Evaluation of ECMWF Ensemble Forecasts of Air-sea Fluxes against Saildrone Observations during the 2023 Atlantic Hurricane Season

Forecasting of tropical cyclones presents an unmet challenge, especially for their rapid changes in intensity. This is partially related to the unknown accuracy of air-sea energy exchanges, such as latent and sensible heat fluxes as major energy sources for tropical cyclone evolution. Forecast models struggle to resolve these processes due to sparse in-situ observations near the ocean surface. With the introduction of Saildrone uncrewed ocean surface vehicles, surface observations within tropical cyclones have been taken in real-time since 2021. During the 2023 Hurricane Season, 6 tropical cyclones were intercepted 19 times across 10 different saildrones in the Atlantic. Model validation with surface observations is crucial in improving understanding of surface processes and forecasting. In this presentation, we will be validating ocean latent and sensible heat fluxes from the European Centre for Medium-Range Weather Forecasts (ECMWF) ensemble forecast of 50 members across 11 saildrone observations in the Atlantic basin from August – October 2023. This study focuses on evaluating forecasts across lead times of up to 15 days against observation using ensemble metrics. The ensemble forecast was able to reliably predict the timing of large fluxes associated with tropical cyclones up to 10 days but not the amplitude. This analysis will help shed light on the degree to which the ensemble forecasts resolve sea-air processes and on how to improve forecasts for tropical cyclone evolution.