Which wind forecast works on the water?

The forecast says 7 m/s, but on the water the wind feels either much stronger or dies away before you are done. This guide explains to kitesurfers, wingfoilers, windsurfers and boaters what the number means, which forecast is worth checking when, and where people often go wrong.

What the wind figure means

In Finnish forecasts and observations, the wind is the 10-minute mean wind at a height of 10 metres. The wind at any given moment can be noticeably stronger.

A gust is a strengthening of the wind that lasts a few seconds. At sea, gusts are typically about 20–30% stronger than the mean wind. When the wind comes over land, the difference grows, and gusts can be more than 50% stronger than the mean wind. That is why an 8 m/s wind from the land feels much more unsettled on the water than an 8 m/s wind from the sea.

Wind direction tells you where the wind is coming from: a southerly wind blows from the south. For your sport, what matters most is the direction relative to the shore:

• Wind from the sea towards the shore (onshore) brings you back to the shore if something goes wrong.
• Wind blowing along the shore (cross-shore) is the easiest for many sports: you can go out and come back the same way.
• Wind from the land out to sea (offshore) carries you and your kit away from the shore, and it is gustier. Beginners should not go out on the water in a wind that blows away from the shore.

The most common mistakes

• Checking the city weather. A city forecast describes the wind in the town centre. At sea it is usually windier.
• Looking only at the mean wind. You reach the limits of your kit and your own skills in the gusts, not in the mean wind.
• Not noticing the wind direction relative to the shore. The same 8 m/s is a completely different wind from the sea than from the land.
• Trusting an old forecast. Forecasts are updated several times a day. Last night's forecast may already be different by the morning.
• Trusting a single figure a week ahead. Wind direction and strength can usually be forecast 2–5 days ahead. Beyond that, a forecast gives only an overall picture.
• Forgetting about the return. The wind can turn and strengthen during the day. Also check what wind is expected for when you plan to come back.
• Expecting the morning wind to last. On a sunny summer day, the sea breeze can change the wind direction and strength in the afternoon. More on this below.

Which forecast to check when

Warnings and the marine forecast

The weather forecast for shipping (Säätiedotus merenkulkijoille) from the Finnish Meteorological Institute (FMI, Ilmatieteen laitos) gives the wind direction and speed for the next 24 hours for each sea area, such as the western Gulf of Finland or the Archipelago Sea (Saaristomeri). It is made above all for the open sea. A wind warning for a sea area gives the strongest mean wind forecast at sea during the 24-hour period. Close to the coast the wind may be lighter, but do not count on it. Nor does the absence of a warning mean that conditions are suitable for a beginner.

Detailed and coarse models

All wind forecasts are based on weather models that calculate the wind on a grid. The most important ones for Finnish waters are HARMONIE, run jointly by the Nordic weather services, which has a 2.5 km grid and reaches about two and a half days ahead, and ECMWF, from the European Centre for Medium-Range Weather Forecasts, which has a grid of about 9 km and reaches more than ten days ahead. A small bay or headland does not show up in either model, and even less in the coarse one. VamoSpot shows both, and you can switch model in the Layers menu. How the models calculate a forecast, and why the same model updates in different services at different times, is explained in the guide How are weather forecasts made?

If different weather services show markedly different figures for the same day, the situation is uncertain. In that case, prepare for the strongest forecast and keep an eye on the wind gauge.

The forecast and the wind gauge

The model's figure is an average over the whole grid box. A wind gauge measures at a single point, and its reading is affected by location, height and surroundings: even a single tree or building creates eddies. That is why a gauge can show a different figure from the sea area next to it.

The gauge tells you what is happening now, and the forecast tells you where things are heading. Check how recent both are: in VamoSpot, the forecast's update time is shown in the Layers menu and the gauge reading on the spot card. When there is a wind gauge near a spot, VamoSpot corrects the spot's forecast for the next few hours according to the gauge reading, and the card also shows the gauge's gust. More on this in the guide Spot settings.

Checklist before you go

• Are any wind warnings in force for the sea area?
• What do the marine forecast and the detailed model say about wind direction and strength?
• How strong are the gusts? Compare them, not the mean wind, with your own skills and kit.
• Where is the wind coming from relative to the shore? If it blows away from the shore, give it a miss.
• Are thundery showers or poor visibility forecast? A thundery shower can bring sudden, strong gusts, even if the wind was light before it.
• What wind is expected for when you plan to come back?
• Is the day sunny with a light wind? Be ready for a sea breeze in the afternoon.
• What does the nearest wind gauge show now, and does it match the forecast?
• How cold are the water and the air? In cold water your strength runs out quickly, so your kit and your distance from the shore need to match.
• Tell someone where you are going and when you will be back. Do not go out alone if you are a beginner.
• If in doubt, give it a miss. Keep watching the weather while you are on the water too: on wide open stretches of water and in exposed areas, the wind can pick up quickly.

Example days

A sunny day in June, light northerly wind forecast over the Gulf of Finland

A typical sea-breeze day. In the morning there is a light wind from the land. A few hours after sunrise, the wind can turn to blow from the sea and strengthen towards the afternoon. There may still be a calm zone just off the shore, even though it is windy further out at sea. Do not go further out looking for wind: you may not be able to get back to the shore from beyond the calm zone. In the evening the wind eases and goes back to the north.

A sunny day, moderate wind at an angle from the land

The sea breeze and the background wind can reinforce each other, and the afternoon wind may be stronger than in the morning. Keep an eye on the wind gauge if your kite or sail is already at its upper limit in the morning wind.

