The surface temperature of the Uma-shima Strait of the eastern coast of Suo Nada, Yamaguchi, Japan, was monitored every month from 1987 to 2010 and temporal trends were analyzed using Ordinary Least Squares regression analysis. The annual average temperature increased at a rate of 3.31×10^{-2} ℃/year during this period, with more pronounced monthly patterns in August, October, and November. Similar patterns were observed in the temperature data recorded at air and water monitoring stations located nearby. Analyses of these records using regressions demonstrated that the surface temperature of the water of Uma-shima Strait water is influenced by the properties of the atmosphere and the water mass of the offshore area and that this influence varies from season to season with five distinct phases: an aircorrelated phase（April)； an air-correlated and water-altered phase（August–October)； a water-correlated and air-altered phase（January–March)； a water-correlated phase（May and November)； and an uncorrelated phase（June-July and December).