The ocean/atmosphere interaction is commonly studied through processes orphenomena such as El Nino / Southern Oscillation (ENSO). Many of the statisticalstudies on the subject, focus on the use models for continuous time series,adjusting models in the time domain, as in the case of univariate or multivariateARIMA models. However, not always the primary concern is to determine exactlythe magnitude of climatic anomalies such as the amount of rainfall in a periodbut, categorizing the magnitude of precipitation, to determine the probabilityof occurrence of class, conditioning on different categorizations (i.e. terciles)of ENSO. The objective of this study is to find and / or develop methodologicalstatistical strategies to estimate these probabilities. In particular, we are interestedin assessing and modeling the relationship between the occurrence of El Nino (LaNina) and the variability of precipitation in the Central Region of Costa Rica, inMay-June-July season. Data are time series of sea surface temperature (SST) in thearea of Nino 3 and the Southern Oscillation Index (SOI) for atmospheric pressure.As the response we used rainfall (R) recorded in Juan Santa Maria airport, CostaRica. The series were categorized into terciles to build two-way contingencytables. The tables were analyzed using log-linear and proportional odds models,to determine the conditional and joint probabilities of rainfall events. We alsoestimated a measure of ordinal association.