Using the tropical cyclone best track data from the U.S. Department of Defense's Joint Typhoon Warning Center (JTWC), Webster et al. [2005] found that between the two consecutive 15-year periods of 1975–1989 and 1990-2004, the percentage of typhoons in the western North Pacific meeting the definition of categories 4 and 5 on the Saffir-Simpson Hurricane Scale has increased from 25% to 41% of all typhoons in that ocean basin. However, an analysis of the best track data from the Regional Specialized Meteorological Centre (RSMC) Tokyo (Japan) as well as that of the Hong Kong Observatory (HKO; Hong Kong, China) indicates that, in contrast to Webster et al.'s [2005] findings, there was no increase in western North Pacific category 4–5 typhoon activity. Furthermore, neither RSMC-Tokyo nor HKO best track data suggest an increase in western North Pacific tropical cyclone destructiveness as measured by the potential destructive index (PDI).