# Tropical Cyclone Winds from WindSat, AMSR2, and SMAP: Comparison with the HWRF Model
## Methods
### Time Interpolation  
In this section, we address the temporal mismatch between HWRF and the satellite observations. In order to facilitate a more direct comparison between the satellites and the models, the spatially resampled HWRF wind fields from the model times surrounding each satellite pass were interpolated to the time of the satellite wind field. The resulting time-interpolated 2D HWRF wind fields could be compared to the satellite observations. However, this simple time interpolation may not properly account for the movement of the storm in space and time, which in some cases could result in spurious and unrealistic features in the time-interpolated fields. An example of this is provided in Figure 7, which shows the resampled HWRF wind field that has been interpolated to the time of a SMAP overpass over Typhoon Mangkhut on 15 September 2018 at 22:34 UTC. An un-physical double-eye feature is clearly seen in the time-interpolated HWRF wind field. Spurious features like this can emerge when the wind field of well-organized and/or rapidly changing/moving storms is interpolated between two 6-h scenes. Care must be taken when comparing satellite and HWRF winds in these instances. In order to address these types of cases, an intermediate step can be taken between resampling of the high-resolution data and performing the temporal interpolation. This \begin{table}
\begin{tabular}{c c c} \hline
**Storm** & **Basin** & **Dates** \\ \hline Trami & Pacific & 23 September 2018–24 September 2018 \\ Michael & Atlantic & 7 October 2018–12 October 2018 \\ Yutu & Pacific & 23 October 2018; 26 October 2018–27 October 2018 \\ Idai & Southern Hemisphere & 9 March 2019–10 March 2019; 12 March 2019–14 \\ March 2019 & Adrian & 25 August 2019–7 September 2019 \\ Dorian & Atlantic & 26 September 2019–27 September 2019; 29 September 2019–1 October 2019; 9 October 2019 \\ Lorenzo & Atlantic & 2019–1 October 2019; 9 October 2019 \\ Hagibis & Pacific & 6 October 2019–13 October 2019 \\ Laura & Atlantic & 21 August 2020–27 August 2020 \\ Haishen & Pacific & 1 September 2020–7 September 2020 \\ Paulette & Atlantic & 7 September 2020–23 September 2020 \\ Teddy & Atlantic & 14 September 2020–23 September 2020 \\ \hline \end{tabular}
\end{table} 
Table 1: \(Cont.\)  
Figure 7: The resampled HWRF wind field that has been interpolated (**a**) to the time of the SMAP pass (22:34 UTC) (**b**) over Typhoon Mangkhut on 15 September 2018. An un-physical double-eye feature is clearly visible in the resampled HWRF field. involves spatially shifting the two resampled wind fields surrounding a given satellite pass so that their storm centers align with the storm center as seen by the satellite; i.e., shifting the model winds into a storm-centric coordinate system [26; 27]. To perform this shifting, the storm center as seen by the satellite was first visually determined from a plot of the observed wind field with the aid of the Best Track data of the National Hurricane Center (NHC) [28]. Next, the storm centers from the resampled HWRF fields surrounding the satellite pass were visually determined as well. Once this was done, both resampled 2D HWRF wind fields were fully shifted so that the HWRF storm centers aligned with the satellite storm center. This process is illustrated in Figure 8 for the case of the SMAP pass over Typhoon Mangkhut on 15 September 2018. The top two panels show the resampled HWRF winds surrounding the SMAP pass before shifting, and the bottom two panels show the same resampled HWRF winds shifted to the SMAP center. The satellite center and the original HWRF centers are marked by the black and magenta diamonds, respectively. It can be seen in the figure that the HWRF storm centers (i.e., the eyes) were coincident with the magenta diamond (the initial HWRF storm centers) in Figure 8a,b (the HWRF wind fields before shifting was performed). In Figure 8c,d, the resampled HWRF 2D wind fields have been shifted so that their storm centers were coincident with the location of the satellite storm center (the black diamond).