The maps below show Sargassum abundance, with warm colors representing high abundance. In April 2021, the Sargassum amount increased across the central west Atlantic (CWA) and the Caribbean Sea (CS), while decreased in the central east Atlantic (CEA). Large amount of Sargassum was observed in the CWA, i.e., the region east of the Lesser Antilles in the maps below, and the eastern CS. Moderate amount was observed in the western CS, with large rafts observed 250 km NE of Costa Rica by end of April. In other regions, Sargassum amount remained to be small. These regions include the Gulf of Mexico (GOM) and the Florida Straits. Sargassum transport from the CS to the GoM through the Yucatan was observed. In all regions combined, the total Sargassum amount increased from ~10.1 M tons in Mar 2021 to ~10.6 M tons in Apr 2021, only second to Apr 2018 (12.6 M).

Looking ahead, both the eastern and western CS will likely experience increasing amounts of Sargassum in May to July 2021. Some of the Lesser Antilles Islands will continue experiencing beaching events on both their windward leeward beaches. The GoM will experience more Sargassum transport from the CS. This situation may continue into summer, and the overall bloom intensity is likely to be higher than in 2019. We will keep a close eye on how Sargassum in the CS and the tropical Atlantic may evolve in the next two months. More updates will be provided by the end of May 2021, and more information and near real-time imagery can be found under the Sargassum Watch System (SaWS, https://optics.marine.usf.edu/projects/saws.html).