Improvement of Sargassum Seaweed tracking in Puerto Rico and Virgin Islands Using High-Resolution FVCOM

Since 2011, significant accumulations of Sargassum have been a recurrent problem in the Caribbean Sea, the Gulf of Mexico, and the tropical Atlantic. The accumulated piles of sea-weed caused by landfalls are detrimental to coastal tourism and lead to health risks for tourists and nearby residents. Caribbean Coastal Ocean Observing System (CariCOOS) developed and implemented Sargassum trajectory forecasts in the coastal area of Puerto Rico and the Virginal Islands (PRVI), based upon surface current forecasts from the operational AmSeas/FVCOM ocean model and direct surface measurements from High-Frequency Radars (HFRs), to accurately predict the beaching events and mitigate its negative impacts. Alternative Floating Algae Index (AFAI) product and Maximum Chlorophyll Index (MCI) were used to monitor the dispersal of Sargassum. In this work, floating virtual particles were released at the locations of high Sargassum concentration explicitly visualized by MCI and advected using a data-assimilated FVCOM model to estimate where the Sargassum would drift, as well as the spots of potential landfall occurrence. A reoccurring trajectory model was used to minimize the growth of separation between modeled and observed results. By frequently re-initializing the trajectory models with satellite observations, the sargassum trajectories and aggregations were better predicted before landfalls. The result was validated by the corresponding beaching events recorded by Experimental Weekly Sargassum Inundation Report and other media. It is found that FVCOM is likely to be capable of forecasting the potential Sargassum inundation in a lead time of more than five days with the MCI image assimilation scheme.