# Tropical Cyclone Winds from WindSat, AMSR2, and SMAP: Comparison with the HWRF Model
## Methods
### Time Interpolation
Once this shifting was performed, the HWRF data could be interpolated to the time of the satellite overpass. This was done by taking a weighted average of the two resampled HWRF wind fields surrounding the satellite observation, with more weight applied to the HWRF winds that were closer in time to the overpass. The steps of this shifting methodology can be summarized as follows and can be applied to any high-resolution data set, such as HWRF, when comparing it to satellite data in tropical storms:  
Figure 8: Top panels: The resampled HWRF winds at model times before (**a**) and after (**b**) the SMAP pass over Typhoon Mangkhut on 15 September 2018 at 22:34 UTC before spatial shifting was performed. Bottom panels: The resampled HWRF winds at model times before (**c**) and after (**d**) the SMAP pass after spatial shifting was performed. The SMAP storm center is indicated by the black diamond. The original HWRF storm center is indicated by the magenta diamond. Resample the high-resolution data to the same spatial resolution as the satellite (Section 3.1). Shift the resampled storm winds at the model times surrounding the satellite pass so that their storm centers align with the storm center as seen by the satellite. Linearly interpolate the model wind field to the same time as the satellite pass. The result of using this methodology on the HURF winds surrounding the SMAP pass of Typhoon Mangkhut on 15 September 2018 is shown in Figure 9. It is clear that the resulting HURF wind field is more realistic than the one obtained from interpolating un-shifted winds (Figure 7a), and the double-eye feature is no longer present. It also compares better to the SMAP winds for this pass (Figure 7b). For instance, the location of the maximum winds in the NE quadrant in Figure 9 is more in line with their location as seen by the satellite. We also noted that the value for the maximum intensity (43 m/s) agreed better with the SMAP intensity (42 m/s) than if no shift was performed (39 m/s). There are still differences between the resampled and shifted HURF field and SMAP, but the comparison is clearly better than without aligning the storm centers. Another example of this shifting methodology is shown in Figure 10 for a WindSat pass over Hurricane Teddy on 19 September 2020. It can be seen that shifting the surrounding HURF wind fields first (Figure 10b) removed the double-eye feature present in the original interpolation method (Figure 10a). The storm structure when the shifting was used corresponded much better with the WindSat field than in the unshifted case. For example, the locations of the eye and the relative maxima of winds in the eye wall in the NW, NE,  
Figure 9: The resampled HURF wind field to be compared with the SMAP pass over Typhoon Mangkhut on 15 September 2018 created by first shifting the surrounding HURF winds before interpolating. and SE quadrants in the shifted wind field are now in approximately the same location as they were in the satellite wind field. It should be noted that using this shifting methodology generally provides the most improvement in cases where a more well-organized storm has moved rapidly between two analysis times. In other cases; i.e., if the storm is less organized and/or slower moving, or if one is interpolating between two times that are closer than 6 h apart (e.g., 3 h), the relative improvement provided by shifting the surrounding HWRF storm centers to the satellite storm center is small or negligible. The use of this methodology also does not generally have a large effect on overall statistical comparisons of satellite and model winds, particularly in cases with many matchups.