## 3 Results
### 333-m NWP Model Validation  
The 333-m NWP model provides zonal (u) and meridional (v) components of the mean wind speed at 10 m (as a diagnosed quantity) above the ground (taken as the model's surface) as well as at up to 140 vertical levels above model surface (as model prognostic quantities), separately. The gust wind speed is only estimated at 10 m above the ground. The mean and gust wind speed outputs of the NWP are compared with the station observations for the period 17 September 2020 18:00 UTC to 18 September 2020 18:00 UTC in Figures 5 and 6. NWP mean wind speeds at three vertical levels, namely 7.7 m, 10 m and 13.7 m above the surface, are compared with the 10-m anemometer measurements at each station location. At the Auckland Aero location (Figure 5a), the forecast gust wind speed values and the time of occurrence of the maximum gust speed (18 September 00:00 UTC) agrees well with those of the observation. However, the NWP model slightly underestimates the mean wind speeds. In addition, there is a difference of up to 5 m s\({}^{-1}\) between the forecast and station gust wind speed at Auckland between 18 September 6:00 UTC and 9:00 UTC. It is noteworthy that the mean speed values at 10-m and 7.7-m heights provided by the NWP model are very similar at all station locations. The strong gust wind speed on 18 September at 00:00 UTC is also accurately forecast at the Whenuapai location, while later in the day (9:00 UTC to 12:00 UTC), the model underestimates the gust values. Figure 5: Comparison of gust and mean wind speeds during 17 September 2020 18:00 UTC to 18 September 2020 18:00 UTC from the 333-m NWP model and observations, at: (**a**) Auckland Aero; (**b**) Whenuapai; (**c**) MOTAT. Regarding the mean wind speed at Whenuapai (Figure 5b), the NWP model underestimates the values after 00:00 UTC on 18 September by about 2 m s\({}^{-1}\) on average. In addition, the maximum mean wind speed was predicted at 22:30 UTC as opposed to 00:00 UTC (observation). At MOTAT (Figure 5c), the forecast mean and gust wind speeds generally agree well with the observations, the model occasionally forecasting higher gust wind speeds compared with observations. The maximum gust wind speed measured and forecast on 18 September at 00:00 UTC is the highest at the Auckland Aero station with a value close to 25 m s\({}^{-1}\), which drops to 22.5 m s\({}^{-1}\) at Whenuapai. Wind speeds at MOTAT are smaller compared with the other stations, which could be explained by the surrounding suburban terrain of MOTAT. In addition, at Auckland and Whenuapai, the modelled mean wind speed at a 13-m height agreed slightly better with the observation values. The strong wind event in Auckland on 18 September 2020 was a westerly event. Thus, it is expected that the anemometer facing NW near the top the Sky Tower is more exposed to the approaching wind and is thus able to measure the wind speeds more accurately. For more details about the Sky Tower anemometers and the sheltering effects of the tower, see [46]. Figure 6 compares the measurements of both Sky Tower anemometers with the forecasts of the NWP model. For the mean wind speeds, the NWP outputs at higher levels were used. However, the 10-m gust wind speed at the location of the Sky Tower was extrapolated to a height of 318 m using the terrain/height multipliers provided in [37]. It is evident that the NW anemometer measurements agree considerably better with the model  
Figure 6: Comparison of **(a)** gust and **(b)** mean wind speeds during 17 September 2020 18:00 UTC to 18 September 2020 18:00 UTC from the 333-m NWP model and the two anemometers mounted on the Sky Tower. data, particularly for the hours before the maximum event, i.e., 18 September at 23:00 UTC. It should be noted that the maximum wind speed at Sky Tower is recorded at 23:00, as opposed to 00:00.