Elucidating the mechanism that determines the number of tropical cyclones (TCs) is fundamental for understanding variations in TC activity and predicting future changes. An average of about 80 TCs form each year around the world, with the exact number varying interannually and seasonally (Gray, 1968;Schreck et al., 2014;Webster et al., 2005). Although these variations have been described in relation to large-scale environmental fields represented by a genesis potential index (Emanuel & Nolan, 2004;Gray, 1975;Murakami & Wang, 2010;Tippett et al., 2011), such a relationship does not necessarily hold for future global warming conditions (Camargo et al., 2014). Davis et al. (2008) proposed focusing on pre-TC vortices to clarify how large-scale conditions affect cyclogenesis efficiency. The modulation of TC frequency by the Madden-Julian Oscillation (MJO) is more attributed to tropical depression (TD) frequency than to the probability of TDs intensifying in the western Pacific and the Indian Ocean (Duvel, 2015;Liebmann et al., 1994), though TDs are relatively mature. Recent studies considered TC frequency as the product of the number of weak pre-TC vortices (TC seeds) and the percentage of TC seeds that develop to TCs (survival rate), and proposed that this framework could help to uncover the mechanism behind the variation in TC frequency (Sugi et al., 2020;Vecchi et al., 2019;Yamada et al., 2021). To determine the change in TC frequency due to global warming, for example, it has been suggested that the change in TC seed frequency is most important (Sugi et al., 2020;Vecchi et al., 2019). However, an analysis of results from multiple high-resolution models showed that the contribution of survival rate to TC frequency cannot be ignored (Yamada et al., 2021). Such analyses of TC frequency have more