## 4 Results for Saola
The times for exceedance are, in general, around or before the actual occurrence, as shown in Figure 8. A similar conclusion can also be drawn for the gust prediction, as shown in Figure 9.  
Table 4 shows the comparison of the time at which the anemometers reach their maximum values between the observations and simulations. For the observations, the times for the maximum wind speeds are generally around 22H, apart from CB5. For CB5, fluctuations are recorded at around 19H, leading to an earlier time for the maximum winds, but a local maximum is also attained at around 22H. The times for the RAMS simulation to reach the maximum values are around 20H for all anemometers. For the PALM simulation, it gives maximum winds at around 20H for CB5 and CB6, similar to that of the RAMS. Its times for the maximum winds are around 21H for the other anemometers. In general, the maximum values have a time difference of around 1-2 h between the observations and numerical simulations, and the difference is even larger in the model run initialized at 00 UTC. This time discrepancy is related to the inadequate NCEP model prediction of Saola's track and wind structure, even with a forecast lead time of around 12 h only. It is reflected in the wind direction at CB5 when comparing the actual and the simulated values. The comparison is shown in Figure 10. The measured and simulated wind direction of CB5 \begin{table}
\begin{tabular}{l c c c c c c} \hline
**Wind Speed (m/s)** & **CB1** & **CB3** & **CB5** & **CB6** & **CB7** & **CB8** \\ \hline measurement & 14.9 & 16.7 & 26.3 & 21.9 & 16.3 & 12.6 \\ \hline RAMS & 17.4 & 17.2 & 19.6 & 19.6 & 17.4 & 17.4 \\ \hline \% diff of RAMS & 17\% & 3\% & \(-\)26\% & \(-\)11\% & 7\% & 38\% \\ \hline PALM & 17.5 & 16.3 & 23.7 & 24.4 & 20.0 & 18.2 \\ \hline \% diff of PALM & 18\% & \(-\)3\% & \(-\)10\% & 11\% & 23\% & 44\% \\ \hline \end{tabular}
\end{table} 
Table 2: Average of 10 min mean wind speed and percentage error with respect to the measurement for Saola. \begin{table}
\begin{tabular}{l c c c c c c} \hline
**Wind Speed (m/s)** & **CB1** & **CB3** & **CB5** & **CB6** & **CB7** & **CB8** \\ \hline measurement & 30 & 29.1 & 44.9 & 41.7 & 31.2 & 21.7 \\ \hline RAMS & 29.9 & 30.2 & 34.7 & 34.5 & 31.0 & 30.9 \\ \hline \% diff of RAMS & 0\% & 4\% & \(-\)23\% & \(-\)17\% & \(-\)1\% & 42\% \\ \hline PALM & 28.4 & 34.0 & 38.9 & 38.8 & 31.4 & 27.3 \\ \hline \% diff of PALM & \(-\)5\% & 17\% & \(-\)13\% & \(-\)7\% & 1\% & 26\% \\ \hline \end{tabular}
\end{table} 
Table 3: Maximum of 10 min mean wind speed and percentage error with respect to the measurement for Saola. are both generally northerly to begin with. However, the PALM exhibits a sharp change in wind direction to easterly at around 21:30H, while the actual measurement shows a much more gradual shift from generally northerly at around 20H to easterly winds at around 23H. Comparing this to the time series of the wind speeds in Figure 8, both the measured and simulated wind speeds show a generally decreasing trend after the wind direction veers to the east, which could be attributed to the local terrain effect due to the higher topography along the two sides of the bridge. As an illustration of the simulated wind field for the PALM, the wind distribution at a height of about 70 m above the mean sea level is shown in Figure 11a. It can be seen that the PALM manages to illustrate the fine details of the wind pattern, e.g., the lower wind speed and even the reverse flow by a small hill near the northern boundary of the simulation domain. A vertical cross-section of the wind is obtained across the bridge. The location of the cross-section is shown in Figure 2a. An example of the cross-section is shown in Figure 11b. Due to the blockage of the bridge deck and the arc, the wind speeds are lower downstream of these super-structures of the bridge. On the other hand, the wind speeds are much higher if there are no physical blockages.