Microplastic contamination in the ocean has emerged as an environmental issue of global importance. The most effective strategy to control microplastic pollution is to reduce the terrestrial input, but severe weather conditions make it difficult. This study investigated microplastic abundance and characteristics in the seawater, sediments, and cultured oysters (Crassostrea gigas) of Sanggou Bay (China) before and after two typhoons with an average rainfall of 19.2 mm/d over 8 days. Prior to the typhoons, microplastic levels in the seawater, sediment, and oysters were 63.6 ± 37.4 items/L, 2178 ± 369 items/kg, and 41.0 ± 15.5 items/individual, with fibers being the predominant shape. Typhoons increased the average concentrations of microplastics in the seawater and sediments by approximately 40%, and the proportions of fragments, spherules, and granules in the sediments increased by 9.6%, 4.0%, and 4.3%, respectively. The majority of microplastics in seawater, sediments, and oysters collected before the typhoons could be grouped into sizes of 0.1–0.5 mm (36.7%), 0.05–0.1 mm (42.6%), and 0.1–0.5 mm (47.1%), respectively. After the typhoons, the most abundant size classes of microplastics in the three environmental compartments were 0.05–0.1 mm (39.2%) for seawater, 0.1–0.5 mm (37.1%) for sediments, and 0.05–0.1 mm (29.9%) for oysters. The typhoons also altered color distribution of microplastics and increased the proportions of polypropylene, polystyrene, and polyethylene terephthalate in seawater. Scanning electron microscopy/energy dispersive spectroscopy showed that organic matter and heavy metals were present on the microplastics collected from oysters. Our results suggest that weather conditions should be considered when investigating marine microplastics.