Where this data comes from
The Virginia Jellyfish Report is a free beach-check site. We do not model jellyfish ourselves. We republish and explain the sea nettle forecasts made by two trusted public science groups, and we translate them into plain labels for Virginia beaches.
Our two sources are:
- The VIMS sea nettle probability forecast, from the Virginia Institute of Marine Science.
- The NOAA NCCOS Chesapeake Bay sea nettle forecasts.
Both publish daily map images that show where sea nettles are likely across the Chesapeake Bay and its rivers. We build our beach pages on top of those maps.
What the numbers actually mean
This is the most important thing to understand. The values on these maps are a modeled percent chance of encountering sea nettles, not a count of how many jellyfish are in the water. A reading of, say, a high chance means the model expects sea nettles to be likely there, not that a certain number of jellyfish were counted.
The forecasts are driven mainly by water temperature and salinity, the two conditions that most control where sea nettles turn up. Because it is a model, it describes likelihood, not a guarantee. You can have a light reading and still see a nettle, or a heavy reading on a day the water happens to be clear at your feet.
How we turn maps into labels
Here is our process, in plain terms:
- Each day we archive the public forecast map images from VIMS and NOAA. Both sources overwrite their images, so keeping our own snapshots lets us build a record over time.
- For each Virginia locality, we read the modeled values from the maps in the water near that place.
- We translate those values into simple labels like Light, Moderate, and Heavy, so you do not have to read a color scale to get the gist.
- We save each day's reading, which lets the pages get more useful over time and eventually show whether a spot usually runs high or low.
The maps update daily, so the labels on the home page and the local pages reflect the latest available forecast.
Honest limitations
We want you to trust this site, so here is where it falls short:
- It is a model, not a measurement. The forecast estimates likelihood from conditions. It does not watch the water at your beach.
- We read images, not raw model data. Reading values off map pictures is less precise than using the underlying model grid. We keep improving this, but a single beach reading is an estimate.
- Coverage varies. Some areas sit at the edge of the maps or have weaker source coverage. The Virginia Beach oceanfront, for example, is not well covered by the regional NOAA pages, and the bay-focused forecasts are less meaningful on the open Atlantic.
- Other jellyfish are not tracked. The forecast is for sea nettles. It does not track moon jellies, lion's mane, comb jellies, or the rare Portuguese man o' war. See our species guide for those.
- Local conditions change fast. Wind, tide, and currents can push jellyfish around within a day. Always look at the water before you swim.
Why we keep our own archive
Both VIMS and NOAA overwrite the same image addresses each day, so yesterday's map is gone once today's is posted. By saving our own copy every day, we can build a record over time. That record is what lets a beach page eventually say whether a spot usually runs high, usually runs low, or varies a lot through the season. Early on, a page mostly shows today and tomorrow, but the history behind it grows with each daily run.
We also keep the reading tied to the specific water near each locality rather than a single bay-wide number. Two beaches in the same city can sit on different rivers with different salt levels, so a nettle-heavy river mouth and a fresher upstream cove deserve different labels even on the same day.
How to use it well
Treat this site as a quick, useful check, not a promise. Look at the daily label, compare a couple of nearby beaches, and use common sense at the shoreline. For planning, the season guide explains the yearly pattern, and the how to avoid jellyfish guide has practical tips. If you get stung, see our sting first aid guide.
For the science behind the forecasts, go straight to the sources: VIMS sea nettles and NOAA NCCOS.
Who runs this site
The Virginia Jellyfish Report is a small independent project run from Virginia. It is not affiliated with VIMS, NOAA, or any government agency; we simply archive and translate their public forecasts so beach decisions take seconds instead of a scavenger hunt through research sites.
Local knowledge makes the site better. If a beach detail is wrong, a spot is missing, or the water you swam this morning did not match our label, use the contact page and we will take a look. You can read what little we collect about visitors in the privacy policy.
How we read a city or county
Each city and county gets a handful of fixed checkpoints in the waters where people actually swim, not out in the middle of the shipping channel. Every morning we read the day's forecast maps at those checkpoints, from the closest NOAA regional view plus the statewide VIMS map, and take the middle value so one odd spot on the map cannot skew the whole area. That number becomes the day's percent and its Light, Moderate, or Heavy label.
How we read a specific beach
Beaches are more precise. Each named beach has a single researched point in the water just off the sand, placed by hand and double-checked on a map, and we read a small circle around that point. That is why a beach and its city can disagree: Buckroe Beach and the middle of Hampton's waters are different places, and the beach page tells you about the beach. When a beach does not have its own point yet, its page uses the nearest area reading and says so.
When the forecast is wrong
Sometimes it is. The model predicts the chance of sea nettles from things like water temperature and saltiness, but it cannot see the actual jellyfish that a wind shift or tide just pushed toward the sand. There have been days when a beach read low on our maps while lifeguards there were flying a purple flag, the signal that dangerous marine life has actually been seen. So treat this site as your planning tool, not your lifeguard: check the flags when you arrive, and if the flag and the forecast disagree, the flag wins every time.