An Atmosphere–Land–Ocean Coupled Global NWP System: Performance Evaluation for Potential Operational Use

Abstract This study assesses the influence of ocean–atmosphere coupling on short‐ and medium‐range forecasts of the July 2024 Indian summer monsoon using the newly configured coupled NCMRWF Unified Model (C‐NCUM). Forecasts are evaluated against the operational atmosphere–land model (NCUM) using GPM rainfall, OSTIA SSTs, and reanalysis‐derived moisture fields. The C‐NCUM system demonstrates improved simulation of monsoon rainfall and SST variability, with notable reductions in widespread wet biases over the western equatorial Indian Ocean (WEIO) and the Core Monsoon Zone. Enhanced representation of SST–convection interactions and moisture transport reduces the spurious low‐level convergence present in the uncoupled forecasts. SST diagnostics also reveal reduced warm biases and higher spatial correlation with observations, particularly over the WEIO. Forecast skill remains weaker over the eastern equatorial Indian Ocean. The results highlight the importance of dynamic air–sea coupling for advancing monsoon prediction capability.