A region with a low sea-surface temperature (SST) was identified in the western North Pacific (WNP) Intertropical Convergence Zone (ITCZ) or warm water pool region in boreal summer. The SST decreases by up to 0.5¿C from May to the June--July--August (JJA) season just east of Mindanao Island. Analyses of the observed data indicated that a northeastward surface current constantly exists throughout the year, supplying cold subsurface water through the Molucca Strait. As a result, the subsurface water is colder by several degrees compared with that in the surrounding regions. The sea-surface wind is strong over this region in the JJA season. Examination of Argo float data demonstrated that the mixed layer becomes deeper from May to the JJA season. It is suggested that the strong wind causes vertical mixing between the surface and subsurface layers, resulting in the low summertime SST.