The HAFSv1.1A Real-Time Parallel Experiment with Upgraded Model Resolution, Initialization, Physics and MOM6 Ocean Coupling

Hurricane Analysis and Forecast System version 1 (HAFSv1) with two configurations (HAFSv1A and HAFSv1B) was implemented as NCEP’s operational regional hurricane forecast system in June, 2023. To further improve hurricane forecast skills and prepare for the next HAFS upgrade, an experimental HAFSv1.1A configuration was developed based on the operational HAFSv1A, and was selected as one of the Hurricane Forecast Improvement Program (HFIP) real-time parallel demo projects for the 2023 hurricane season. The HAFSv1.1A experiment features a higher resolution (5.4 vs. 6 km) regional parent domain with a 1.8-km (vs. 2-km) resolution storm-following moving nest, an upgraded vortex initialization technique which is able to relocate and cycle cloud (hydrometeor) variables, together with improved inner-core data assimilation by assimilating additional high-resolution GOES-R meso floater AMVs. In addition to these upgrades to the latest HAFS system, Thompson microphysics scheme (instead of the GFDL microphysics scheme) and the newly developed regional MOM6 (instead of HYCOM) ocean coupling are utilized in HAFSv1.1A. Retrospective tests were conducted for the 2021-2022 North Atlantic basin storms, which demonstrated that the HAFSv1.1A experiment produced near neutral storm track forecast skill compared to operational HAFSv1A, while obtaining 5-10% improvement in intensity forecast skill for almost all forecast lead times. Results from the HAFSv1.1A real-time parallel experiment for the 2023 hurricane season will be analyzed, focusing on diagnostics, assessment and comparisons with the operational regional hurricane forecast systems and other HFIP real-time parallel experiments.