Sargassum Tracker

USF OOL Long Term Outlook

Sep 30, 2025
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As in previous years, the momentum of Sargassum decline continued in September, with total Sargassum amount in each of the five regions decreased. The decline was substantial in all but the East Atlantic region, with total Sargassum amount more than halved. Most Sargassum is now in the eastern Caribbean region, followed by the East Atlantic. In the Gulf of America, Sargassum amount decreased from 1.9M metric tons in August to 0.6 M metric tons in September, yet due to changes in ocean circulation the amount of Sargassum reaching the Straits of Florida increased, likely causing more inundations along the SE coast of Florida. Despite the overall declines, total Sargassum amount in every but the East Atlantic region still exceeded the historical record for the month of September, and inundation pressure around many Caribbean regions is still high.

Looking ahead: Total Sargassum amount in all regions is likely to continue to decline, possibly reaching the annual minimum around October – November. However, because the absolute amount is still much higher than any previous September, Sargassum inundation of variable degrees will continue to occur, especially along the Mexican Caribbean coast and around Haiti, Dominican Republic, Puerto Rico, U.S. Virgin Islands, among others. On the other hand, whether a beach or small region receives large amount of Sargassum depends on local factors that are difficult to predict, including winds and ocean currents. More info: Sargassum Watch System (SaWS).

SARGASSUM ABUNDANCE INTENSITY

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Since 2011, large amounts of Sargassum seaweed have appeared in the Caribbean Sea every summer except 2013, creating many environmental, ecological, and economic problems in many regions. The seaweed originated from the tropical Atlantic and is believed to be a result of climate variability and other natural and unnatural processes. Based on satellite observations and statistics of historical events, in early February 2018, the Optical Oceanography Lab developed the first 1-page Sargassum outlook bulletin for the Caribbean Sea. Since then, the bulletins have been generated and distributed to subscribers by the last day of the month. These monthly bulletins are also made available at the bottom of the SaWS page.

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Disclaimer

The information bulletin is meant to provide a general outlook of current bloom condition and future bloom probability for the Caribbean Sea. By no means should it be used for commercial purpose, or used for predicting bloom conditions for a specific location or beach. The authors of this bulletin, as well as Caricoos, USF and NASA, take no responsibility for improper use or interpretation of the bulletin. Any use of the image, data, or graph from this bulletin page in reports or publications should obtain permission from the USF OOL group.