## 3 Results
### Overview of the Event Day
Under the impact of the thunderstorm from 0600 to 1200 UTC, storm cells resulted in short-duration intense rainfall in many areas and caused a decrease in atmospheric visibility. The 6-hr accumulated precipitation during 0600-1200 UTC at Cengwen (Figure 5b), Yuemei (Figure 5c), and Yanpu (Figure 5d) was 55, 77.5, and 43 mm,  
Figure 5: Observed hourly visibility (km; blue line) and accumulated precipitation (mm; red bar) at (**a**) Pingtung meteorological station, and observed hourly surface pressure (hPa; blue line) and accumulated precipitation (mm; red bar) at the (**b**) Cengwen, (**c**) Yuemei and (**d**) Yanpu AWSs from 0400 to 1500 UTC (1200 to 2300 LST) on 5 August 2018.  
respectively, and the 1-hr maximum precipitation occurred at 1600 UTC for the three stations. The precipitation measured at the Cengwen, Yuemei, and Yanpu station fit the requirements of a short-duration intense rainfall event as the rainfall exceeded 30 mm during a 12-h period ([PERSON] et al., 2017). The Pingtung meteorological station recorded precipitation of less than 30 mm in six hours. However, the horizontal visibility of Pingtung Airport less than 5 km reached the condition of prohibiting pilots to fly. The reduced horizontal visibility at Pingtung Airport might have been due to strong rainfall around the area (Figure 4f). As the thunderstorm approached, the surface pressure continued to drop greatly for the Cengwen (Figure 5b), Yuemei (Figure 5c), and Yanpu (Figure 5d) stations until the front passed completely. The lowest surface pressures measured by the three stations were 989.2, 990.7, and 998.6 hPa at the Cengwen (Figure 5b), Yuemei (Figure 5c), and Yanpu (Figure 5d) stations, respectively, during the afternoon from 0500 to 0700 UTC. The observed, DA01 assimilated, NDA01 non-assimilated hourly surface pressure, temperature and dew-point temperature of Pingtung Airport from 0100 to 0900 UTC (0900 to 1700 LST) on 5 August 2018 are shown in Figure 6. The changes of surface pressure (Figure 6a), temperature (Figure 6b) and dew-point temperature (Figure 6c) were quite similar in observations, simulations with data assimilation and without data assimilation. Although the rainfall time was 1600 LST at Pingtung (Figure 5a), surface pressure (Figure 6a) and temperature (Figure 6b) dropped rapidly from 0400 to 0600 UTC (1200 LST to 1400 LST), due to the sea breeze effect associated with cool moist air. Then the dew-point temperature (Figure 6c) increased to promote cloud development and block solar radiation. Compared with DA01 assimilated simulations, the changes of surface pressure (Figure 6a) and temperature (Figure 6b) of NDA01 non-assimilated simulations during 0100-0700 UTC were closer to those of observations, which were caused by stronger sea breeze in DA01 than in NDA01 simulations and will be examined in Figures 8-10. However, further examination of the time period during 0500-1000 UTC in DA01 and NDA01 simulations revealed that the surface pressure (Figure 7a) and temperature (Figure 7c) of DA01 assimilated simulations after 0700 UTC were closer to those of observations than those of NDA01 non-assimilated simulations, which were caused by the effect of more accurate precipitation in DA01 than in NDA01 simulations. More accurate rainfall forecast in the model simulations tends to have variables such as atmospheric pressure and temperature closer to observations. The DA02 simulations performed better in rainfall forecast than the DA01 and DA03 simulations, and will be further examined in the following sections. Compared with the DA01 (Figure 7a,c) and NDA02 (Figure 7b,d) simulations, the changes of surface pressure (Figure 7b) and temperature (Figure 7d) in the DA02 simulations had a closer distribution to those of observations. Figure 6: The observed (solid lines), DA01 assimilated (dot lines) and NDA01 non-assimilated (dashed lines) hourly surface (**a**) pressure, (**b**) temperature, (**c**) dew-point temperature of Pingtung Airport from 0100 to 0900 UTC (0900 to 1700 LST) on 5 August 2018.