Short period modulations of less than one month are studied for M₂ tidal waves in water level records taken from the Gran Canaria Island Shelf off the island’s east coast). From the relation ship among modulations with low frequency oscillation observed in this zone (Bruno, 1993), a mechanism based on non-linear interactions of meteorological low frequency oscillation and M₂ signal is proposed. This interaction explains a large amount of residual semidiurnal variance in the water level data.