During the last days of 2009 and the first days of 2010, a wide and deep low pressure system over Western Europe generated a very extended and strong southerly pressure gradient on the whole Western Mediterranean Sea with a resulting very rough to high sea state. Over the Ligurian Sea (North Western Mediterranean) the resulting sea state was a combination of a very tuned (in both frequency and direction) swell coming from the south-west, with nearly oceanic peak wave period, and a broader north-westerly wind sea with shorter period. This kind of sea state, not extreme in terms of significant wave height, caused unusual widespread damages to Ligurian coastal structures. In this study, authors investigated the structure of such a combined sea state by analysing numerical weather prediction outputs coming from atmospheric and wave models and comparing them with data coming from ondametric buoys and meteorological stations located in the Ligurian Sea area. As a result, it was found that the forecasting model chain almost correctly predicted the wave height in a first phase, when the sea state was only due to the first south-westerly swell peak, while significantly underestimated the combined sea state, when also the second north-westerly wind sea developed and interacted with the first one. By analysing the structure of directional wave spectra forecasted by the operational wave model and measured by the buoys, authors have attempted to find out the reasons for model deficiencies in forecasting the time evolution of significant parameters characterising the sea state.