Beach trips: sargassum is peaking

If you’re flying to South Florida or the United States Caribbean in April, the thing to watch is not a storm map but a seaweed map: the latest University of South Florida bulletin says sargassum kept growing through March, and the Florida Keys and southeast Florida are likely to see moderate beaching in the coming month. (optics.marine.usf.edu) This is not seaweed growing on the beach. Sargassum is a floating brown algae that stays at the ocean surface, forms mats in open water, and then gets pushed ashore by currents and wind. (coastwatch.noaa.gov) The reason beachgoers notice it so fast is simple: a scattered mat offshore can turn into a thick line on sand once waves pile it up in one place. NOAA and the University of South Florida now publish weekly “inundation risk” maps that estimate where that shoreline pileup is most likely. (cwcgom.aoml.noaa.gov) Those weekly maps are built from satellite measurements, then compared with a recent baseline inside a 50 kilometer coastal zone. The system sorts each stretch of coast into low, medium, or high risk, and NOAA says the product is updated every Tuesday. (cwcgom.aoml.noaa.gov) The bigger shift started in 2011, when massive amounts of sargassum began moving west into the Caribbean Sea, the Gulf, Florida, Puerto Rico, and the United States Virgin Islands instead of staying mostly in the Sargasso Sea. NOAA says researchers are still testing causes, including unusual wind shifts, river outflow, nutrient levels, Saharan dust, and warmer water. (coastwatch.noaa.gov) This year is running hot already. The University of South Florida said January 2026 Caribbean sargassum jumped from about 0.45 million tons in December 2025 to 1.7 million tons in January 2026, and February stayed at record highs across most monitored regions. (optics.marine.usf.edu 1) (optics.marine.usf.edu 2) By March, the bloom had spread farther west, with the University of South Florida saying every region on its map except the eastern Atlantic was still at record-high levels for that month. The lab’s public update says 2026 looks like another major sargassum year and likely a record year. (optics.marine.usf.edu 1) (optics.marine.usf.edu 2) NOAA’s new twist is scale. In January 2026, the agency said its scientists were pairing artificial intelligence with more than 1 million satellite images to detect and measure floating seaweed and other surface blooms across the global ocean, giving researchers a much longer record than a single beach camera or cleanup report. (nesdis.noaa.gov) That matters because sargassum season usually builds in spring and summer, when warmer water and nutrients help growth. NOAA says moderate blooms can help ocean life, but extensive and longer-lasting blooms can hit tourism, fishing, and coastal businesses. (nesdis.noaa.gov) The catch for travelers is that regional outlooks are good at saying “this month looks busy,” but not “this exact beach will be clear at 2 p.m.” The University of South Florida says its bulletin is for broad regional outlooks and should not be used to predict conditions for a specific beach. (optics.marine.usf.edu) So the practical read on April 10, 2026 is narrow but useful: Florida’s Atlantic side, the Florida Keys, Puerto Rico, the United States Virgin Islands, and other Caribbean coasts can all see nuisance-level arrivals now, and the odds stay elevated as April progresses because the offshore bloom is still growing and drifting west. (optics.marine.usf.edu) (cwcgom.aoml.noaa.gov)