A storm surge is expected along the German Baltic Sea coast from this evening (Saturday, 17 October 2026). The Federal Maritime and Hydrographic Agency (BSH) The highest water levels are expected during the night leading into Sunday and during the day on Sunday. At the same time, the wind may pick up. For boats in the harbour, this means a double challenge: rising water levels and additional forces caused by the wind and the movement of the water.
However, the forecast is still subject to considerable uncertainty. Predictions for individual ports may therefore still vary significantly from one another.
These water levels are expected
The BSH currently lists the following areas for the night from Saturday to Sunday:
- Lübeck Bay: 0.65 to 1.30 metres above mean sea level (MSL)
- Kiel Bay: 0.40 to 1.20 metres above mean sea level
- West of Rügen: 0.60 to 1.05 metres above mean sea level
- East of Rügen: 0.60 to 1.10 metres above mean sea level
- Small lagoon: 0.50 to 0.75 metres above mean sea level
The figures are based on Normal Sea Level (NSL). Along the German Baltic Sea coast, NSL corresponds to chart datum – that is, the reference level for depth measurements on nautical charts. A water level of one metre above NSL therefore means, in mathematical terms, one metre more water above the depth shown on the chart.
The forecasts describe regional areas and time periods, not necessarily the highest water level at every single port. For boat owners, therefore, the situation at their own mooring is crucial. The Flood and Storm Surge Information for Schleswig-Holstein It brings together continuously updated warnings and water level data.
No all-clear yet despite low water levels
In Flensburg, the water level on Saturday afternoon was provisional data at around 0.44 metres above mean sea level. This reading reflects the current situation – not the expected water levels overnight and on Sunday. A low water level in the morning is therefore no cause for complacency.
Precautionary measures have already been announced in the city. According to Information from the NDR Residents living near the harbour are to be able to collect sandbags free of charge on the Exe on Saturday between 12 noon and 5 pm. This is a precautionary measure in anticipation of the expected situation and does not indicate that flooding has already occurred.
There are also various model predictions available for Flensburg. Whilst the BSH forecasts a level of around 1.08 metres for Sunday lunchtime, Danish calculations put the figure at around 1.64 metres for Sunday morning. These figures are derived from various forecasting models and cannot be readily compared with one another.
Gusts of wind can increase the strain
Following the Warning Bulletin from the German Weather Service Winds over the Baltic Sea will pick up from Saturday afternoon. During the night leading into Sunday and on Sunday morning, isolated gusts of around 80 kilometres per hour – nine on the Beaufort scale – are possible. The wind will gradually veer north-east to east and is not expected to ease off again until the night leading into Monday.
As far as mooring safety in the harbour is concerned, this means that not only is the water level rising, but the strain on ropes, cleats and jetties is also increasing.
The yacht must be able to rise with the water
The most important rule when the water level rises is: Don’t simply pull the mooring lines as tight as possible. Mooring lines that are too short exert strong downward forces during high water and can prevent the yacht from floating with the water.
However, the mooring lines must not be too loose either. Otherwise, the boat may bang against the jetty or neighbouring yachts. The key is to route the lines in such a way that they allow freedom of movement upwards whilst at the same time restricting movement in the longitudinal direction.
This should be checked whilst the vessel is moored
- Adjusting the mooring lines: The lines must be long enough to allow the yacht to rise with the water. Long, counter-running spring lines restrict movement in the longitudinal direction.
- Distributing the load: Distribute additional mooring lines amongst several suitable cleats and attachment points. No single cleat should bear the entire load.
- Ensure adjustability: Choose the arrangement so that individual lines can be adjusted without having to loosen the others.
- Check for signs of wear: Check the gunwales, edges and dolphins, and fit suitable chafing protection. Replace damaged mooring lines; old sheets or halyards are not suitable replacements.
- Securing ropes to bollards: Secure the mooring line to prevent it from slipping. A simple loop tied only around itself may come loose when the tension is released. With suitable bollards, a more reliable method of securing the line is recommended, such as a stopper knot with two half-hitches. The line must nevertheless remain long enough to allow the yacht to rise with the water.
- Check the height of the dolphins: Even a secured rope won’t help if the dolphin is too low for the expected water level.
- Positioning the fenders correctly: Fit fenders at the points of contact that are actually at risk. As the water level rises, the position of the hull relative to the jetty changes.
- Reducing the wind resistance area: Remove the bimini, the galley hood and, if necessary, the sprayhood. Stow away loose equipment, close the hatches and, if strong winds are forecast, lower the furling sails as early as possible.
- Securing the electrical system: Charge the batteries, then disconnect the shore power cable and stow it away safely. Do not touch any electrical equipment that is already submerged.
Shock absorbers can reduce load peaks, but they do not replace the necessary freedom of movement of the mooring lines.
Work on the boat should only be carried out whilst access to the mooring is safe. Flooded jetties, closed-off harbour areas or already hazardous wind and wave conditions are not the place for belated attempts to secure the boat. The instructions of the harbour master and the emergency services take precedence.
Anyone who is unable to be on site should contact the harbour master or a trusted person at the mooring now. Moving to a more sheltered mooring is only an option if done in good time, in safe conditions and in consultation with the harbour authorities. If the weather is already dangerous, setting sail is not a one-size-fits-all solution.
Storm surge warning shortly before the 2023 anniversary
The latest warning has reached the Baltic Sea coast just a few days before the third anniversary of the the severe storm surge of 20 and 21 October 2023. At that time, 48 yachts sank in the harbour of Schilksee alone, and numerous jetties were severely damaged.
However, the fact that these events occurred in close succession does not mean that a similar event is imminent. The current regional BSH forecasts do not allow for a direct comparison with the storm surge disaster of 2023. The key lesson Nevertheless, the following advice remains relevant: keep an eye on warnings at an early stage, prepare your mooring in good time, and do not wait until the jetties are already flooded.
What measures to prevent storm surges have been implemented in your home port since October 2023?
Ursula Meer
Redakteurin Panorama und Reise