Sargassum in St Barth

How the risk is estimated

1. Satellite: the NOAA SIR (Sargassum Inundation Risk) product detects sargassum rafts offshore of the Antilles. It is reliable more than 30 km from the coast, less so near the shore.
2. Drift: from the wind (Météo-France AROME 2.5 km model), surface currents and swell, we compute where the detected rafts are heading and whether they can reach the bay.
3. Bay geography: Saint-Jean Bay opens to the north-north-east. Depending on whether the flow pushes towards the shore or along it, the risk differs for the beach, the bay and offshore.
4. Field checks: observations by the on-site team override the day's estimate as soon as they are entered.

Season, health and beach

• Sargassum landings in the Caribbean are most frequent from spring to late summer, but vary a lot from year to year.
• Fresh seaweed at sea is harmless to touch; however, mats decomposing on the shore release hydrogen sulphide (rotten-egg smell): avoid staying close to them for long.
• An affected beach can clear within hours if the wind shifts: check today's forecast and photos before giving up.