How accurate are our water temperatures?
We show you exactly what our numbers are: modelled estimates from the Open-Meteo marine and weather models, timestamped to the model run we cached. We never dress a model value up as a buoy measurement.
What each label means
- Current model estimate
- The value comes from a model run within the last two hours. Safe to read as today's conditions.
- Cached model estimate
- A run from earlier today, served instantly while a fresher run is fetched in the background. Sea temperature moves slowly, so this is usually within a few tenths of a degree.
- Model estimate / monthly average
- No dated run was available, so we fall back to long-term climatology for that location and month. Good for planning, not for today.
Where accuracy is weakest
- Enclosed bays, lagoons and marinas that heat far faster than the open grid cell.
- Estuaries and river mouths, where freshwater outflow changes temperature abruptly.
- Upwelling coasts (Portugal, California, Namibia) where wind can drop water 5°C in a day.
- Very shallow shorelines, where the first metre is warmer than the water 50 m out.
- Lakes and rivers, which are modelled with less observational input than the ocean.
Safety first
Temperature is only one part of safe swimming. Always follow local lifeguard advice, flags and water-quality notices. Cold-water shock can affect strong swimmers well above 15°C.
Common questions
Where do SwimTemperature water temperatures come from?
Every water, air, wave, wind and UV value on the site comes from the Open-Meteo marine and weather models, which assimilate satellite sea-surface temperature, buoy observations and numerical ocean forecasts onto a global grid. We do not operate our own sensors.
Are the readings measured or modelled?
They are modelled estimates, not in-situ measurements. Each page states whether the value is a current model run, a cached model run, or a long-term climatology average, so you always know what you are looking at.
How accurate is a modelled sea temperature?
For open-coast beaches, model sea-surface temperature is typically within about 0.5–1.0°C of a nearby buoy. Accuracy is lower in enclosed bays, lagoons, estuaries and shallow shorelines, where local heating, river outflow and wind-driven upwelling can shift the real water by several degrees within hours.
How often does the data update?
Live values refresh hourly from the model run. A pre-warmed snapshot is cached at the edge so pages render real temperatures immediately, then update in the background once the newest run is fetched.
What do the monthly averages mean?
Monthly tables show long-term climatology — the typical sea temperature for that month, averaged over many years. They describe what to expect when planning a trip, not conditions on a specific day.
Why does the temperature differ from what I felt in the water?
Sea-surface temperature represents roughly the top metre of open water at grid scale. Surface films warmed by sun, cold upwelling, thermoclines a metre down, tides and sheltered shallows all make the water you feel differ from the grid value. Treat readings as guidance, never as a safety guarantee.
Can I rely on this for cold-water safety decisions?
No. Always check local lifeguard, harbour and official water-quality notices before swimming. Cold-water shock, rip currents, jellyfish and pollution are not captured by temperature data.
Back to the live sea temperature map.