<p>El Niño is widely regarded as a key modulator of the summer tropical cyclone (TC) activity in the Northwest Pacific (NWP). However, the critical role of El Niño decaying rate in the TC genesis frequency in the NWP during its second summer remains poorly understood. Utilizing the observational and reanalysis datasets from 1970 to 2023, this study reveals a significant difference in the TC genesis frequency in the NWP between the short-duration (SD) and long-duration (LD) El Niño decaying summers. The SD El Niño events induce an average reduction of about 3 TCs (~ 25%) in the NWP during the decaying summers compared to climatology, while the LD events show no statistically significant TC genesis frequency anomalies. This is closely associated with the difference of large-scale circulation between the SD and LD El Niño decaying summers. During the SD El Niño decaying summers, significant warm sea surface temperature anomalies (SSTA) over the northern Indian Ocean along with the cool SSTA over the tropical central Pacific trigger and sustain an anomalous anticyclonic circulation in the NWP, effectively suppressing the local TC genesis. In contrast, in the LD El Niño decaying summers, the insignificant SSTA over the northern Indian Ocean along with the weak but warm SSTA over the tropical central Pacific fail to generate persistent atmospheric circulation anomalies in the NWP, resulting in no significant impact on the local TC frequency. In particular, this work reveals that the mid-tropospheric vertical motion associated with the large-scale circulation emerges as a dominant environmental factor controlling the TC frequency difference in the NWP between these two-type El Niño decaying summers. These findings advance our understanding of the influence of the El Niño decaying temporal characteristics on the tropical climate variability, with particular implications for the seasonal TC activity prediction in the NWP.</p>