A Baltic July: warmth near the seasonal norm, fickle water, and squalls the real worry for sailors

This July on the Polish coast is shaping up to be a typical seaside summer: no exceptional heat, but plenty of variability. We have pulled together the latest long-range forecasts from IMGW and the long-term climate norms for the whole coastline, from Pomeranian Bay to the Vistula Lagoon, with Daily Mare meteorologist Mariusz Jasłowski explaining what to watch for when planning a holiday or a passage.

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23 june 2026   |   09:43   |   Source: Gazeta Morska   |   Prepared by: Kamil Kusier   |   Print

fot. Mariusz Jasłowski / meteo24.com.pl

The season in brief: warmer, but mainly in the south

The experimental long-range forecast from the Institute of Meteorology and Water Management (IMGW) points to a summer above the 1991–2020 norm across Poland. For the coast, though, the most recent updates add nuance. The clearer positive temperature anomaly is concentrated in the south of the country, while in the north July should run close to the long-term average. In other words, the coastal belt is closer to the norm than to the front of any heatwave. July rainfall should also fall within the norm, although this summer's character is billed as dynamic, with hot, stormy and briefly cooler spells alternating.

- Treat long-range forecasts as a signpost, not a timetable, says Daily Mare meteorologist Mariusz Jasłowski. - For the coast, the latest charts do not promise exceptional heat. The stronger anomaly sits in the south of the country, while up here in the north July looks close to the long-term norm. That is a typical situation for the coastal belt, and good news for anyone who copes badly with heat.

Jasłowski also tempers hopes for a single, predictable scenario across the whole month.

- A seaside July is not one pattern but a sequence of episodes: a few hot days, then a front comes through, thunderstorms, a short cool spell, and high pressure again. You have to be ready for variability, not for a steady heatwave from the first of the month to the last.

The thermometer along the coast: from Szczecin to the Vistula Spit

July is not the same all along the coast. The most continental point is Szczecin, set inland on the Oder. This is where it gets warmest during inflows of hot air, with average highs of around 23–24°C and as much as 28–32°C in a heatwave, along with warmer nights and less of the sea's moderating influence.

Świnoujście and the whole western open coast already follow the rules of maritime convection: highs usually 21–23°C, an afternoon sea breeze and milder conditions than inland. It is much the same on the open Pomeranian shore around Łeba, Władysławowo and the seaward side of Hel, where exposure to the wind is greater.

The Tricity sits on the sheltered Gulf of Gdańsk. In calm, sunny spells the shallow inshore waters off Sopot and Gdańsk can warm pleasantly, and the air tends to be warmer than on the open coast. At the eastern end, by the border with the Kaliningrad Oblast, Krynica Morska and the Vistula Spit resemble the rest of the open coast on their seaward side, but right alongside lies the Vistula Lagoon, a shallow body of water that heats quickly and often holds the warmest water on the entire coast.

The common denominator for the whole belt: highs most often 21–24°C, but both cool maritime days around 18°C and hot inflows above 28–30°C are realistic. July is also one of the wettest months of the year, with rain mostly in showers and thunderstorms, and plenty of sunshine between storms under very long days.

The water, the great unknown

For beachgoers and swimmers it is the water temperature, not the air, that is often July's biggest disappointment. The open Baltic usually sits at 17–20°C this month, while sheltered, shallow waters such as the Vistula Lagoon can manage more. The catch is that on the Polish coast the water is a lottery, because of upwelling.

The mechanism is simple. When an offshore wind, most often from the north-east, persists for a few days, the warm surface layer is pushed out to sea and cold water rises from the depths. The effect can be abrupt.

- The most common disappointment for holidaymakers is the water, Jasłowski says. - A few days of offshore wind is enough to push the warm layer away, and cold water rises from below. The temperature can drop from twenty to the low teens, sometimes ten degrees, within a day, mainly on the open coast from Hel to Łeba. The Gulf of Gdańsk and the Vistula Lagoon react to it far less. And no monthly forecast will predict that, it is decided a few days ahead.

Wind, sea breeze and waves: the weather that matters to sailors

For a sailor on the Baltic, what matters most in July is not the temperature but the wind, the sea state and the storms. Statistically, July is among the lightest-wind months of the season, with a predominance of westerly and north-westerly directions and a force most often in the 2–4 Bft range. On settled, fair days it is mainly the thermal that drives the wind on the water.

- On fair days it is mostly the sea breeze that does the work, Jasłowski explains. - The sea breeze sets in around midday, builds through the late afternoon and dies away in the evening, while at night there is a weaker land breeze. On Puck Bay you can build a whole afternoon's sailing on it. But when a low or a front comes through, the gradient wind can add to it and back or veer, and then you have a genuine Force 5 or 6, locally more.

The biggest hazard of July, however, remains thunderstorms. This is the peak of the convective season, and storm cells most often form in the afternoon and evening, frequently over land, before moving out over the water along a squall line.

- What keeps a sailor awake in July is not the temperature, it is the storms, stresses the Daily Mare meteorologist. - A squall line means a sudden shift and jump in the wind. Gusts can exceed seventy kilometres an hour, with hail on top. The rule is simple: reef early, watch the radar and do not underestimate building cumulonimbus, especially on the lagoons, where shelter can be a long way off.

Then there is the sea state and visibility. On the open Baltic and Pomeranian Bay the wind sea is short and steep, building quickly in an onshore wind. The inland waters, Puck Bay, the Szczecin Lagoon and the Vistula Lagoon, range from flat to a tiring short chop in a fresher breeze. Fog is rarer in July than in spring, but possible, especially when warm air moves over cold water pushed up by upwelling. The compensation is a very long day: at this time of year first light comes around half past four and dusk falls after nine, opening a wide window on the water.

The waters from west to east

Around the Szczecin Lagoon and the Oder, sailors have a sheltered area, but one prone to thermal and gusty winds near the shore and to thunderstorms. Świnoujście and Pomeranian Bay are the gateway to the open Baltic, more exposed to swell and to north-westerly wind. The open Pomeranian shore, from Łeba through Władysławowo to the seaward side of Hel, means the full Baltic, sea breeze and swell, and so the most space and at the same time the most exposure.

The heart of Polish sailing and windsurfing remains Puck Bay and the Gulf of Gdańsk. Puck Bay is shallow and sheltered, with even water and fairly predictable thermals, from Rewa through Puck to Jastarnia and the inner side of Hel. At the eastern end, the Vistula Lagoon tempts with a sheltered, shallow area, a short, steep wave in the wind and access from the Baltic through the canal across the Vistula Spit. It is worth remembering that a state border divides the lagoon, and navigation restrictions apply in the border zone.

What to watch and how to plan

A seasonal tendency is not enough to put to sea. The closer to the date, the more precise the forecast, so a decision on a passage is best based on current data. Useful sources are IMGW's storm warnings and bulletins for the Baltic, the ICM model on meteo.pl, services such as Windy or PredictWind, and on the spot a word from the marina or harbourmaster.

- The closer to departure, the better we know the wind and the waves, Mariusz Jasłowski concludes. - Three or four days out, they can be forecast with reasonable accuracy. So when planning July, look at the tendency, but base the decision to put to sea on current bulletins and warnings. The sea forgives less than a long-range forecast does.

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