Western North Pacific tropical cyclone intensity and ENSO

The influence of the El Nino-Southern Oscillation (ENSO) on tropical cyclone intensity in the western North Pacific basin is examined. Accumulated cyclone energy (ACE), constructed from the best-track dataset for the region for the period 1950-2002, and other related variables are analyzed. ACE is positively correlated with ENSO indices. This and other statistics of the interannually varying tropical cyclone distribution are used to show that there is a tendency in El Nino years toward tropical cyclones that are both more intense and longer-lived than in La Nina years. ACE leads ENSO indices: during the peak season (northern summer and fall), ACE is correlated approximately as strongly with ENSO indices up to six months later (northern winter), as well as simultaneously. It appears that not all of this lead-lag relationship is easily explained by the autocorrelation of the ENSO indices, though much of it is. Interannual variations in the annual mean lifetime, intensity, and number of tropical cyclones all contribute to the ENSO signal in ACE, though the lifetime effect appears to be the most important of the three.