Real-time Testing of Experimental Upgrades to the Hurricane Analysis and Forecast System, Version B (HAFSV1.1B)

The Hurricane Analysis and Forecast System (HAFS) was introduced into operations during June of 2023. Work is ongoing to improve HAFS forecasts of tropical cyclone structure, intensity, and track. Through the support of the Hurricane Forecast Improvement Project (HFIP), a real-time test was performed using an experimental version of HAFS-B (HAFSV1.1B). This experimental version contains a few upgrades designed to improve forecasts of rapid intensification as well as increase the diversity between HAFS-A and HAFS-B (with the goal of improving consensus forecasts using both versions of HAFS). One upgrade involves the use of the “prognostic closure” scale-aware closure in the Scale-Aware SAS convective scheme. Other changes include relative suppression of vertical mixing in the HYCOM ocean model (critical Richardson number), and a modification to the “tc-pbl” option in the EDMF-TKE PBL scheme to improve the prediction of outer wind radii. These experimental improvements are evaluated for the 2023 Atlantic and East Pacific hurricane seasons based on forecasts of track, intensity, and wind radii. The experimental HAFS-B forecasts are compared with an experimental HAFS-A configuration also being run in real-time, as well as the currently operational HAFS forecasts. The overall skill of all the versions are compared, as well as the correlations between the different versions, to see if the goals of improved forecast skill and increased diversity between models are being met through the upgrades. Further testing of HAFS upgrades is also discussed.