AbstractA regional ocean model simulation for the period from 2000 through 2016 is used to study oceanic wave propagation in the Indonesian seas. The model simulation compares favorably with the interannual variability of the satellite derived sea level anomaly and the observed currents in the entrance passages of ITF. Lag correlation analysis suggests that the interannual sea level anomaly and opposite responses of the velocity above and below the thermocline in the western (the Sulawesi Sea and the Makassar Strait) and eastern (the Halmahera Sea) pathways of ITF are associated with the ENSO induced Rossby waves from the equatorial Pacific rather than the local wind forcing. In particular, during La Niña years ENSO induced anomalies traveling through the western pathway are comparable to those through the traditional eastern waveguide, suggesting the importance of both pathways in the propagation of ENSO signals in the Indonesian seas. Different roles of the western and eastern pathways in transmitting the ENSO signals into the Indonesian seas are associated with the nonlinear processes in the Sulawesi Sea, which appears to be linked with different states of the western boundary currents during the warm and cold ENSO phases.