A record low sea level of -153 cm, 34 cm below the previous minimum, was measured in the Bothnian Bay in November 2024. This extreme event was caused by a strong and long-lasting windstorm that followed an unusual track. The BAL MFC NRT physical forecast system was able to accurately predict this sea level 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.

We studied annual maximum sea levels in the Finnish coastal region. Our aim was to better quantify the uncertainty in them compared to previous studies. Using four statistical models, we found out that hierarchical models, which shared information on sea-level extremes across Finnish tide gauges, had lower uncertainty in their results in comparison with tide-gauge-specific fits. These models also suggested that the shape of the distribution for extreme sea levels is similar on the Finnish coast.

We analysed the correlation of sea level and wind waves at a coastal location in the Gulf of Finland using tide gauge data, wave measurements, and wave simulations. The correlation was positive for southwesterly winds and negative for northeasterly winds. Probabilities of high total water levels (sea level + wave crest) are underestimated if sea level and waves are considered independent. Suitably chosen copula functions can account for the dependence.

A natural hazard is a naturally occurring extreme event with a negative effect on people, society, or the environment; major events in the study area include wind storms, extreme waves, high and low sea level, ice ridging, heavy precipitation, sea-effect snowfall, river floods, heat waves, ice seasons, and drought. In the future, an increase in sea level, extreme precipitation, heat waves, and phytoplankton blooms is expected, and a decrease in cold spells and severe ice winters is anticipated.

Using sea level and precipitation observations, we analysed the meteorological characteristics of days when heavy precipitation and high sea level occur simultaneously in Finland. We found that around 5 % of all heavy precipitation and high sea level events on the Finnish coast are so called compound events when they both occur simultaneously, and these events were associated with close passages of mid-latitude cyclones. Our results act as a basis for compound flooding research in Finland.