Tropical cyclone genesis involves multiscale interactions among large-scale tropical wave activity, mesoscale convective organization, low-level vortex development, and oceanic heat and moisture supply. This study examines the pre-genesis stage of Super Typhoon Ragasa (2025) over the western North Pacific using ERA5 reanalysis and GPM IMERG precipitation data. In a storm-relative framework, we diagnose the phase relationships among wave-related wind anomalies, moist static energy (MSE) budget terms, precipitation, vertical moistening, and low-level vorticity, and further discuss the air–sea heat and moisture coupling characteristics during the later stage of disturbance organization based on surface heat flux-related variables.

The results show that equatorial-wave-related circulation anomalies organized a coherent thermodynamic phase structure around the moving disturbance. Positive MSE tendency and wave–background MSE transport were mainly located from the leading to near-center phases, while precipitation, anomalous ascent, and low-level vortical response were more pronounced from the center to rear phases. Vertical diagnostics indicate that lower- to mid-tropospheric moistening and anomalous ascent were concentrated in the center-to-rear phases, reflecting a transition from wave-organized MSE recharge to convective–vortical coupling. Air–sea flux diagnostics further show that, during the later stage of disturbance organization, the warm sea surface background and evolving near-surface winds provided sustained heat and moisture input for maintaining boundary-layer MSE.

Overall, Ragasa’s pre-genesis evolution illustrates a multiscale pathway in which equatorial waves first reorganized the thermodynamic and moisture structure of the tropical disturbance, while subsequent convective organization and enhanced air–sea heat and moisture coupling supported the continued growth of the incipient vortex. This case provides a process-based perspective for further quantifying how atmospheric wave dynamics regulate the timing and efficiency of oceanic heat and moisture supply during tropical cyclone embryo development.