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In August 2020, the historical warmest upper‐ocean thermal condition occurred in the western North Pacific (WNP), along with three tropical cyclones (TCs, namely Bavi, Maysak, and Haishen) generated in the WNP and affected Northeast China and the Korea peninsular (KP), within an unprecedentedly short span of 12 days from late August to early September of 2020. Meanwhile, prior to the formation of Bavi, a series of extreme warm mesoscale oceanic eddies were also observed over the WNP, and clearly sea surface cooling was detected after the passage of the three TCs. However, it remains unknown whether the warmest WNP with extreme warm mesoscale oceanic eddies has a modulation effect on intensity change of the three TCs. The results of sensitive experiments with fixed atmospheric initial conditions revealed that the historically warmest upper‐ocean thermal condition in the WNP in August 2020 might have contributed to increasing the intensity of three TCs by 5.3–10.0 hPa compared to normal ocean thermal conditions. The simulation results indicated that the extreme warm mesoscale eddy conglomeration might assist in intensifying the three TCs when they passed over these warm mesoscale eddies. Whereas the cold wake over the East China Sea caused by preceding TCs, Bavi and Maysak, might partly aid in weakening subsequent TCs in the decaying period. Furthermore, the simulated bias in the intensity evolution of the three TCs and the possible cause of minor differences in the simulated tracks and large‐scale steering flow between the sensitive and control experiments were discussed. Plain Language Summary: In summer 2020, three typhoons hit Northeast Asia in an unprecedented 2‐week period. Using the COWAST model we investigated the possible effect of the historical warmest upper‐ocean thermal condition with preexisting extreme warm mesoscale eddies in the western North Pacific (WNP) on the three tropical cyclones, as well as the cold wake induced by preceding tropical cyclones (TCs) on subsequent TCs. The results indicated that the WNP's warmest upper ocean thermal condition might enhance the three TCs, whereas the preexisting warm mesoscale eddy conglomeration and cold wake caused by preceding TCs might partly affect the intensification and decay of Maysak and Haishen. Key Points: Three typhoons affected Northeast Asia within a short span of 2 weeks in 2020 over the warmest upper ocean of the western North Pacific in historyThe historical warmest upper ocean thermal condition in 2020 may increase the intensity of the three tropical cyclones (TCs)Pre‐storm warm‐core eddy conglomeration and cold wake induced by preceding TCs partly influenced intensity evolution of Maysak and Haishen [ABSTRACT FROM AUTHOR]