## 2 Methodology
### Developing Hindcast WST  
Australian meteorological hindcast data were used to develop standard and local/seasonal WSTs for sea areas under consideration, i.e., the North Atlantic Sea, given that hindcast data are the most reliable source for historical weather data analysis. The Bureau of Meteorology (BoM), Australia, and the CSIRO have developed a hindcast model called the Centre for Australian Weather and Climate Research Wave Hindcast (CAWCR), which uses WAVEWATCH III, a numerical model, to provide higher-resolution global meteorological data. The model has been well-validated and updated over the years [24]. It has undergone two updates in the past, and since June 2013, no significant configuration change has been made to the model. The data available have 0.4-degree spatial and hourly temporal resolution for the global data. The spatial resolution is higher for the region around Australia. For this study, the data from June 2013 to March 2022 with a spatial resolution of 0.4 degrees are used. The CSIRO provides free access to the hindcast model through the CSIRO data server. The server is populated monthly with the previous month's hindcast file [7]. The monthly files (netCDF file format) required for the study were downloaded to the local system and striped for parameters shown in Table 1 for the North Atlantic Sea. The temporal data of the North Atlantic Sea area were saved under individual sea area numbers, i.e., 8, 9, 15 and 16, to reduce the size of individual files. To further reduce the size of the file and for fast processing, each monthly sea area file was reduced to a monthly WST for wind, swell and mean sea using an in-house-developed algorithm. The algorithm is capable of developing WSTs for customised sea regions, including customised time for wind, swell and mean sea. The individual monthly WST is a 25 by 25 matrix and is stored in a structured format to m.files, which is used for further analysis in this study. The data set developed is a simple way of looking into the sea state contribution of swell, wind and mean sea. The monthly data are sorted as a function of wave height and zero-crossing wave period, and the occurrence of each state is counted to the respective matrix (mean, wind and swell). The matrix has unit meter and unit period resolution. The following data points are considered for generating a WST: significant wave height (hs) and mean period of first frequency moment (t01), significant wave height of wind sea (ph80) and peak period of wind sea (ptp0) and significant wave height of primary swell (phs1) and peak period of primary swell (ptp1). The combinations of the above parameters make the mean sea WST, the wind sea WST and the swell sea WST as given in Table 1. Equations (1) and (2) are used to estimate the zero-crossing wave period, since it is not directly available from the peak and mean wave period. The CAWCR wave model uses the JONSWAP wave model to develop the hindcast wave model [7]. The developed matrix is called the local hindcast WST. \[\frac{T_{z}}{T_{P}}=0.6673+0.05037\gamma-0.006230\gamma^{2}+0.0003341\gamma^{3} \tag{1}\]  
\[\frac{T_{1}}{T_{P}}=0.7303+0.04936\gamma-0.006556\gamma^{2}+0.0003610\gamma^{3} \tag{2}\]  
where \(T_{z}\) is the zero-crossing period, \(T_{1}\) is the mean period, \(T_{p}\) is the peak period and \(\gamma\) is the peak shape parameter (\(\gamma\) = 3.3). From the monthly local hindcast WST, the annual and seasonal WSTs are developed by summing the monthly WST for respective months. The seasonal and annual WSTs are then