Impact of CyGNSS L2 Winds on Tropical Cyclone Analyses and Forecasts in the Coupled HAFS/HYCOM

For the analysis and forecasting of tropical cyclones (TCs), the main benefits of data from the CyGNSS constellation of satellites are the increased revisit frequency compared with polar-orbiting satellites and the ability to provide ocean surface wind observations through convective precipitation. Consequently, CYGNSS delivers an improved capability to observe the structure and evolution of ocean surface winds in and around tropical cyclones. This study quantifies the impact of assimilating the latest version of CYGNSS retrieved wind speed on 6-hourly analyses and 5-day forecasts of weak TCs, using a version of NOAA's Hurricane Analysis & Forecast System (HAFS) coupled with HYCOM, similar to that currently used for operational forecasting. We focus on TCs whose forecast was initialized when the TC was a tropical storm or depression. The analysis includes impacts of improved surface wind initialization on the initial ocean state and near-surface ocean evolution under the coupled TC model, as well as impacts on the skill of storm forecasts for intensity and surface wind structure.