# Assessment of CYGNSS Wind Speed Retrievals in Tropical Cyclones
## 5 Wind Assessment in Tropical Cyclones
### L3 CYGNSS Storm-Centric Winds
The scatterplot of AMSR2 versus CYGNSS (c) is very similar to the one for HWRF versus CYGNSS (d), with CYGNSS underestimating winds above 30 m/s, and displaying a noisy and irregular storm structure. For comparison, the scatterplot of AMSR2 versus HWRF (e) shows a very good consistency between the two products. Figure 13: (**a–i**) Time series of selected scenes from the CYGNSS Storm-Centric V1.0 dataset for Hurricane Florence in September 2018. Only scenes with sufficient coverage of the storm are displayed, defined by at least 1000 valid grid points (0.1\({}^{\circ}\)\(\times\) 0.1\({}^{\circ}\)). The best data coverage is on 11 September at 1800 UTC (**d**) and 12 September at 1800 UTC (**f**). The last case study illustrated here, in Figure 17, refers to a storm where the CYGNSS storm-centric winds are systematically higher than the radiometer winds: Hurricane Leslie on 3 (0600 UTC) and 11 October (0600 UTC) for which AMSR2 and SMAP data are available within 4 h. Despite the systematic bias, on 3 October, the CYGNSS storm-centric data display a wind field structure very similar to the one observed by AMSR2, with a clear eye, and the highest winds in the NW quadrant. This helps illustrate the potential of the storm-centric CYGNSS dataset that could be achieved by aggregating de-biased CYGNSS L2 data. In contrast, the comparison with SMAP on 11 October shows a less than ideal match between the two wind fields, in terms of storm structure and average bias. The analysis presented here suggests that the creation of a storm-centric CYGNSS dataset has great potential for storm forecasters, but the product is still in the early stages of development. A similar storm-centric dataset aggregating the NOAA V1.1 would likely be of much better quality, but it has not been developed yet. Figure 14: Comparison of CYGNSS storm-centric surface wind field (**a**,**d**) versus the HWRF model (**b**,**c**), with the original CYGNSS data at a resolution of 0.1\({}^{\circ}\) compared to HWRF resampled at 0.1\({}^{\circ}\) (**a** versus **b**), or both resampled at 0.25\({}^{\circ}\) (**c** versus **d**), for Hurricane Florence on 11 September 2018, 1800 UTC. A pass from the AMSR2 radiometer at 1730 UTC, on a 0.25\({}^{\circ}\) grid is also displayed (panel (**e**)). The bottom panels display the respective scatterplots for HWRF versus CYGNSS for the two resampling cases (**f**,**g**) and for HWRF versus AMSR2 (**h**). Figure 16: Comparison of a CYGNSS storm-centric scene at 6 UTC (**a**) with AMSR2 TC-winds observed at 07:37 UTC (**b**), and a scatterplot of their colocations (**c**) for Hurricane Michael on 10 October 2018. Panels (**d**,**e**) display the scatterplots for the resampled HWRF versus CYGNSS storm-centric winds and versus AMSR2 for the same scene. Figure 15: Similar to Figure 14 panels c–e (**a–c**) and g,h (**d**,**e**), but for another time frame (12 September, 12 UTC) in the CYGNSS storm-centric dataset resampled at 0.25\({}^{\circ}\) in a Hurricane Florence scene with good temporal colocation with SMAP (11 UTC).