Built in St. Kitts & Nevis Sargasso Research ↗

Satellite map of sargassum density across the Atlantic in March 2023, from West Africa to the Gulf of Mexico.

Sargassum forecasting for St. Kitts & Nevis

Historical St. Kitts & Nevis tests show improved 48-hour sargassum drift maps. Separate drifter experiments develop crossing-probability methods toward coastal-risk forecasts.

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Built in St. Kitts & Nevis. Founded and built by Josiah Davis.

Problem

Sargassum arrives every year. The people responsible for the coast often know only when it is already there.

NASA visualization of monthly mean sargassum density in the Atlantic from January 2018 to December 2023.

Offshore blooms are difficult to translate into local impact

Satellite imagery can show material offshore, but raw imagery is not a decision. Turning it into local coastal risk is the missing step.

Sargassum washed up along a beach in Guadeloupe, south of St. Kitts & Nevis.

Cleanup is reactive when warning is poor

Crews and coastal managers usually mobilise once the seaweed is already on the sand, the most expensive moment to respond.

A handful of golden-brown sargassum seaweed.

Collected biomass still needs somewhere to go

Collection raises the next question: disposal or use. Planning either one needs a reliable idea of where and when material will show up.

Sargassum fluitans strands on Cocoa Beach, Florida.

The last stretch is the hardest to observe

Satellite visibility degrades close to shore and clouds leave gaps in the record, so near-shore arrivals are difficult to observe consistently.

Beach loungers on Pinney's Beach, Nevis.

Beaches and bookings take the hit first

Resorts, tour operators and fishers need days of notice to prepare. Without warning, a heavy landing becomes cancellations and lost working days.

What if we could see it offshore, understand where it is moving, and give St. Kitts & Nevis time to prepare?

That is what Sargasso is building.

What early warning changes

From reactive cleanup to days of notice

  1. Without warning

    The first notice is seaweed on the sand

    Crews mobilise after it lands, when cleanup costs the most and the smell has already reached hotels and homes.

  2. Days out

    Seen offshore

    Satellite passes pick up mats while they are still out in the Atlantic.

  3. Next 48 hours

    Drift forecast

    Currents and wind show where the material is likely to head, with the uncertainty stated.

  4. Before arrival

    Coastal outlook

    Coastal managers see which shores face elevated risk, in plain language.

  5. Landfall

    Ready when it lands

    Collection crews, hotels, boat operators and fishers plan the days ahead instead of reacting.

Cloud-free Sentinel-2 satellite view of St. Kitts and Nevis, rotated so both islands sit side by side.

Starting with St. Kitts & Nevis.

How it works

From open ocean to a coastal outlook

01 Observe

Pass · T+00 h

Satellite swath crossing the islands
Likely sargassum, one cell ≈ 600 m
Drift track Forecast position Surface current

Coastal outlook, next 48 h

  • Elevated Atlantic-facing coast
  • Moderate Partly sheltered shore
  • Low Caribbean (leeward) coast

Forecast vs. new observation

Observed Forecast

190 of 228 historical 48 h cases beat a no-movement baseline

Illustrative scenario on real geography

  1. 01

    Observe

    Satellite-derived observations identify offshore sargassum around St. Kitts & Nevis.

  2. 02

    Detect

    Machine-learning models separate likely sargassum from surrounding ocean observations.

  3. 03

    Forecast

    Ocean and atmospheric conditions are used to estimate how detected material may move over the following days.

  4. 04

    Translate

    Model output becomes a coastal outlook that is understandable to researchers, coastal managers and decision-makers.

  5. 05

    Improve

    Retrospective research compares model output with historical observations. Future forecasts will need validation against new observations and further local evidence; Sargasso does not issue public live forecasts.

Forecasts are probabilistic, and near-shore conditions are harder to observe. Sargasso reports likelihood and uncertainty rather than certain beach landfalls. The scene above is an illustrative scenario drawn on a Sentinel-2 view of the islands, not a live forecast.

Technology & research

One pipeline, from satellite pixels to local risk

Sargasso combines satellite remote sensing, computer vision and ocean data into a forecasting pipeline built for St. Kitts & Nevis.

  • Satellite remote sensing
  • Segmentation and computer vision
  • Historical satellite observations
  • Drift forecasting
  • Physics-informed modelling
  • Ocean current and wind information
  • Coastal risk estimation
  • Model validation and local evaluation
Satellite image of a vast sargassum bloom in the Atlantic Ocean.
Satellite view of a sargassum bloom in the Atlantic. Source: NASA Earth Observatory.
NASA visualization of simulated sargassum drift paths across the Atlantic with a release timeline.
Simulated drift paths, traced back from the Caribbean through 2010 and 2011. Source: NASA Scientific Visualization Studio.

In a historical 48-hour St. Kitts & Nevis test, frozen Sargassum forecast maps improved mean overlap by 18.9% over a persistence baseline across 228 cases. This is a retrospective map benchmark, not beach-level or live-service validation. See the result and recent drifter probability research.

