The warm-season hydroclimatology stemming primarily from the monsoon and typhoons in East Asia is an important determinant of sustainable water supplies for coupled human and natural systems. Therefore, in this study, we develop an empirical approach to the separation of summer rainfall into typhoon and monsoon types. In addition, exploratory analysis is conducted for regional patterns of summer precipitation across the Korean Peninsula (KP) to determine changes in the various types of temperature gradient. The results show that atmospheric thermal transitions lead significant and consistent changes in rainfall during the boreal summer season (June–September) in South Korea. For positive land–ocean contrast years, statistically significant positive anomalies of summer precipitation were exhibited in the interior and eastern river basins. In contrast, for negative years, suppression of seasonal precipitation patterns was detected. Moreover, during years of positive meridional temperature gradient, summers tended to be wetter relative to the long-term average. Although the time window of typhoon impacts may vary for different episodic typhoon events, the obtained positive anomalies of seasonal precipitation were more significant after removing the effects of tropical cyclones over the KP.