A perspective for the Caribbean Sea and Gulf of America* by the University of South Florida Optical Oceanography Lab

The map above shows the average Sargassum abundance for the month of August 2025, with warm colors representing higher abundance. The top color (red) indicates that 0.4% of the ocean surface is covered by Sargassum, meaning that Sargassum clumps and mats are scattered here and there in the location. The Sargassum abundance for each region is compared with historical values in the same month of 2011 – 2024 in the whisker box plot below, where horizontal bars in each vertical box indicate minimum, 25%, 50%, 75%, and maximal historical values, respectively.

As predicted in the last bulletin, total Sargassum amount in all but the East Atlantic region decreased in August. The most decrease occurred in the West Atlantic, from > 18M tons to 6M tons. The decreases in the Gulf of America and western Caribbean were minor because of the continuous supplies from the eastern Caribbean.

Some of the decreases in the eastern Caribbean and particularly to the north of the eastern Caribbean could be partially due to Hurricane Erin. Nevertheless, total Sargassum amount in every region still exceeded the historical record for the month of August. Significant Sargassum inundation events have continuously been reported around most Caribbean nations and islands, especially in the Mexican Caribbean.

Looking ahead: As in previous years, the momentum of Sargassum decline is likely to continue in the coming months, possibly reaching the annual minimum around October – November. However, because the absolute amount is still much higher than any previous August, Sargassum inundation of variable degree will continue to occur in most of the Caribbean nations and islands. However, 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. One such example is the southeast coast of Florida: although total Sargassum in the Gulf of America exceeded the historical record for 3 consecutive months, Sargassum inundation was not as severe as in some of the previous years, due mainly to the specific positions of the Loop Current and its eddies.

All previous monthly bulletins as well as daily imagery can be found under the Sargassum Watch System (SaWS).