This paper presents an observational analysis performed with data from the Pacific Decadal Oscillation (PDO) index and seasonal precipitation during the rainy season in Belém during the years 1925 to 2011. Since the focus of the present work is on rainy season, we selected consecutive months in which is observed maximum monthly rainfall volume: (January to April - JFMA). From the original monthly ODP data (January to December) it was generated a seasonal ODP index corresponding to the October to March (ONDJFM), where was evidenced: PDO warm phase between the years 1925 and 1944. PDO cold phase between the years 1945 and 1976, PDO warm phase between the years 1977 and 1998, and the beginning of the PDO cold Phase from 1999 to 2011. The results showed that during the PDO warm phases there is a predominate of SST positive anomalies over the east-central tropical Pacific that are related to configuration of El Niño events, which are associated with the presence of negative precipitation anomalies, particularly in eastern Amazon and Northeast Brazil. Conversely, during the PDO cold phases we observed areas with SST negative anomalies over the central sector and eastern tropical Pacific, which are related to the La Niña events, which induce positive precipitation anomalies over north and northeast sectors of South America, including the eastern Amazon and Northeast Brazil. In this context, it was shown that the ODP phases exert impacts on seasonal precipitation in eastern Amazon, sometimes with a significant reduced rainfall, sometimes with enhanced rainfall particularly in Belém.
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