Sargassum Atlas
Atlantic + Caribbean sargassum monitoring. The brown belt clogs raw-water intakes, fouls props, and traps you in calms — plan your route around it.
Live tracking
USF SAWS — Sargassum Watch System University of South Florida Optical Oceanography Lab. Monthly satellite-derived density maps for the Atlantic, Caribbean, and Gulf of Mexico. The authoritative source. SAWS monthly bulletins (PDF) USF's monthly Outlook + Inundation reports — written interpretation of where the belt is and where it's heading. NOAA AOML Sargassum Inundation Report 7-day forecast of Caribbean shoreline inundation risk, region-by-region. Good for picking landfall ports. NOAA CoastWatch Sargassum Near-real-time satellite imagery and density anomalies.
Why it matters underway
- Engine cooling — sargassum mats jam raw-water strainers within minutes in heavy concentration. Carry spares; check the strainer hourly when transiting a known belt.
- Propulsion — wraps around props and shafts; cutters help but don't always clear thick mats.
- Sailing — slows the boat, fouls speed/depth transducers, and can trap you in light air. Belts often align with N-S current shears, so the wind is already weak.
- Fishing gear — drag lines pick up clumps that look like strikes.
- Anchorages — heavy inundation makes some Caribbean lee shores unusable in season (Apr–Aug peak).
Routing tactics
- Plan around the belt, not through it. The Great Atlantic Sargassum Belt (GASB) typically stretches from West Africa to the Caribbean across 5°N–20°N. SAWS density maps show where it's thickest in the current month.
- Stay north or south of the GASB when possible. Trade-wind passages from the Canaries to the Lesser Antilles in Apr–Aug routinely hit it; coming further south to ~5°N or further north often misses the worst.
- Watch for ribbon-like windrows aligned with the wind — those are where it concentrates and you can sometimes thread between them.
- Caribbean landfall — east-facing shores (Barbados, Tobago, eastern Lesser Antilles) get the brunt; lee-side bays are usually clean. Check AOML's 7-day inundation forecast before committing to a port.