An Ensemble Approach to Investigate Typhoon Hagupit (2020) Rainfall Distribution

Ting-Yu Cha

Extreme rainfall from tropical cyclones (TCs) is one of the main hazards and affects people around the world. TC rainfall accumulation is driven by the track and motion which determine the synoptic-scale location and duration of rainfall to first order. However, mesoscale interactions between the PV field, shear, large-scale integrated water vapor transport, and terrain can produce extreme precipitation well away from the center. To investigate how precipitation intensity, duration and distribution influenced by TC, low-level monsoonal flow, and mesoscale fields interactions, this study employed a 40-member ensemble generated from the PSU EnKF WRF model. EnKF ensemble forecasts for Typhoon Hagupit (2020) were evaluted when Hagupit tracked to the north of Taiwan, resulting in over 300 mm in 24 hours. The underlying mechanisms between two subsets of members that predicted good and worst precipitation forecasts are compared, using the 24-hour EnKF forecasts for Hagupit to characterize the variabilities in the QPF skill with the equitable threat score (ETS) and spatial correlation coefficient (SCC). The differences between these two subsets will be examined and presented in the class.