A sunny day, fresh wind from the land

The sea breeze develops late or not at all, and if it does develop, it may stay out at sea. At the shore the wind blows away from the shore and is gusty after crossing the land. This is not a day for beginners.

A cloudy day, a low-pressure system bringing a south-westerly wind

No sea breeze develops, because the sun does not heat the land. The wind is background wind, and the forecast describes it well. Follow the warnings and the timing of the front, and be prepared for gusty wind after a cold front.

The sea breeze is not just any wind from the sea

The wind in a forecast is the background wind: the wind of low- and high-pressure systems, which blows by night and by day. The sea breeze is something different. It is a local wind that the sun creates on the coast during the day. The sun heats the land faster than the sea, warm air rises over the land, and cool air flows in from the sea to take its place.

When it happens and what it is like

• Sea breezes occur especially in spring and early summer, when the sea is still cold. A sea breeze needs an almost clear day and a light or moderate background wind.
• It starts a few hours after sunrise, strengthens towards the afternoon and gradually turns clockwise. In the evening it eases, and the wind returns to the direction of the background wind.
• A sea breeze on its own is often light. In a model representing a coastline like Helsinki's, it was about 4.5 m/s with no background wind, but with a suitable background wind of 4–7 m/s the wind on the coast strengthened to 7.5–9.5 m/s (Gahmberg et al. 2010).

What the background wind does to the sea breeze

Imagine you are standing on the shore, facing the sea.

For example, in Helsinki on 11 September 2002, the wind at Isosaari, an island 8 km from the shore, turned south-westerly in the afternoon and blew at 5 m/s, but at Kaisaniemi in central Helsinki the wind blew from the north all day (Gahmberg et al. 2010). So the wind at the shore can be blowing from the land even though a sea breeze is blowing a few kilometres away.

Threshold values vary between studies. According to a review by Crosman and Horel (2010), a wind of 4–8 m/s from the land can hold the sea breeze back at the coastline, and with a wind of more than 6–11 m/s no sea breeze develops at all.

Sea-breeze fronts and weather fronts

Where the sea breeze meets the warm air over the land, the air rises and cumulus clouds form. In the afternoon these can turn into showers. A weather front is something different: it brings cloud and changes the background wind. Because the sea breeze needs sunshine, a sea breeze does not usually develop on a cloudy day when a front is passing.

Wind strength: Finnish terms, Beaufort and knots

Abroad, in sailing and in many equipment guides, wind is given in Beaufort or in knots. The scales do not line up exactly, but roughly they correspond like this:

Rule of thumb: one metre per second is about two knots. In Finland, wind warnings for sea areas are based on the mean wind: yellow 14–20 m/s, orange 21–32 m/s and red over 32 m/s. The threshold for a storm varies from country to country, and in the United States, for example, the mean wind is calculated over a shorter period, so the same wind gives a higher figure. With a foreign forecast, it is therefore worth checking the unit and what the figure actually means.

Is AI making forecasts more accurate?

AI models, such as Google's GraphCast and ECMWF's AIFS, already outperform traditional models in many comparisons at forecasting large-scale weather patterns (Lam et al. 2023). For local wind they do not have the edge yet: according to ECMWF's own comparison, the traditional model forecast the 10-metre wind better, and AI models underestimated peak winds in storms (Lang and Magnusson 2025; Charlton-Perez et al. 2024). In summer 2025, FMI's Sami Niemelä estimated that AI could be producing ordinary weather forecasts within a year or two (MTV Uutiset / STT, 28 June 2025). Gusts at the shore and the sea breeze, however, are still best seen in the detailed model and on a wind gauge.

Sources

Research

• Gahmberg, M., Savijärvi, H. and Leskinen, M. (2010): The influence of synoptic scale flow on sea breeze induced surface winds and calm zones. Tellus A 62(2), 209–217.
• Crosman, E. T. and Horel, J. D. (2010): Sea and lake breezes: A review of numerical studies. Boundary-Layer Meteorology 137, 1–29. doi:10.1007/s10546-010-9517-9
• Lam, R. et al. (2023): Learning skillful medium-range global weather forecasting. Science 382, 1416–1421. arXiv:2212.12794
• Lang, S. and Magnusson, L. (2025): AIFS ENS becomes operational. ECMWF Newsletter 185, 20–24. doi:10.21957/hg1z-pe65
• Charlton-Perez, A. J. et al. (2024): Do AI models produce better weather forecasts than physics-based models? A quantitative evaluation case study of Storm Ciarán. npj Climate and Atmospheric Science 7. doi:10.1038/s41612-024-00638-w

Weather services and other sources

• Ilmatieteen laitos (FMI): Merituuli ja maatuuli (sea breeze and land breeze), Tuuli ja myrskyt (wind and storms), Tuulet (winds), Havaintosuureet (observed quantities), Säätiedotus merenkulkijoille (weather forecast for shipping), Wind warnings, Numerical weather prediction and Kuinka pitkälle säätä voi ennustaa (how far ahead can the weather be forecast?). The pages with Finnish titles are in Finnish.
• ECMWF: Open data and interpreting a model grid-box value
• Beaufort scale: MeteoSwiss, following the WMO definition
• Warning thresholds elsewhere: SMHI and NWS
• EUMETRAIN: Sea breeze, satellite meteorology manual
• MTV Uutiset (Finnish TV news) / STT (Finnish News Agency) (28 June 2025): interview on AI in weather forecasting (in Finnish)
• Suomen Meripelastusseura (Finnish Lifeboat Institution): Ennen kuin irrotat köydet 2026 (Before you cast off 2026; PDF, in Finnish)