Numerical Simulation of Rapid Tropical Disturbance Development: Sensitivity to Topography and Convection Triggering

The initiation and subsequent intensification of tropical disturbances (TDs) remain challenging for numerical weather prediction. This study examines a systematic over-intensification tendency in the Korean Integrated Model (KIM) for a June 2025 case near the Mariana Islands and explores plausible mechanical and thermodynamic contributors. Using high-resolution (8 km) WRF simulations, we find evidence that the tendency is linked to an interaction between island-induced low-level convergence and the energy-based initiation logic of the operational KSAS convection scheme. In this case, topography appears to provide an important physical trigger for TD initiation by modifying low-level flow and enhancing convergence. While topography is closely associated with initiation, the convection scheme influences subsequent vertical development and the resulting intensity. Specifically, the operational KSAS-KIM configuration tends to respond early to lower-tropospheric energy maxima, which can favor rapid growth. In contrast, applying the NTDK (New Triggering Design for KIM; KSAS-EXP) approach—which uses buoyancy and condensate thresholds—reduces unrealistic intensification by limiting deep convection to more physically plausible conditions. These results suggest that as global models move toward finer resolutions, carefully balancing topographic forcing and convection-initiation mechanisms may help improve forecast realism.