Impact of CYGNSS Data Assimilation on Tropical Cyclone Forecasts in August 2017

The Cyclone Global Navigation Satellite System (CYGNSS) provides remotely-sensed surface wind observations over water and is not impeded by cloud cover or precipitation. Therefore, CYGNSS offers a unique opportunity to observe surface winds near the core of tropical cyclones. Here, we present results using two observing system experiments designed to test the impact of CYGNSS on tropical cyclone track and intensity forecasts in NOAA’s GDAS/GFS global weather modeling system. Specifically, we ran the first experiment to mimic the operational configuration (but with reduced model resolution) and the second experiment with CYGNSS data added. We ran the experiments for one month, cycling every 6 hours. The first two weeks (1-14 August) are used as spin-up with the remaining days used as the verification period (15-31 August). During the verification period, Hurricane Harvey formed in the Atlantic basin, strengthened into a Category 4 hurricane in the Gulf of Mexico, and caused widespread damage in Texas. Our assessment of CYGNSS impacts will focus on Harvey, but will also include forecast error statistics for all tropical cyclone forecasts during the period.