Floating Materials in Tampa Bay and Charlotte Harbor, Florida, USA after Hurricanes Helene and Milton

Within 14 days between September 26 and October 9 of 2024, Hurricanes Helene (Category 4) and Milton (Category 3) made landfall on the west coast of Florida (U.S.A), causing compounding damage due to their strong winds, heavy rainfall, and severe storm surges. Despite extensive post-hurricane damage assessments on land, the distribution and fate of floating debris in the estuarine and marine environments remain unknown. Here, using Sentinel-2 Multispectral Instrument (MSI) satellite imagery (10 m resolution), aerial photographs, and spectral analysis, we show the possible types, distribution, and temporal changes of hurricane-induced floating materials in estuarine and coastal waters off west-central Florida, including Tampa Bay and Charlotte Harbor. Spectral characteristics and visual patterns suggest that these floating materials consisted of offshore dead vegetation (e.g., seagrass and tree branches), vegetation-debris mixtures (with possible plastics), and non-vegetation materials in the two estuaries. Following Helene, floating materials peaked three days after landfall on September 29 (estimated 136,000 m² in Tampa Bay, 22,000 m² in Charlotte Harbor) and nearly vanished in five days. After Milton, peak coverage occurred five days after landfall on October 14 (110,000 m² in Tampa Bay, 133,000 m² in Charlotte Harbor) and persisted for at least 15 days until October 29. Ocean current analysis further suggests that the post-Milton offshore floating materials west of Tampa Bay mainly originated from Helene-induced remnants in the Big Bend region. These findings shed light on combining satellite and airborne remote sensing to map floating debris and other floating materials after hurricanes, which may help mitigation efforts in the future once such an approach is implemented for near-real-time applications.