We examined the sea surface temperature (SST) distribution in the western North Pacific warm pool when a typhoon is generated in northern summer. Analyzing satellite observation data revealed higher (lower) SST north (south) of the typhoon. As a result, the meridional SST gradient became especially steep, and the SST was not homogeneously high, when a typhoon is generated. In-situ observation data in the oceanic surface layer suggested that the low SST was caused by vertical mixing related to the strong southwesterly monsoon. In contrast, the hot spots north of the typhoon were associated with weak sea surface wind and vertical mixing. According to satellite observation, the maxima of surface heat flux and water vapor shifted northward corresponding to the high SST. They may produce an asymmetry of the thermodynamic structure of a typhoon.