A Vorticity-Based Indicator for Typhoon Intensity Forecasting

Accurate tropical cyclone (TC) intensity forecasting remains challenged due to the lack of high-spatiotemporal-resolution observations of inner-core dynamics. This study introduces a novel structural indicator, Area-Mean Vorticity (VORm), derived from minute-scale FY-4B atmospheric motion vectors using the SPA-FABI framework. We identify a distinct "U-shaped" lifecycle in vorticity variability, identifying anomalous high-frequency fluctuations as robust precursors for TC rapid intensity change. Integrating VORm into linear (MLR, R²=0.97, RMSE=5.239 kt) and non-linear (XGBoost, RMSE=5.778 kt) models significantly enhances 6-hour forecast skill, with VORm ranking as a top-tier indicator alongside other well-known dynamical and thermodynamic environmental drivers. In physical terms, a critical synergy is established: environmental factors such as sea surface temperature (SST) define the theoretical ceiling of potential intensity, while VORm quantifies the efficiency of the TC inner-core engine in realizing this potential. Furthermore, SHAP (Shapley Additive Explanation) analysis also reveals that VORm serves as a low-variance "anchor" signal, stabilizing predictions against environmental uncertainty. Operationally, VORm fills the critical gap for real-time, high-fidelity structural predictors, offering a novel and effective pathway to reduce short-term TC intensity forecast errors.