In 3 consecutive years from 2016 to 2018, extreme ocean warming events, or marine heatwaves (MHWs), occurred during boreal summers in the East China Sea (ECS) and South Yellow Sea (SYS), which is unprecedented in the past four decades based on the satellite record. In this study, we used a high-resolution hydrodynamic model based on Finite Volume Community Ocean Model (FVCOM) to simulate the evolution of these warming events. An upper ocean temperature budget (0-20 m) analysis based on the model results shows that the shortwave radiation and the ocean advection anomalies jointly contributed to the anomalous warming in the three successive summers (June-August) in the SYS and the north part of the ECS. In addition, the reduction of surface wind speeds during the 2016 and 2017 summers further weakened the vertical mixing, thereby enhancing the anomalous warming in the north part of the ECS adjacent to the SYS. During the three summers, the increases of shortwave radiation were closely related to the East Asian Summer Monsoon (EASM) variability, which reduced the cloud cover in the ECS and SYS, whereas the advection anomalies were mostly associated with regional wind anomalies. In summer 2018, upper ocean heat was transported into the central trough of the SYS, accumulated in an anticyclonic eddy generated by the anomalous wind stress curls. Therefore, despite the primary driver of the MHWs is the EASM variation, regional processes are critical to driving the spatial pattern of the MHW intensity in the ECS and SYS.Plain Language Summary Marine heatwaves, known as periods of extreme warming at the sea surface, can last for days to months and cause damages to the marine environment and marine life. In the East China Sea and the South Yellow Sea, the frequent occurrences of harmful algae blooms are often associated with marine heatwaves. Satellite data reveal that marine heatwaves occurred in the East China Sea and the South Yellow Sea during the three boreal summers from 2016 to 2018, which is unprecedented in the past four decades. Using a numerical model of the ocean, we examined the marine heatwaves during these three successive summers. We show that the increased solar radiation, ocean current anomalies, and reduced vertical mixing were three critical factors for the warming events in the three summers. This study helps the fisheries and aquaculture industries in the East China Sea and the South Yellow Sea to better manage the environmental risks under a warming climate by predictions of marine heatwaves.

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