## 6 Analysis of RAMS-ISAC Simulations  
The forecast of Medicare Numa was characterized by a significant change of the prediction of its position depending on the model initialization time. In an unstable flow regime, such as Numa, the sensitivity of the predicted storm features, for example the position of the cyclone eye, to the initial and boundary conditions is well known [5; 13]. Nevertheless, in this section we highlight important aspects related to an operational NWP model setup [13]. Here we analyze the operational RAMS-ISAC forecasts issued on 16 and on 17 November. The first operational forecast uses the Global Forecast  
Figure 12: Vertical cross-section of radar reflectivity observed at 80\({}^{\circ}\) azimuth by the GR in Pettinascura on 18 November at 04:00 UTC. GMI TBs at 37 GHz V-pol, 89 GHz V-pol, 166 GHz V-pol and 183.31+3 GHz are superimposed. System (GFS) analysis/forecast cycle issued at 12:00 UTC on 16 November as initial and boundary conditions, while the second forecast uses the GFS analysis/forecast cycle issued 24 h later at 12:00 UTC on 17 November. GFS initial and dynamic boundary conditions are downloaded at 0.25\({}^{\circ}\) horizontal resolution. The boundary conditions are updated every 6 h and the finalization date is +60 h after the initialization time. The sea surface temperature (SST) is interpolated onto the RAMS-ISAC grid from GFS analysis at 0.083\({}^{\circ}\) horizontal resolution. SST is constant during the simulation and it is that of the initial time of the simulation (12:00 UTC on 16 and 17 November, depending on the simulation). It is important to note that we do not consider the impact of rapidly generated sea waves on the sea surface roughness, which plays an important role for the exchange of energy and momentum between the sea surface and the atmosphere. The sea surface roughness is estimated by the Charnock relation [54], which increases with the square of the friction velocity. So, the sea surface roughness is higher for more intense surface winds. We used rain gauges to independently verify the accuracy of the forecasts. Based on rain gauges, the most abundant precipitation registered over land during the event was in the southern part of the Apulia region (Salento), between 12:00 UTC on 17 November and 12:00 UTC on 18 November. The Italian rain gauge network (Figure 13a,b) recorded 24 h precipitation varying from 64 mm/24 h of Corigliano d'Otranto (40.1\({}^{\circ}\)N, 18.3\({}^{\circ}\)E) to 172 mm/24 h of Presiece (39.9\({}^{\circ}\)N, 18.3\({}^{\circ}\)E), with the second largest precipitation (147 mm/24 h) in Ruffano (40.0\({}^{\circ}\)N, 18.3\({}^{\circ}\)E). It is worth noting that the mean annual (monthly) precipitation in Salento is -810 mm/year (~125 mm in November) and that the 17-18 November 2017 event was the most intense in terms of 24h cumulated precipitation since 1970 [55]. Figure 13: **(a)** Twenty-four hour rainfall (mm) measured by the Italian rain gauge network starting on 17 November at 12:00 UTC. Only rain gauges with rainfall larger than 0.2 mm/2h are shown. The first number inside the parentheses in the title shows the total available rain gauges for the time period, while the second number shows the rain gauges with precipitation larger than 0.2 mm/24 h; **(b)** same as in **(a)**, but with a zoom over Salento region (black box in **(a)**); **(c)** rainfall forecast for the 24 h ending at 12:00 UTC on 18 November for the simulation initialized on 16 November at 12:00 UTC; **(d)** same as (c) but for the simulations initialized on 17 November at 12:00 UTC. Figure 13c shows the 24 h precipitation predicted between on 17 November at 12:00 UTC and on 18 November at 12:00 UTC for the simulation starting on 16 November at 12:00 UTC. The amount of 100 mm/24 h is predicted over the Ionian Sea, with the maximum found 50 km south of the Apulia coast.