Record low sea levels in the Bothnian Bay in November 2024

Tuomi, Laura; Johansson, Milla M.; Twelves, Andrew; Rantanen, Mika; Lagemaa, Priidik; Kanarik, Hedi; Särkkä, Jani; Raudsepp, Urmas; Westerlund, Antti

doi:10.5194/sp-7-osr10-16-2026

Articles | Volume 7-osr10

https://doi.org/10.5194/sp-7-osr10-16-2026

© Author(s) 2026. This work is distributed under
the Creative Commons Attribution 4.0 License.

Report:

10th edition of the Copernicus Ocean State Report (OSR10)

https://doi.org/10.5194/sp-7-osr10-16-2026

© Author(s) 2026. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 7-osr10

30 Sep 2026

| OSR10 | Chapter 4.2

| 30 Sep 2026 | OSR10 | Chapter 4.2

Record low sea levels in the Bothnian Bay in November 2024

Laura Tuomi, Milla M. Johansson, Andrew Twelves, Mika Rantanen, Priidik Lagemaa, Hedi Kanarik, Jani Särkkä, Urmas Raudsepp, and Antti Westerlund

Data sets

Baltic Sea Physics Analysis and Forecast EU Copernicus Marine Service Product https://doi.org/10.48670/moi-00010

Baltic Sea - In Situ Near Real Time Observations EU Copernicus Marine Service Product https://doi.org/10.48670/moi-00032

Weather and Sea level Real-time observations FMI https://en.ilmatieteenlaitos.fi/download-observations

ERA5 monthly averaged data on single levels from 1940 to present Hans Hersbach et al. https://doi.org/10.24381/cds.f17050d7

Sea level observations from Swedish Meteorological and Hydrological Institute and Swedish Maritime Administration SMHI https://www.smhi.se/data/hav-och-havsmiljo/havsvattenstand/

Short summary

A record low sea level of −153 cm, 34 cm below the previous minimum, was measured in the Bothnian Bay on 21 November 2024. This extreme event was caused by a strong and long-lasting windstorm that followed an unusual track. The Copernicus Marine Service Baltic Sea forecast system accurately predicted the event 3–4 days in advance. However, forecasts with longer lead times failed to predict the record low sea level, although they did indicate a significant drop in sea levels during the storm.