The modulation of tropical cyclone (TC) genesis over the western North Pacific (WNP) by the intraseasonal variability (ISV) is investigated in this study. The two leading ISV modes, i.e., the 40-day Madden-Julian oscillation (MJO) and the 16-day quasi-biweekly oscillation, are found to exert significant impacts on TC genesis over the WNP. A majority of TC geneses over the WNP is found to occur during the period when both the modes are active, suggesting a joint influence of the two modes on TC genesis over the WNP.
 The modulation of TC genesis over the WNP by the two leading ISV modes can be well depicted by the genesis potential index (GPI). Contributions of the four terms to the total GPI anomalies are further analyzed to determine the key factors involved in modulations of TC genesis by both of the ISV modes. Results indicate that while, in general, the low-level absolute vorticity and the mid-level relative humidity are the two most important factors affecting WNP TC genesis, relative roles of the four GPI factors also tend to be dependent on the ISV phases. This study provides further understanding of the ISV modulation of WNP TC genesis, which could benefit the intraseasonal prediction of the TC activity.