Tropical cyclone frequency in the Central North Pacific (CNP) from 1966 to 2000 has undergone decadal-scale variability. A statistical change-point analysis reveals objectively that the shifts occur in 1982 and 1995, with fewer cyclones during the 1966-1981and 1995-2000 epochs and more during the 1982-1994 epoch. A bootstrap resampling method is then applied to determine the frequency distribution of the mean annual cyclones for each epoch (1966-1981 and 1982-1994), as well as to infer the confidence intervals of the observed mean and variance of the cyclones for each epoch.

Large-scale environmental conditions conducive to cyclone incidences during the active hurricane season (July through September) are investigated. In contrast to the first epoch (1966-1981), warmer sea surface temperatures, lower sea-level pressure, strong lower-level anomalous cyclonic vorticity, reduced vertical wind shear, and increased total precipitable water covered a large domain of the tropical North Pacific in the recent epoch (1982-1994). These changes in the environmental conditions favor more cyclone incidences since 1982. Many of the aforementioned changes were already established prior to the active season. In addition, atmospheric steering flows have changed remarkably in October and November so that tropical cyclones in the Eastern North Pacific have a better chance to enter the CNP, and cyclones formed in the CNP are more likely to be steered through the western Hawaiian Islands in the recent epoch.