Summary: The manuscript presents a characterisation of an extreme low sea level in the Gulf of Bosnia in the Baltic Sea. The magnitude of this extreme was exceptional compared to the past historical record. This extreme event was linked to winds flowing from a specific direction. The study estimated the return period of this extreme and assessed the short-term forecast for it.

Recommendation: The manuscript is clearly written, and the analysis is, in my opinion, correctly conducted. I have, however, some concerns about the suitability of the topic for the journal, a decision that the editor or the editorial board should make. The manuscript presents an analysis of a very specific sea-level extreme. This assessment may certainly be relevant from the operational meteorological or oceanographic point of view, but I do not clearly see its impact as an assessment report for 'State of the Planet'

Leaving this question aside, I have a few suggestions that the authors may want to consider:

1) The abstract indicates some sea-level figures to characterise the magnitude of the extreme, but these are only meaningful to researchers working specifically in this geographical area. Also, it would be more useful to indicate the magnitude in terms of standard deviations derived from some climatological period (possibly detrended to subtract the impact of the GIA)

2) The Abstract should also mention the exact date of the extreme. This is first mentioned at the end of the introduction.

3) line 96 'We present winds measured at Kalajoki...' daily, hourly, 6-hourly..?

4) The resolution of Figure 1 should be improved.

5) line 170 'forecast lengths'

I think the authors mean forecast horizons. For instance, the length of a forecast be 10 days if it s continued beyond the forecast horizon of , say 1 24 hours.

6) The GEV analysis is correctly conducted using detrended data. It is interesting to know whether November 21th remains a record sea level even in the detrended series

7) A GEV analysis of the winds, for instance, daily means, would also be interesting. It would address the question of whether the sea-level record was due solely to the magnitude of the winds, or to some combination of strong winds, the prefilling state, or sea-ice cover.

8) What were the sea-ice cover conditions? Ice cover is known to modulate the amount of momentum transferred from the atmosphere to the ocean. Did a smaller-than-normal ice cover play a role? Somewhat surprisingly, ice cover is not mentioned at all in the manuscript (or I missed it). This would increase the 'climatological aspect' of the study and perhaps make it more suitable for publication in State of the Planet

This paper explores the accuracy of the Finnish Baltic Sea Monitoring and Forecasting Centre native model (named NRT physical system) in reproducing observed sea levels during a severe windstorm in November 2024. Model sea surface heights are compared against nearby tide gauge observations.

The manuscript assesses the NRT physical system model accuracy under different forecasting lead times (12-24 hrs / 36-48 hrs/ 60-72 hrs  & 84-96 hrs), with the shortest lead times providing higher forecast accuracy.  The authors found that the model tends to underestimate highs, and lows, thus not fully reproducing the extremes, particularly in the longer range forecasts. This is a known limitation of this version of the model, from prior literature.

With the negative storm surge being recorded in high resolution by the tide gauges, the return period of this record-breaking sea level low is estimated, using measurements from Kemi tide gauge (in the context of the longer 1977-2024 record). Land uplift and sea level changes over the period are known and were used to detrend the data. Return period estimates are demonstrably more accurate if observed extremes, like this storm, are included in the analysis.

General comments and scientific issues:

This manuscript describing the modelling of a uniquely severe storm at the northern extremity of the Baltic Sea, in the Bothnian Bay and Gulf of Finland in November 2024, reads as a technical report of the event - the purpose of which is validating the Baltic Monitoring and Forecasting Center’s Near Real Time model for extreme events.

The topic of representing extreme sea levels due to storms should be of great interest for modellers, and is a topic of current interest in our changing climate. The goals of the paper are neatly set out and indeed addressed. The methodology and results are clear and well presented, although Table 1 may require some improvements to the headers, and description, for clarity (e.g. CMEMS is not defined in the report. The Product ID & Type descriptions are a little confusing). Also the role of the Automatic Weather Stations (lines 95-103) in the procedure may need clarifying. Data appears to be accessible for experiments to be reproduced. Results do certainly support the interpretations and conclusions. The entire manuscript is well structured and findings are concisely presented. As such it is a nice read.

However, the authors may wish to consider posing a scientific question or hypothesis to elevate the motivation of this manuscript for the readership. The innovation, or novelty, or new conclusions, presented by this paper was not clearly stated. I imagine few extreme negative storm surges are captured for model calibration and development, therefore a discussion of why the model had difficulty, and the things that could be considered to improve the model to better represent and forecast such events (even to longer lead times) would be an interesting contribution to the scientific knowledge. As such, it may benefit the manuscript if the discussion and conclusions sections are reworked to provide new insights, or discuss the unique problems of modelling such extreme events, alongside the unique tide gauge observation data and unique storm event.

There are a number of abbreviations and initialisms presented in the report, and as such, it may also be beneficial to consider an end of report Glossary for reference.