Long-term trends and interannual variability in tropical cyclone activity over the western North Pacific

While Landsea et al. (1996) show that the number of intense Atlantic hurricanes is on the decrease, the trend of tropical cyclone activity over the western North Pacific is found to be just the opposite. For the period 1959 to 1994, the number of tropical storms and typhoons went through a period of decrease and then an increase, showing an obvious second-order variation such that the activity has been on a generally upward trend since the late 1980s. A similar trend is found for the number of typhoons. All these time tendencies are statistically significant. In addition to a trend, shorter-term oscillations of two, five and seven years can also be identified after the trend is removed.