Kagoshima Bay is an enclosed bay that has the tendency to undergo eutrophication, and a very important site to describe the behavior of open seawater intrusion. According to the results of the satellite SST (Sea Surface Temperature) image analysis or numerical simulation focused on the warm water intrusion into the bay in winter, a warm water mass originates in the meandering Kuroshio Current and reaches the mouth of the bay making the density flow to act like a semi-geostrophic current that is influenced by the Coriolis effect. However, there is still no information on the oceanic intruding flow during the summer, where it is accompanied by thermal stratification. In this research, satellite remote sensing and numerical simulation were employed to investigate the oceanic water intrusion into Kagoshima Bay during the summer season by using satellite chl-a (chlorophyll-a) images instead of SST. As a result, the distribution of the low-concentration chl-a with the oceanic water intrusion was found to be similar to the intrusion that occurs during the winter season. Furthermore, the numerical simulation was performed under the simple assumption that the thickness of the warm water mass that reaches the southern coast of Kyushu also shows the same tendency as in the winter season. Although the characteristics, such as the intruding speed or intruding pattern, are similar in winter, some features such as the generation of the inflow from the middle layer, showed a different tendency.