The section addresses a relevant and very pertinent topic: the study of marine heatwaves in the Baltic Sea is extremely necessary. However, the section still requires more organization. The writing is often unclear. Important decisions were made for this section, although they still require support with the inclusion of more incisive justifications in the text. The section requires MINOR REVISIONS. Its current version cannot be approved for publication. To improve the manuscript, some questions are raised in the comments below, which can guide the authors.

General comments   

Why did the validation use only moorings (LT Kiel and Northern Baltic)? Are the analyses at two close stations (diamond and circle symbols in Fig. 2) representative for the entire Baltic Sea?

SST anomalies are computed with respect to a climatological SST considering the period 1997-2021, whereas MHWs are detected concerning the climatological data from 1993 to 2021. Why the choice of a dataset restricted to 1997-2021 for satellite SST? I suggest that the authors take a look at the link: https://data.marine.copernicus.eu/product/SST_BAL_SST_L4_REP_OBSERVATIONS_010_016/description

In section 2.4 “Model validation”, the author should describe the metrics and formulas applied to perform the analyses/study, and move Fig.1 and its description to a topic in section 3.

OSR8 guideline suggests a maximum of 5 figures. Confirm it!

Improve the writing in general. For instance, Section 3.2.2 shows interesting results that can increase the impact of the section, but are not described carefully and clearly. Review it!

English writing requires proofreading.

Specific comments 

(line 28) confirm the average period 1850-1900.  

(line 29) fifth or sixth? Replace with “among the 6 warmest years”  

(line 35) 1.35 K / 0.54^oC; use same unit 

(lines 51-70) Reduce the details to explain the satellite observations. Put their more relevant characteristics, then cite their main references in the text.  

(line 72) Remove “which are” 

(line 75) replace the first “and” with “to”.  

(line 96) replace “chapter” with “section” 

(lines 99-107) This part describes results that should not be present in the section 2 “Data and Methods” 

(lines 112-114) These lines describe results again. Organize the text and move them to the appropriate place.  

(line 116) The acronym MHWs is already mentioned in line 25. 

(lines 118-120) If the tools produce identical results, it is not relevant to mention the use of python and Matlab. Mention only “We use open-source tools to detect MHW (Oliver, 2016; Zhao and Marin, 2019)” 

(line 126) “the climatological data of 1993 to 2022”, replace “of” with “from”. Figure 5 says 1993-2021.

(line 131) This line is not clear.   

(lines 138-140) “Bothnian Sea”, “Bothnian Bay”, “Baltic Proper”, “Gulf of Finland” and “Gulf of Riga”. Find a way to specify/highlight these regions in one of the maps in Fig. 2.

(line 144) describe the metric “SST anomaly rank” in section 2.4 “Model validation”

(line 146) It would be better to avoid the mention of “obvious” here; replace it.

(lines 158-170) Specify the lat/lon points that delimiter the regions in discussion. The reading is difficult now.  

(lines 168-169) Would the Gulf of Bothnia include both the Bothnian Sea and Bothnian bay? Looking at Fig. 2, the highest SST anomalies are present in June and July in these regions. Why does the highest cumulative intensity derive from the temperature anomaly in November? 

(lines 169-170) Sentence is also not clear.

(lines 176-177) replace “after 2020” with “in the evaluated period”.

(line 181) Replace “rising mean temperatures”, my suggestion is “warming temperature trend”?

(lines 190-191) suggestion: replace “2018 was exceptional” with “In terms of total MHW days, the highest number is viewed in 2018”

(lines 203-204) “has a significant lower temperature of -0.3^oC to 4.5^oC as the climatological mean”, this sentence is not clear, since Fig. 3b shows only 2022. Improve the writing

(lines 208-209) “A few weeks prior to this MHW”, is the author referring to the extreme or severe MHW? Specify the time period. Improve the writing

(line 385) replace “chapter” with “section”.

(line 402) subplots 5g and 5h are not present

(Figure 3) change the color pallet

(Figure 5) line 402 states “The period used for the climatology is 1993-2021”, while line 126 says 1993-2022. In the end, what climatological period is used?

Improve the description of the caption in Fig. 5.

Please see attached PDF report. Overall it is an interesting report, specially the sections describing the vertical structure of MHW.

Some of the results and conclusions of the text need to be revised.