Summary:

Using station-based and reanalysis data, this authors present a valuable analysis of the unprecedented November 2023 Rio de Janeiro heatwave, highlighting the driving effect of atmospheric blocking and its linkage to the El Nino event. They also discuss the role of soil moisture deficits associated with the heat extreme event. Finally, they extend the analysis to future projection and find that the frequency of heat extremes is expected to increase in the future. The paper is well-written and present clear results. However, the physical driving mechanism analyses could be further strengthened by quantifying the relative roles of blocking and soil moisture decline in driving the heat extremes. Moreover, the robustness of the linkage between the atmospheric blocking and ENSO needs to be further clarified. I thus recommend a major revision by addressing the following comments.

Specific comments:

1, One major goal of this study is to figure out the physical drivers of the November 2023 heatwaves. I would like to recommend the authors to perform a thermal budget analysis, which would be helpful to understand the relative contributions of atmospheric circulation and diabatic heating that is mainly influenced by the surface heat fluxes and soil moisture.

2, In the abstract, the authors claim the atmospheric blocking is affected by the El Nino, but they did not provide sufficient evidence for this in the historical analysis. Particularly, they only show the historical correlation between Nino 3.4 index and number of days in heat extreme. I would like to suggest to perform the circulation composite in the spring of El Nino years.

Dear Authors, 

please refer to the attached PDF for my review of your manuscript.