Tropical cyclone (TC) activity during the period from 1979 - 2010 represented by the Emanuel-Nolan “genesis potential index” (EN-GPI) is compared and evaluated against observation of TC records over the North Atlantic and the western North Pacific. This study shows that, while the EN-GPI might be a nice proxy in reproducing major climatic features of TC activity (e.g., spatial genesis pattern and seasonal cycle), its performance in representing the interannual TC variability appears to be highly basin-dependent, with a skillful performance over the North Atlantic, but not over the western North Pacific. A term budget analysis of the EN-GPI, along with a number of designed sensitivity experiments, clearly points out that such a huge performance contrast between the two ocean basins must come from a spurious estimation of the “maximum potential intensity” (Vpot) term over the western North Pacific for its magnitude being too sensitive to change of SST compared with that over the North Atlantic. A refinement of the EN-GPI according to regional climate conditions is advised to projecting the long-term TC activity, in particular, over the western North Pacific.