## 5 Sea Conditions Analysis of the Sea Storm Event of 28 December 2020
For convenience, we consider 06:00 UTC as the onset time of the event, when the anemometric diagrams (Figure 8) indicate a significant increase of the wind speed. Wind intensification occurred during almost the entire morning and afternoon of 28 December 2020, until 19:00 UTC. In detail, two distinct wind corrid \begin{table}
\begin{tabular}{c c c} \hline \hline
**Dir (\({}^{\circ}\))** & **F\({}_{\text{g}}\) (Km)** & **F\({}_{\text{r}}\) (Km)** \\ \hline
190 & 327 & 327 \\
200 & 317 & 317 \\
210 & 644 & 460 \\
220 & 566 & 460 \\
230 & 672 & 460 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Geographical (F\({}_{\text{g}}\)) and reduced (F\({}_{\text{r}}\)) fetch. Figure 11: Map and diagram of fetch relative to P1 in Figure 10. Map highlights the reduction of fetch in the main wave exposure through the green circle. Corridor 1 is relatively wide and is characterized by high speed, SW winds, whereas corridor 2 is relatively narrow and is dominated by SSW winds. Both corridors pointed towards the southern coastal area of Lazio at 15:00 UTC while approaching the coasts of Campania. These corridors acted extensively on the fetches of the main wave exposure angle of P\({}_{1}\). The convergence of two different wave motions likely caused a concentration of the sea storm energy, with enhancement of wave motion and the possible development of rogue waves due to random interaction of the two distinct wave trains. The maximum development of wave action occurred around 19:00 UTC, following a drop in wind intensity when the waves became regular in their profile, and the wave breaking process started, mostly due to the interaction of wave motion with the seabed, without substantial contribute of windshear (Table 5). This setting favored the concentration of energy in the wave motion and a wave geometry with almost undulatory profile before the breaking process. At the beginning of the windstorm event (t = 0), we consider the wave motion in the Gulf of Naples equal to the one recorded by the Parthenope University ondametric buoy for the time interval before 06:00 UTC:  
* H\({}_{\text{s}}\) (m) = 1.00,
* T\({}_{\text{s}}\) (s) = 4.1 \(\rightarrow\) L = 25 m,
* Dir (\({}^{\circ}\)) = 264. The wave motion is the result of the previous meteo-marine phase, with the presence of swell waves of modest steepness (low ratio H/L), as confirmed by the analysis of the Groen-Dorrestein [28]. In fact, a new forming wave characterized by a height H = 1.00 m, is characterized by a period T < 4 s (and shorter wavelength) for duration of the wind event D < 24 h. This is up to the intensity of 30 m s\({}^{-1}\), with delayed times for reaching the height of H = 1.00 m, depending on the intensity of the wind event and the delayed minimum fetch. The swell height usually decays about 25% in 12 h, and 40% in 24 h [29]. Given the duration of 14 h for the analyzed wind event, we consider that the initial wave motion, after 14 h, is reduced by 30%, as shown in Equation (4). \[\text{H}_{\text{s,in}}\ (\text{t}=0)=1.00\ \text{m}\rightarrow\text{H}_{\text{s,fin }}\ (\text{t}=14\ \text{h})=0.70\ \text{m}. \tag{4}\]  
Figure 12: Meteorological map (GFS Operational 0.250\({}^{\circ}\)) valid on 28 December 2020-H05:00 UTC for 10 m wind (kt). There is chromatic evidence of winds with gale force. For explanation of 1 and 2 corridors see the main text. Downloaded by www.wetterzentrale.de, accessed on 6 September 2021. The starting of the anemometric event induces the formation and the progressive development of new waves. According to the different period of the characteristic waves (previous and recent waves), the sea surface appears rather chaotic, with irregular distribution of waves with various height and period, but, as the waves grow, the development of characteristic waves is observed. The meteorological stations selected for the analysis of the anemometric event and used to evaluate the meteo-marine conditions in front of Via Partenope, are Capo Posillipo-ISMAR (WS-03) and Port of Naples-ISPRA (WS-05) (Figure 2).