Potential impacts of radio occultation data assimilation on forecast skill of tropical cyclone formation in the Western North Pacific

This study assesses the potential influence of global navigation satellite system (GNSS) radio occultation (RO) data assimilation on the forecast skill of tropical cyclone formation over the western North Pacific in September-October 2019 through a regional model. Data from the Constellation Observing System for Meteorology, Ionosphere, and Climate mission II are applied. The forecast skill considers the hits and misses for nine developing cases and the false alarms and correct negatives for 23 non-developing cases. Forecasts assimilating GNSS RO data reduce the false alarm ratio by 20% and increase the accuracy rate by 19%, compared to forecasts without GNSS RO data. Assimilation of GNSS RO data increases mid-level moisture around the disturbance centers at the initial time of the forecasts. It also increases low-level vorticity for developing cases but decreases vorticity throughout most of the troposphere for non-developing cases. These lead to improved forecast performance for tropical cyclone formation.