A Comparison between Hurricane WRF and TWRF in Typhoon Track and Rainfall Forecast over the western North Pacific

Taiwan Typhoon and Flood Research Institute (TTFRI) and Central Weather Bureau (CWB), in collaboration with NOAA Earth System Research Laboratory and Environmental Modeling Center (EMC), implemented and tested NOAA's Hurricane WRF (HWRF) system at TTFRI for typhoon forecast in a region centered on Taiwan. Two different nested-grid configurations of the HWRF model were tested in two full typhoon seasons from 2013 to 2014: one was moving nested grid for typhoon track and intensity forecast and the other was stationary nested grid for typhoon-induced precipitation forecast over Taiwan. Presented in this paper is a study in which results from the TTFRI HWRF model using these two grid configurations are evaluated in comparison with those from the Typhoon WRF (TWRF) model. The TWRF model was developed in Taiwan, consisting of the Advanced Research core of the WRF (WRF-ARW), the WRF 3DVAR system with outer loop and partial cycling, and a blending technique for model initialization using both global and regional analyses with a spatial filter. It will be first shown that the quality of typhoon track forecast of the TTFRI HWRF model using moving nested grid is much more similar to that of the EMC version of the HWRF model in the Western Pacific region from 2013 to 2014. Then, the quality of typhoon track and quantitative precipitation forecast of the TTFRI HWRF with the stationary nested-grid configuration of 45/15/5 km will be evaluated for the 2013 typhoon season against the forecast from the TWRF model. It will be shown that the TTFRI HWRF model with the static nested grid configuration has an obviously low bias for accumulated rainfall in 24 hours although the quality of track forecast is comparable with that of the TWRF model. It will also be shown that after the TTFRI HWRF mode with static nested grid was adjusted to a higher horizontal resolution of 27/9/3 km in 2014, both the qualities of the typhoon track and quantitative precipitation forecast of the TTFRI HWRF model were improved.