The previous summer wave height record dates back to July 2007, when a gauge operated by the Finnish Meteorological Institute registered a significant wave height of 3.7 meters.

This time, the exceptional wave activity was caused by a west-northwest gale driven by Cyclone Ulla. Wind speeds in the central and western Gulf of Finland reached up to 27.1 meters per second in gusts. While this sets a new summer record, it falls short of the Gulf of Finland's all-time record. The highest significant wave height — approximately 5.8 meters — was measured by LainePoiss in October 2023.

Such high waves require rather specific conditions. "Generally speaking, to reach a significant wave height of four meters in the Gulf of Finland, you need wind speeds of at least 18 meters per second sustained for six hours, with the wind direction not deviating from the gulf's main axis by more than a few dozen degrees," explained Victor Alari, senior researcher at TalTech. The greater the angle between the wind direction and the gulf's axis, the stronger the wind needs to be to generate similar wave conditions.

Monitoring network in need of updating

According to the Estonian Environment Agency's weather service, wind gusts at Vaindloo reached up to 30.0 meters per second. Although record wave readings were taken near Naissaar, wave heights in the eastern Gulf of Finland may have been even higher. "The wind pattern overnight was such that waves were likely larger in the eastern Gulf than in the central part. This is indirectly supported by the fact that wind conditions were more severe to the east," said Victor Alari.

This, he noted, highlights the shortcomings of the current monitoring network. "It shows how important monitoring coverage really is. Right now, we lack wave measurements in the eastern Gulf of Finland and, in that respect, we're essentially blind," the senior researcher said.

According to Alari, forecasts from both the Environment Agency and the Copernicus Marine Service are generally very accurate and improve further as weather events approach. However, the absence of direct measurement data makes it more difficult to assess conditions and refine models.

To improve situational awareness, the monitoring network should be expanded. "For the Gulf of Finland, an optimal offshore wave monitoring setup would have measuring stations roughly every 100 kilometers — for example, one near Osmussaar, the current one at Naissaar and an additional one near Vaindloo. That would give us a reasonably clear picture of wave conditions across the Gulf," Alari explained.

Better safe than sorry...

Victor Alari pointed out that when it comes to waves, height alone isn't what matters — their length plays a critical role as well. "The peak wave period overnight was about nine seconds, which means the wavelength was roughly 130 meters. So it's no surprise that even the departures of some large ships were canceled. It's not just wave height that causes vessels to pitch and roll — wavelength and the angle between a ship's course and the wave direction are also key factors," the senior researcher explained.

At the same time, the maximum wave height can be up to twice the significant wave height. Mariners should keep this in mind and pay attention to it when reviewing marine forecasts. One should never go to sea in conditions that exceed a vessel's technical specifications.

For example, in the case of rowboats and smaller vessels, the wave height limit is typically just 0.5 meters. "If you see a forecast predicting a significant wave height of 0.3 meters, you should already avoid going out to sea, because the maximum wave is likely to reach 0.5 meters," Alari illustrated.

"In addition, although today's storm occurred in summer, it happened during a relatively dark part of the night. That makes it difficult to see the direction of the waves. On open water, the operator of a small boat must always keep the bow facing into the waves and adjust course within seconds," Alari added.

--

Follow ERR News on Facebook, Bluesky and X and never miss an update!