Combined effects of ENSO and PDO on activity of major hurricanes in the eastern North Pacific

Major hurricanes (MHs) in the eastern North Pacific (ENP) in 1970-2020 are clustered into 3 categories with different quantity, intensity, lifetime, and track. MHs in all three clusters are more active in the Pacific Decadal Oscillation (PDO) warm than cold phases. However, only the relationship between MHs in the western part of ENP (cluster A) and El Nino Southern Oscillation (ENSO) is significantly modulated by the PDO. This cluster is more active during El Nino than La Nina years in the PDO cold phases, which results from the local sea surface temperature (SST) warm anomalies caused by the combined influences of ENSO and the PDO. Warmer SST can make a stronger ascending flow, and strengthen the local activity of MHs by leading to anomalous atmospheric circulation. In the PDO warm phases, however, there is no distinct local SST anomalies between two ENSO phases. Therefore, the modulation of PDO on ENSO and cluster A only occurs in the PDO negative phases. In the region of the eastern part of ENP where two other clusters are located, the PDO hardly modulates the relationship between ENSO and MHs activity as the PDO exerts little influences on the ENSO-related SST patterns in both the positive and negative phases. The conclusion is also supported by first mode of empirical orthogonal functions analysis for interannual MHs activity. Therefore, the PDO modulation cannot be ignored when predicting the activity of tropical cyclones in the ENP, especially for MHs with strong wind and rainstorm.