In this work, they were studied the components of the averages of annual rains of the state of the Rio Grande do Sul, starting from 28 grating points contained in four defined homogeneous areas by the analysis of groupings. The data followed normal distribution approximately and they presented homogeneous variations, could be analyzed directly without, without need of a previous transformation. The periodogram of the annual averages of each group allows establishing models of 3 sinusoidal waves. The waves of periods 5, 3,8 and 3,3 years stood out in 75% of the models. The models represent the behavior of the data appropriately and in a satisfactory way they allowed the forecast of future values.