Interannual variations of precipitation in several regions around the globe are known to be influenced by sea surface temperatures. We describe a procedure that elicits the same frequencies of variations in the sea surface temperatures as in precipitation. The modes of variation in the two fields are phase locked, allowing us to identify regions in the oceans that vary in unison with changes in precipitation on different time scales. The method is illustrated by application to the northeast section of Brazil, the Nordeste, where flood and drought occur frequently. ¿ American Geophysical Union 1993