Significant wave height (sigH m) is traditionally defined as the mean of the highest third of the waves. It is defined spectrally as the square root of the zero order moment. In more colloquial terms, it corresponds to the wave height that you would perceive if you were at sea. It is a good representation of the severity of the wave field. Are there going to be larger waves than the reported significant wave height? Yes!, but the sigH m estimate is a good representation of the sea conditions.
Sea Surface displacement (ζ(t) m) is the total displacement of the sea surface relative to the mean sea level (which doesn’t include waves) driven by barotropic forcing (i.e. pressure). It is associated to the local tides and the global response to pressure effects (large scale wind effects moving water). In the LIS the sea surface displacement main tidal constituent is M2.
Dominant Wave Period (Tp s) is the period of the longest wave in the spectrum (long waves have longer periods and vice versa). The dominant wave corresponds to the largest wave in the wave spectrum. This is the most energetic wave present (longest, fastest). The wave field has many waves in the surface at once so in order to somewhat describe what is occurring, it is convenient to pick the dominant one.
Wind Speed Magnitude (m s-1) corresponds to the magnitude of the vectors that constitute the wind speed (u = f(x,y) in Cartesian coordinates). It shows how strong the wind is without directional considerations.