Intraseasonal variations constitute a significant part of the variability in the Indonesian Seas, which modulate the Indonesian Throughflow, as well as the regional weather and climate. This study employs a regional ocean circulation model to investigate the pronounced 30-120 day variability along the Sumatra-Java-Lesser Sunda coasts and into the Banda Sea. The model simulations depict three prototype events: For Type-1, strong westerly winds in the equatorial Indian Ocean generate eastward Kelvin waves and promote water accumulation along the Sumatra coast, forming a southeastward geostrophic current that enhances signal propagation into the Banda Sea. Meanwhile, the Banda Sea is under the control of easterly or southeasterly wind anomalies, which induce downward Ekman pumping and positive Sea Surface Height Anomalies (SSHA) to facilitate continuous signal propagation in the southern Banda Sea. For Type-2, the equatorial wind forcing is weak, and the Kelvin wave amplitude is relatively small. During the later stage, local winds over the Banda Sea generate offshore Ekman transport and upwelling, leading to a decrease in SSHA and thereby hindering signal propagation in the Banda Sea. Type-3 events show no continuous propagation. Although the equatorial wind forcing favors signal propagation from Sumatra to Lombok, local winds exert a suppressive effect throughout the event, weakening coastal SSHA response and blocking the transmission east of Lombok. These results highlight the importance of cooperation and interference between remotely and locally generated signals in governing the intraseasonal variability in the interior Indonesian Seas.
 

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