the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 23 Mar 2026
Brief communication: Extreme rainfall–driven flooding associated with the equatorial development of Tropical Cyclone Senyar in Aceh, Indonesia
Abstract. In late November 2025, extreme rainfall associated with the rare equatorial regeneration of Tropical Cyclone (TCs) Senyar triggered severe flooding across northern Sumatra, with Aceh Province experiencing the most severe impacts. Using satellite-based rainfall estimates from GPM IMERG, ERA5 reanalysis, and surface observations from BMKG, this brief communication provides a rapid hydrometeorological assessment of the event. Daily rainfall locally exceeded 400 mm on 25–26 November, concentrated over northern and eastern Aceh. Synoptic analysis indicates that, despite limited surface pressure deepening near the equator, persistent low-level moisture convergence and strong integrated vapor transport from the Malacca Strait, enhanced by orographic lifting along the Barisan Mountains, produced extreme rainfall and widespread flooding.
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Status: open (until 17 Jun 2026)
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CC1: 'Cyclone Senyar in Tropical athmosphere..', Muslim Amiren, 07 Apr 2026
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AC1: 'Reply on CC1', Saumi Syahreza, 07 Apr 2026
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We thank the commenter for this insightful question. We agree that the observed impacts do not fully resemble those of a mature tropical cyclone, as no clear eye or symmetric circulation was present. As noted in the manuscript, the system exhibited asymmetric circulation and lacked a well-defined inner core. It is therefore better interpreted as a developing or marginal cyclonic disturbance in a near-equatorial environment. Nevertheless, persistent convection and strong moisture convergence produced extreme rainfall and flooding. We will revise the manuscript to better clarify this distinction. Thank you again for this valuable comment.
Citation: https://doi.org/10.5194/egusphere-2026-694-AC1 -
AC2: 'Additional clarification on system structure', Saumi Syahreza, 08 Apr 2026
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We would like to further clarify that the system was not entirely asymmetric. As described in the manuscript, it exhibited a partially organized structure with noticeable asymmetry, rather than a fully developed symmetric cyclone. We will revise the manuscript to better clarify this distinction.
Citation: https://doi.org/10.5194/egusphere-2026-694-AC2
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AC2: 'Additional clarification on system structure', Saumi Syahreza, 08 Apr 2026
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AC1: 'Reply on CC1', Saumi Syahreza, 07 Apr 2026
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RC1: 'Comment on egusphere-2026-694', Anonymous Referee #1, 09 Jun 2026
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Overall, the concept of this study is quite straightforward and sound. However, the gaps and novelties revealed are not yet clear, aside from the fact that it is a recent case study.
The Vamei (2001) system case also warrants comparison in the analysis and background, given the cyclonic system that passed through Sumatra and its proximity to the equator. Other studies of flooding and cyclonic events in the study area also need to be discussed.
Introduction. Line 35 needs to add a reference for the first sentence. There is a duplication in line 59, the discussion of the BMKG data explained in the previous paragraph. There is a typo in line 66.
Again, gaps and novelties are not emphasized enough in the background and need to be explained in more detail.
Data and Method. References for each data and method should be given more attention and added, such as ERA5 data (Hersbach et al., 2020) and other data/methods used.
Result
Figure 1. The position of Senyar in each phase needs to be clarified with markings to better understand the dynamic conditions displayed. In the wakening phase, there is a system in the South China Sea. Is that also Senyar? If not, there will be confusion.
The use of a blue, white, red (or other) color bar would be more appropriate for anomaly values (negative-positive). An anomaly value can also illustrate the deviation and its significance relative to climate conditions.
Need to add the units and representative value of the wind vector in Figure 1.
The preprint contains strange and confusing boxes. Are they MSLP? Is this oddity unique to the preprint version, or is there an error in the display?
The image caption could be shortened.
Figures 2 and 3, especially 2 (a) and 3(c). Do those figures show the same observation data? What is different? If those are the same, then no duplication is needed.
The color bar in Figure 3 does not accurately represent the contrast in rainfall. Values below 0 or below 1 can be shown in white. And choosing a different color bar with better contrast is suggested (see Figure 2).
The discussion of the GPM data in section 3.2 is not clearly necessary, as the subsequent discussion uses only observational data. Thus, section 3.2 loses the point and aim of the discussion. Do we still need this section?
In-depth discussion option. Based on your analysis, rainfall remains after the peak of extreme rainfall. So, is all rainfall truly related to the Senyar system? Or there is a convective system along with that. Can you divine the rainfall of Senyar or the convective system?
The analysis of the flood sequence in discussion 3.4 and Figure 4 is very interesting and provides a key insight into the occurrence of severe flooding. But why does Figure 4 only show data from 25-26? And why not the entire pre- to post-Senyar sequences?
There are many questions and discussions that could be explored and explored, such as:
How did inundation change from day to day throughout the Senyar episode compared to rainfall at the same time? How did the location of rainfall and peak rainfall correspond to the location of inundation? Why did inundation/flooding occur so massively?
Adding data on land cover and the impact of settlements would further refine the analysis of the direct impacts and vulnerability of this region.
Citation: https://doi.org/10.5194/egusphere-2026-694-RC1
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It is very interesting to know more about Cyclone Senyar. Why does it occur in Tropical nature background. I saw, there is no actually cyclone, but only a huge flooding. Could we still say a cyclone senyar, or other name to call? Would you please you explane how is it different in characteristic of a Tropical Senyar cyclone?
Thanks so much,
Muslim Amiren