## 5 Sea Conditions Analysis of the Sea Storm Event of 28 December 2020
The choice is based on the exposure of these two weather stations, on their relative proximity to the study area that is located along the line connecting WS-03 and WS-05. The real anemometric event, given by the average values of the two weather stations (Table 6), is transformed into a step diagram (Figure 13), composed of 14 sub-wind events, each of 60' in duration (from 06:00 to 19:00 UTC), with a constant wind speed equal to the average value in that specific time interval. Anemometric data (Figure 13) showed a freshening wind at constant direction, with wind speed that gradually increased from 06:00 UTC to 19:00 UTC without major changes. This almost linear progression allows for a linear interpolation of detected wind speeds over the entire duration of the event (14 h). Hence, it is possible to estimate the characteristic wave height by subtracting 25% of the amount of wind speed increase from the highest wind velocity reached at the end of the storm event and work on the obtained value [29]. The interpolated wind speeds span from 9.1 m s\({}^{-1}\) (t = 1) to 16.2 m s\({}^{-1}\) (t = 14) (see Figure 13); then:  
\[[16.2-0.25\ (16.2-9.1)]=14.4\ \text{m s}^{-1}. \tag{5}\]  
For the following analysis, we used a constant wind speed of 14.4 m s\({}^{-1}\) over a duration of 14 h.  
The reconstruction of the deep-water wave motion (offshore conditions) through the Dorrstein diagram (Figure 14), using the value above calculated (14.4 m s\({}^{-1}\)), allows estimating the characteristic wave height:  
- \(\text{H}_{\text{c}}=3.80\ \text{m}\),  
- \(\text{T}_{\text{c}}=7.3\ \text{s}\),  
- \(\text{H}_{\text{max}}=1.29\ \text{Hs}=4.90\ \text{m}\),  
These wave height values are confirmed by [PERSON] and [PERSON] (2007) wave growth nomogram (Figure 15), that allows evaluating the significant wave height in:  
H\({}_{8}\) = 3.80 m.  
The absolute maximum height is obtained by adding this value to the wave height recorded at the end of the previous anemometric event, assuming the principle of superposition of effects:  
H\({}_{\rm c,fin}\) = H\({}_{\rm c}\) + H\({}_{\rm s,fin}\) = 3.80 + 0.70 = 4.50 m,  
H\({}_{\rm I}\) = H\({}_{\rm max}\) + H\({}_{\rm s,fin}\) = 4.90 + 0.70 = 5.60 m. \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & & **Capo Posillipo** & **Port of Naples** & **Average** & \\  & & **ISMAR** & **ISPRRA** & **Value** & \\ \hline \multirow{2}{*}{**UTC**} & **Time** & **Avg. Was 1** & **Avg. Was 2** & **Avg. Was 1-2** & \\  & **Progr** & **(m s\({}^{-1}\))** & **(m s\({}^{-1}\))** & **(m s\({}^{-1}\))** & **Wind Dir** \\ \hline
06:00 & 1 & 4.9 & 9.4 & 7.2 & S \\
07:00 & 2 & 8.3 & 11.3 & 9.8 & SSW \\
08:00 & 3 & 6.0 & 11.9 & 9.0 & S \\
09:00 & 4 & 6.6 & 13.4 & 10.0 & S \\
10:00 & 5 & 9.0 & 16.6 & 12.8 & SSW \\
11:00 & 6 & 10.2 & 17.0 & 13.6 & S \\
12:00 & 7 & 10.1 & 17.3 & 13.7 & S \\
13:00 & 8 & 10.7 & 17.8 & 14.3 & SSE \\
14:00 & 9 & 11.5 & 16.9 & 14.2 & SSE \\
15:00 & 10 & 11.0 & 16.4 & 13.7 & SSW \\
16:00 & 11 & 10.1 & 16.9 & 13.5 & S \\
17:00 & 12 & 11.0 & 17.5 & 14.3 & SSW \\
18:00 & 13 & 11.5 & 18.5 & 15.0 & SSW \\
19:00 & 14 & 11.6 & 20.1 & 15.9 & SSW \\
20:00 & 15 & 8.8 & 4.6 & 8.5 & SW \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Wind event as sequence of hourly average wind speed at Capo Posillipo (ISMAR) and Port of Naples (ISPRRA) weather stations. Data are in reference to 28 December 2020. Figure 13: Hourly average anemometric values (Capo Posillipo and ISPRA-Port of Naples weather stations), with linear interpolation line (red values on the right). Wind direction changes are less than 30\({}^{\circ}\); hence, for simplicity, wave heights and periods are computed along a single (mean) direction. The data measured by the Massalubrense buoy of Parthenope University (Table 5) are significantly lower than the ones extracted from the Groen-Dorrestein nomogram. This depends on the smaller fetch as a consequence of the sheltering effect of Capri Island from S-SW winds. Conversely, when S-SW wind is active, unlimited fetches are available at via Partenope.