Development of a MetUM (v 11.1) and NEMO (v 3.6) Coupled Operational Forecast Model for the Maritime Continent: Evaluation of Atmospheric Forecasts

The Maritime Continent (MC), located between the Pacific and Indian Oceans, is a critical region for global weather and climate systems due to its complex geography, intense precipitation, and vital role of air-sea interactions. Accurate modeling of coupled ocean-atmosphere dynamics in this region can potentially improve weather forecasts and climate projections. This study presents the development and evaluation of a fully coupled operational forecast model, integrating the UK Met Office atmospheric model (Unified Model v11.1) with the Nucleus of European Modelling of the Ocean (NEMO v3.6), at a horizontal resolution of 4.5 km, specifically tailored for the MC. The coupled model is designed to enhance atmospheric forecast accuracy by capturing air-sea interactions. Model performance was assessed using observational datasets and reanalysis products, focusing on precipitation, wind speed, and air temperature. Results show an improved forecast accuracy for the coupled model over a standalone atmospheric model. A case study on Typhoon Nakri further demonstrates an improved 10 m wind speed simulations with the coupled model, aligning more closely with reanalysis data. Air temperature forecasts, especially during nighttime and at longer lead times, also benefited from ocean-atmosphere coupling, with verification against meteorological stations confirming improved accuracy in regions with strong oceanic influence.