Sargasso Check
About and methodology
Sargasso Check is a project by Julie, a French-Canadian entrepreneur. It helps travellers and travel agents anticipate sargassum on a hotel beach in the Caribbean or Mexico.
Who it is for
Travellers choosing a hotel want to know what the beach may feel like. Travel agents want a compact check they can send to a client. Both read the same status, the date of the latest observation, and the recent history.
The index
Each day the site stores the median USF AFAI between 35 and 70 km from the hotel. The first 35 km are left out. On the Riviera Maya the 12–35 km band stays high while the water past 35 km is negative: that is the shelf and the 7-day composite, not a mat offshore. A negative median is clear offshore water (None). From 0.0004 the status is Low, up to 0.001 Moderate, and from 0.001 High — and only if a recent day was already above 0.0004, so a one-day glint spike cannot be High. Fewer than 8 usable sea pixels in that ring is Data unavailable. A beach report from the last 14 days, when we have one, replaces that badge. A shoreline signal with clear water past 35 km can only raise the status to Low.
| None | index below 0.0000 |
|---|---|
| Low | from 0.0000 to less than 0.0004 |
| Moderate | from 0.0004 to less than 0.0010 |
| High | 0.0010 and above |
| Data unavailable | no usable index |
An index below 0.0000 is None. The grid is 0.015° (about 1.7 km), so a few hundred metres of beach cannot be resolved. The field is a 7-day composite, updated daily, and can be a few days behind.
Source and licence
The numbers come from the 7-day cumulative USF AFAI fields on the NOAA AOML CoastWatch ERDDAP (dataset noaa_aoml_atlantic_oceanwatch_AFAI_7D). AFAI, the Alternative Floating Algae Index, is estimated by Chuanmin Hu at the University of South Florida Optical Oceanography Laboratory (Sargassum Watch) from MODIS and VIIRS. NOAA AOML Atlantic OceanWatch distributes the grid. No API key is required.
Reference: Hu, Feng, Hardy, and Hochberg (2015), Remote Sensing of Environment 167:229–246. The data may be used and redistributed for free. They are not intended for legal use and can be inaccurate; NOAA and USF give no warranty. AFAI saturates in cloud, sun glint, and thick aerosol, which is why a day with too few valid pixels stays unavailable.
The daily refresh is python3 scripts/update-sargassum.py, also scheduled in .github/workflows/sargassum.yml.
Catalogue
The hotel list is a 5 November 2026 inventory of beach hotels in the Caribbean and Mexico. It is a reference catalogue, not a guarantee that a room is for sale on a given date. Coordinates are approximate hotel points, not beach polygons. Hotels without coordinates stay in the list and are left off the map. Cuba is not in the catalogue.
Pacific-coast hotels (Los Cabos, Puerto Vallarta, Acapulco, and the other Pacific markets) do not receive a sargassum status: Atlantic sargassum does not reach that coast.
Shoreline statuses and histories on this site are computed from that satellite grid, not from a demonstration series. Hotels without coordinates stay off the map and have no index.