## 3 Results and Discussion
An average positive score of approximately 68%, ranging from 49% to 78%, was obtained for the WRF model, indicating a significant gain in accuracy for the TOMO solution across the entire domain. Relative to ERA5, an average positive SS of about 42%, ranging from \(-\)16% to 69%, was obtained. Notably, negative SS values in the southern part of the domain suggest ERA5's superiority in that location. The continuous evolution of the averaged tomographic vertical profile for WRF, ERA5, and TOMO for the month of August is shown in Figure 8. In the analysis above, both the WRF model and ERA5 exhibit a higher concentration of \(\rho_{p}\) near the surface. Throughout  
Figure 6: TOMO and models temporal evaluation using InSAR PWV maps as the “ground truth”. (**a**) mean RMSE; (**b**) mean BIAS; and (**c**) mean correlation coefficient. Before applying the statistical metrics, a spatial bilinear resampling method (that uses the distance-weighted average of the four nearest pixel values to estimate a new pixel value) was performed to attain the TOMO spatial resolution (9 km). Figure 7: Spatial evaluation using InSAR PWV maps. (**a**) Spatial RMSE for WRF; (**b**) for ERA5; and (**c**) for TOMO. (**d**) Skill score (SS) taking InSAR as “ground true”, WRF as first model, and TOMO as second; and (**e**) the same as before, but with ERA5 as the first model. The mean correlation and RMSE in kg/m\({}^{2}\) are within []. this month, the integrated values range between 40 and 60 kg/m\({}^{2}\), except for a few days coinciding with the Hurricane Harvey episode (indicated by dashed vertical lines). The vertical distribution of \(\rho_{v}\) is quite similar between the two models, but WRF tends to concentrate more moisture close to the surface, resulting in a more defined planetary boundary layer compared to ERA5 and TOMO. Remarkably, TOMO shows numerous similarities with the other two solutions. It captures significant oscillations, including short, dry, and wet episodes during extreme weather events. The vertical distribution of \(\rho_{v}\) aligns with the two models, with approximately 50% of water concentrated below 2000 m, maintaining consistent top levels as simulated by the models. Notably, the tomographic solution exhibits a diurnal oscillation, also observed at higher altitudes between 6 August and 26 August--this behavior is not simulated by the models but is confirmed by three GNSS-RO vertical profiles. Analyzing the full dataset, we verified that TOMO could capture the annual cycle of water vapor density, showing a less-noisy behavior when the wet season is established. An example of a vertical cross-section of the tomographic inversion for 22 August and 28 August at 00:00 UTC, corresponding to the southeast-northwest red dashed line in Figure 1, is shown in Figure 9. The tomography inversion shows some water vapor near the top of the domain during the Hurricane Harvey passage (see Figure 8 region between the vertical dashed lines and Figure 9c), only detected in this period, which could be an artifact in the tomographic inversion; however, validation remains challenging due to the absence of radiosondes or GNSS-RO observations during the hurricane event. Additionally, the TOMO results demonstrate striking similarities with WRF data, particularly on the 22 nd. Disturbances of humid air at upper levels originating from lower levels are clearly captured by WRF and tomography (Figure 9a,c). The heterogeneous humid atmosphere observed on day 22 can be linked to turbulent wind field conditions, coinciding with the more vigorous effects of the hurricane. In contrast, on day 28, steadier wind fields prevail at high speeds. On day 28, the tomography is quite close to ERA5. Taking TOMO as reference, the RMSE for the two instants in Figure 9 is 0.8 kg/m\({}^{2}\), the BIAS is 0.3 kg/m\({}^{2}\), and the correlation is 0.995. Compared with the WRF data, the RMSE and BIAS increased only by 0.2 kg/m\({}^{2}\), and the correlation decreased by 0.008.