View the research on GitHub ↗

Why it matters

A local problem with a long memory

  • 2011

    First basin-scale sargassum year

  • 8,850 km

    Belt extent at its 2018 peak

  • 20 Mt

    Estimated biomass in the 2018 belt

  • Daily

    Satellite observations over the region

Sources: NASA Earth Observatory; Wang et al., Science, 2019.

Coastal satellite image of sargassum approaching the Dominican Republic.
Sentinel-2 view of sargassum approaching the Dominican Republic coast. Source: ESA Copernicus.
  • The Great Atlantic Sargassum Belt forms, drifts and lands on coastlines across the region, including ours.
  • Rotting sargassum releases hydrogen sulfide, which fouls the air and can aggravate respiratory conditions.
  • Thick mats stress coastal water, seagrass beds and nesting beaches.
  • Cleanup, disposal and lost beach days land on local budgets and local businesses.

In 2018 a single belt held more than 20 million tonnes of sargassum and stretched 8,850 km across the Atlantic.

The record

The belt is measured every year

Satellites have watched the Atlantic belt since 2011. This animation runs through July of every year from 2010 to 2023.

July mean sargassum, 2010 to 2023. Each box is a half-degree cell, roughly 3,025 square kilometres, coloured by the average amount of sargassum observed in it. Source: NASA Scientific Visualization Studio, from MODIS observations via the University of South Florida.

Published estimates vary across years and months. Basin-scale satellite monitoring describes the wider Atlantic belt, not local beach conditions. Sources: Wang et al., Science, 2019; University of South Florida satellite monitoring.

Research & partnerships

Working on sargassum in St. Kitts & Nevis?

Sargasso is interested in working with organisations involved in coastal management, environmental monitoring, tourism, research, ports and marine operations, and sargassum collection or utilisation.

Let's compare notes

We do not list partners until a collaboration is confirmed.

About

Built in St. Kitts & Nevis

Sargasso began in St. Kitts & Nevis with a simple question: if satellites can already see sargassum offshore, can we turn that information into something our islands can actually use before it reaches the coast?

Founded and built by Josiah Davis, Sargasso combines machine learning, remote sensing and ocean data to develop local sargassum forecasting infrastructure.

Let's talk

Josiah Davis

Founder, Sargasso

St. Kitts & Nevis

[email protected]

github.com/Jstarzz/Sargasso-Research ↗

The road along St. Kitts' southeast peninsula, with Atlantic surf on one side.
Frigate Bay, St. Kitts, seen from the Timothy Hill overlook.

FAQ

Straight answers about sargassum forecasting

What is Sargasso?

Sargasso is a local research project on sargassum, in development. It combines satellite-derived observations, machine learning and ocean data to study offshore sargassum, track its movement and estimate where it may approach St. Kitts & Nevis. It does not currently issue a public live forecast.

Why start with St. Kitts & Nevis?

Because this is home. A focused regional study gives the project a place to connect satellite observations, drift estimates and coastal questions before considering other islands.

What data does Sargasso use?

Open satellite observations, ocean and atmospheric conditions, and environmental forecast data. The exact sources and processing steps are documented in the research repository.

How far ahead can it forecast?

A historical Sargassum-specific test evaluates 48-hour drift. Separate historical tests of undrogued drifters examine crossing probabilities at 48 and 120 hours; those horizons are not Sargassum forecast validation. These are research results, not forecasts issued to the public; Sargasso does not issue a public live forecast. Cloud cover, sea state and distance from shore affect what a future forecast could say.

Can it predict the exact beach where sargassum will land?

Model 1 detects sargassum in satellite imagery, Model 2 estimates drift, and Model 3 is being developed to translate movement into coastal risk. Historical drift results and crossing-probability tests show progress toward that goal, but they do not establish reliable arrival at a particular beach and time. The current research archive lacks independent beach-positive observations paired with forecasts frozen in advance; that is the next evidence needed to assess beach-level skill.

How are forecasts validated?

The strongest Sargassum-specific historical benchmark covers 228 nominal 48-hour cases around St. Kitts & Nevis. Frozen forecast maps scored 0.5152 mean IoU versus 0.4334 for persistence, a paired relative improvement of 18.9%, with 190 wins, 3 ties and 35 losses. This owner-supplied aggregate has not been independently reproduced and does not measure beach-level or live-service skill. Recent probability and drift results use separate non-Sargassum drifter datasets.

What do the benchmark results show?

The frozen historical test shows improved 48-hour map overlap over a persistence baseline on 228 Sargassum cases around St. Kitts & Nevis. Separate drifter experiments inform probability methods. Neither result establishes beach-level arrival skill; independent dated beach observations paired with forecasts frozen in advance are the next validation step.

Is the research public?

Wherever we can, yes. Development notes, experiments and model work are published through the Sargasso Research repository on GitHub.

Will coverage expand beyond St. Kitts & Nevis?

That is the long-term direction, and it is deliberately separate from the current focus. The pipeline is designed to extend to other islands once it works properly here.

Follow the research

The work is published openly

The research page brings together the Sargassum-specific 48-hour benchmark, recent calibrated crossing-probability work, and drifter experiments that inform the method. The local guide explains floating sargassum and coastal arrivals.

Research and recent progress Sargassum in St. Kitts & Nevis

Open the research archive ↗