry air was also present during the early stage. The intrusion of mid‐level dry air enhanced evaporative cooling within stratiform precipitation, leading to the formation of a descending inflow and a stratiform‐type cold pool at mid‐to‐low levels. This descending inflow reinforced a radial convergence zone at its leading edge. Outside this convergence zone, the cold pool and the tilt‐induced vertical shear inside reached a balanced state that favored upward lifting, promoting the development of a convective band along the radially inward edge of the cold pool. This band then merged with convective cells from upstream within the convergence zone, further amplifying the inner‐core diabatic heating in the downtilt‐left region. As the vortex tilt gradually aligned with the environmental vertical wind shear, intense diabatic heating was sustained in the downshear‐left quadrant during the later RI stage, enabling Bebinca's RI under an asymmetric inner‐core convective structure. This study highlights that the interaction between vortex tilt and environmental dry air played a key role in the initiation of asymmetric inner‐core convection, implying that an accurate representation of vortex tilt may be crucial for forecasting of asymmetric RI events.
Wang et al. (Mon,) studied this question.