Sea surface temperature (SST) harmonic and empirical orthogonal function (EOF) analyses covering 18 years were performed for the area located from 114°to 105°W and from 18°to 25°N. The results indicate that the influence of the annual signal predominates over the semiannual signal, and the closer to the coast, the stronger the annual harmonic. Several interannual anomalies arose that are connected with the main global indexes, especially the Oceanic Niño Index. Pearson correlations between the first temporal mode of the SST and regional rainfalls in Nayarit indicate that maximum correlations (r>0.7) are observed when there is a +1-month lag between the series. However, this result indicates that SST is delayed with 1 month after rainfall occurrence, which shows that the dominant influence in this relationship is not the SST forcing.