Sargassum levels across the Atlantic declined in August, but researchers say totals remain far above normal, leaving the U.S. Virgin Islands and the wider Caribbean at risk of inundations, according to a recent report from the University of South Florida’s Optical Oceanography Lab.
The OOL at USF uses satellite imagery to monitor the presence of sargassum across the Tropical Atlantic, Caribbean Sea, and the Gulf.
“As predicted in the sargassum bulletin in July 2025, total sargassum amounts in all but the eastern Atlantic region decreased in August,” according to an update from a sargassum outlook report released on Aug. 31 from the OOL at USF. “The most substantial decrease occurred in the Western Atlantic, from greater than 18 metric tons to six metric tons.”
“The decreases in the Gulf and Western Caribbean were minor because of the continuous influx arriving 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,” the update explained.
Cyclones and the Displacement of Sargassum
The Source connected with Brian Barnes, Ph.D., an assistant research professor at USF, who provided additional information about the effects on sargassum due to tropical cyclones, including Hurricane Erin, which passed just north of the USVI in mid-August.
Several beaches that had been inundated with seaweed prior to Erin’s passage were largely free of sargassum once the storm moved away from the region.
“The impact of hurricanes on sargassum is not always straightforward,” Barnes said. “We’ve seen both increases and decreases in abundance following previous storms. On the one hand, storms can mix in deep water, which is rich in nutrients, while on the other hand, the strong winds may batter or physically submerge the sargassum, such that it sinks. For Hurricane Erin, there was a substantial biomass reduction in the cyclone’s wake,” he explained.
Inundations are Still Possible Across the USVI
While a decrease in sargassum comes as good news, unfortunately, areas across the USVI and Puerto Rico will still likely experience inundations of the algae due to a large amount still in the ocean.
“As in previous years, the momentum of sargassum decline is likely to continue in the coming months, possibly reaching the annual minimum around October into November,” USF said. “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. Still, 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,” USF added.
“Despite overall declines, there’s still a lot of sargassum in the area, which means inundations are likely to continue in USVI,” Barnes said.
To deal with future accumulations of seaweed, local officials in the USVI have begun using floating barriers to divert incoming mats of sargassum before they reach the shoreline. However, while the booms have shown promise in keeping beaches clearer, they require constant upkeep due to strong currents and storm damage. The booms also need to be removed ahead of any possible approaching cyclones.
As was reported recently in a Source interview with Amy Dempsey, a marine biologist and environmental consultant and founder of the environmental consulting firm Bioimpact, Inc., additional booms are planned for the future.
While Dempsey confirmed that new deployments are being considered, funding remains a major hurdle. “The barriers are expensive, and unfortunately, someone has to be willing to put up the cost for the barriers, permitting, installation and monitoring.”
While most barrier deployments have been funded privately, Dempsey stressed the need for public investment and engagement, especially for protecting public beaches and nearshore habitats.
“We need to find funding sources so that public beaches and important resources can be protected,” Dempsey stated. “The public can advocate for financing through private funding to address this issue.”
Follow Sargassum Updates and the Weather Forecast
Individuals can follow the progression of the current mat of seaweed and stay up to date each month on where sargassum may be headed.
Finally, in addition to tracking the occurrence of sargassum, residents and visitors across the U.S. Virgin Islands are encouraged to continue monitoring the local weather forecast.
The National Hurricane Center is monitoring a tropical wave moving across the Atlantic Ocean with a high risk of development over the next seven days. The wave, currently designated as “Invest 91L,” is expected to intensify and could move close to the local region next week. Residents are urged to follow the forecast closely.
Meanwhile, the National Weather Service in San Juan, Puerto Rico, has warned that very warm temperatures will persist across the area, and heat alerts may be issued. Showers and thunderstorms are also possible as a separate, smaller tropical wave moves through the area on Friday. Additionally, Saharan dust will be present in the atmosphere Friday, creating hazy skies and reducing air quality.
Weather information is available from the NWS, the NHC, and NOAA. The local weather forecast for the U.S. Virgin Islands is regularly updated on the Source Weather Page and VI Source YouTube Channel, and individuals can also find helpful weather information and alerts from the Virgin Islands Territorial Emergency Management Agency.
St. Croix Source
Local news
