This manuscript investigates the mechanisms controlling the transition into the equatorial Congo Basin’s biannual rainy seasons. It leverages satellite observations, water vapor isotopic data, and reanalysis to diagnose how moisture transport and atmospheric instability evolve in the weeks leading up to rainy season onsets. The topic is scientifically important and timely, as the processes initiating rainy seasons in this region have been poorly understood. The analysis is comprehensive and yields interesting results, notably that increased low-level Atlantic inflow and mid-tropospheric moistening appear to trigger the onset of deep convection in both spring and fall. Overall, this study provides important analyses, but several issues should be addressed to strengthen the manuscript.

Specific comments:

1. While the study is thorough, some findings (e.g., the importance of Atlantic moisture influx and mid-level moisture convergence for convective onset) are not entirely surprising in light of prior studies. For example, it was already recognized that near-surface divergence and mid-tropospheric moisture convergence play a role in equatorial rainfall (Nicholson 2018; Pokam et al., 2014). The manuscript would benefit from a discussion to demonstrate the unique contribution. 

Nicholson, S. E. (2018). The ITCZ and the seasonal cycle over equatorial Africa. Bulletin of the American Meteorological Society, 99(2), 337-348.

Pokam, W. M., Bain, C. L., Chadwick, R. S., Graham, R., Sonwa, D. J., & Kamga, F. M. (2014). Identification of processes driving low-level westerlies in west equatorial Africa. Journal of Climate, 27(11), 4245-4262.

2. The study’s reliance on reanalysis and satellite datasets may raise concerns about data uncertainty. The equatorial Congo is data-sparse, and different reanalyses can diverge in their depiction of rainfall and moisture transport. The authors may acknowledge the uncertainties inherent in their data and methods, such as how sensitive are the moisture convergence patterns to the choice of reanalysis or to errors in satellite precipitation? 

3. The manuscript examines many interacting processes, such as Atlantic inflow, the Congo Basin Cell, shifting heat lows, the Congo Air Boundary, AEJ-N/S jets, orographic uplift, etc. Is it possible to clearly distinguish the primary drivers of the rainy season onset from secondary or contextual factors? For instance, if low-level westerly inflow and subsequent mid-level moistening are the essential triggers, those should be highlighted as the key results. 

4. A few terms and conceptual elements would benefit from clearer definition, such as the shallow meridional overturning cell. Providing these definitions up front would make the physical interpretation clearer and help readers follow the proposed mechanism.

Please find my review attached.