[1] The Main Development Region (MDR) for tropical cyclones (TCs) in the western North Pacific Ocean is the most active TC region in the world. Based on synergetic analyses of satellite altimetry and gravity observations, we found that the subsurface ocean conditions in the western North Pacific MDR has become even more favorable for the intensification of typhoons and supertyphoons. Compared to the early 1990s, a 10% increase in both the depth of the 26°C isotherm (D26) and Tropical Cyclone Heat Potential (TCHP) has occurred in the MDR. In addition, the areas of high TCHP (≥ 110 kJ cm−2) and large D26 (≥ 110 m) have 13% and 17% increases, respectively. Because these high TCHP and large D26 regions are often associated with intensification of the most intense TCs (i.e. supertyphoons), this recent warming requires close attention and monitoring.