Sources and methodology
The level shown for each beach estimates how likely you are to meet jellyfish. It combines several independent sources and is refreshed several times a day.
Official warnings
Thailand’s Department of Marine and Coastal Resources (DMCR) publishes jellyfish warnings at warning.dmcr.go.th. We check them every 3 hours and link them to the nearest beaches by place name and coordinates.
Weather, waves and currents
Wind, rain, wave height and direction, sea temperature and surface currents come from Open-Meteo, refreshed every 6 hours for today and 5 days ahead. Each beach’s orientation matters: what counts is wind from the sea.
A 2022–2026 climatology (ERA5 reanalysis and marine models) shows the usual wind and waves for each beach and month; the model also looks at how far conditions depart from that norm.
Beachgoer reports
"Jellyfish seen" and "no jellyfish" reports from this site. Unverified reports weigh less than verified ones; a moderator hides spam. Fresh sightings are carried forward with currents and wind, so beaches they may reach are warned in advance.
The trained model
Since October 2026 the risk level comes from a model trained on 6.6k dated observations from 2004–2026: official DMCR warnings and beachgoer reports. Training weather is the ERA5 reanalysis since 2008.
The model scores three groups separately: bluebottles, box jellyfish, and other jellyfish together with stinging plankton. For each it uses the area’s season (from how often they have been observed over the years) and how the day differs from a typical day of the same month: onshore wind and waves, the steadiness of onshore wind over 10 days, rain, calm sea and the beach orientation. Recent reports and drift are added on top.
The “typical day” norms for each beach and month (average wind, waves and rain) are computed from the same weather data the forecast uses, so the model compares each day with conditions that are normal for that beach rather than with another data source.
Bluebottles are predicted best, because the wind brings them. For other jellyfish and plankton the season and recent reports matter most: the exact day is hard to tell from the weather.
Reading the levels
Low — usual seasonal background, no reports. Moderate — conditions or nearby reports raise the chance. High — recent reports or unfavourable wind and waves. Very high — recent official or verified reports at the beach.
It is an estimate, not a safety guarantee: "no reports" does not mean there are no jellyfish. Follow beach flags and lifeguards.
Checking accuracy
Every day the 5-day forecast is stored and later compared with "jellyfish seen" and "no jellyfish" reports. Tests of the model on years it did not see in training and the live scores are published on the forecast page.