Dynamic forcing behind Hurricane Lidia's rapid intensification

Abstract. This study examines Hurricane Lidia's rapid intensification (RI) in the understudied northeastern Pacific, focusing on its interaction with an upper-level trough. Using IFS-ECMWF ensemble forecasts and ERA5 reanalysis, we analyze the large-scale dynamical mechanisms driving Lidia's intensification. Results show that the trough played a crucial role in promoting RI by enhancing synoptic-scale ascent, upper-level divergence, and eddy flux convergence. In the higher-intensification ensemble group, a coherent sequence emerged in which enhanced negative Trenberth forcing appeared several hours before RI onset, followed by marked increases in upper-level divergence, cyclonic vorticity advection, and mid-tropospheric moistening. These signals collectively reduced vertical wind shear over the storm and strengthened the upper-level outflow, creating an environment highly conducive to RI. In contrast, the lower-intensification group exhibited weaker forcing, higher shear, and a lack of sustained divergence in upper levels. These findings highlight the importance of diagnosing early dynamical triggers for RI, particularly in regions where operational access to high-resolution models is limited. A conceptual schematic synthesizes these multi-stage processes, highlighting how upper-level dynamical forcing and favorable thermodynamic conditions acted jointly to precondition and then accelerate RI. This approach provides a cost-effective framework for anticipating RI using ensemble-based diagnostics and could serve as a valuable forecasting tool in data-sparse areas such as the Pacific coast of Mexico. Future studies should combine this large-scale methodology with high-resolution simulations to better capture storm-scale processes and validate multi-scale interactions in RI events.