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St Lucia sargassum forecast

Island · Covers: St Lucia.

Next 72 hours (this week)
Loading the latest forecast…
Days 4–7: no reliable model yet. Weed near this region in the 12 days to 6 October 2026 was falling compared with the 12 days before.
Next 30 days (this month)
LowerLower than usual
41% likely. Lower 41% · About usual 33% · Higher 27%.
In tests on 11 past years the most likely category was right 43% of the time (33% would be guessing).
Next 3 months
LowerLower than usual
43% likely. Lower 43% · About usual 31% · Higher 25%.
In tests on 11 past years the most likely category was right 42% of the time (33% would be guessing).

Coasts most at risk in the next 72 hours

Open the map zoomed to St Lucia
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Nutrients & runoff view: Lesser Antilles
Opens the map on the Lesser Antilles nutrient & runoff layers (nitrate, phosphate, green water, sea temperature, river water), colour scales tuned to that region. Sargassum absorbs dissolved nutrients from the water; it does not eat plankton.

Charts

Next 3 days: weed coming ashore

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How much seaweed our drift model brings onto this region's shores on each of the next 3 days (all shores added up; amount × share of model runs). Taller = more weed. Zero means none reaches the shore in the model.

Last 12 months vs usual

Share of the sea around St Lucia (a box about 234 km across) where satellites saw seaweed, month by month (gold), against the usual range for that month in past years (blue band). Above the band = a heavier month than usual.

Typical year, with 2026 highlighted

The grey line is the average for each month since 2016: it shows the season. Peak months here: May, Jun, Jul. October is usually a quieter month. Gold is this year so far.

Year by year

Average share of sea with seaweed for each year. 2026* is the year so far (January–October).

How to read this

Next 72 hours
We take today's satellite detections of floating sargassum and drift them with forecast ocean currents and wind for 3 days, many times with small changes. Heavy, moderate and light describe how much weed reaches a shore and in how many of those runs; quiet means none of the runs bring weed ashore. The model only looks 72 hours ahead, so “this week” beyond day 3 is a trend, not a forecast.
Next 30 days and next 3 months
These are outlooks, not precise forecasts. We compare the amount of weed around the region in the last 12 days with what is normal for the time of year (10 years of NOAA AOML satellite data) and, from how such situations played out in past years, give the chance that the coming period will be lower than usual, about usual or higher than usual. “Usual” means the middle third of past years for the same dates. If no category reaches 40%, we say there is no clear signal. These outlooks are experimental.
Likelihood and confidence
“60% likely” means that in situations like this one, that outcome happened about 6 times in 10. A 33% chance is the same as a guess with three options. The “right X% of the time” line is how often the most likely category matched what really happened when we re-ran the method on past years it had not seen.
Why forecasts can be wrong
Clouds hide weed from satellites, small rafts are missed, winds and currents can differ from the forecast, and local beach clean-ups or reefs change what you actually see on the sand. The seasonal outlooks only use past weed amounts, not future weather.
How accurate is it?
The 72-hour drift landings for this region are still being validated against satellite and beach reports; we don't publish an accuracy figure for them yet.
How often it updates
The 72-hour forecast is recomputed several times a day (this page shows the latest run, cached for up to 6 hours). The 30-day and 3-month outlooks and the charts use satellite data up to 6 October 2026 and are refreshed monthly.