The surface coastal circulation in and off the Block Island Sound (BIS) is examined based on one- year HF radar (CODAR) observations, bottom-mounted Acoustic Doppler Current Profiler (ADCP) moorings, and a three-dimensional, primitive-equation model to characterize the buoyant flow patterns and their temporal evolution. Three analysis methods, visual sorting, Self-Organizing Maps (SOM) and Empirical Orthogonal Functions (EOF), are used and their results are compared. The Princeton Ocean Model (POM) is also applied to study the three-dimensional barotropic semidiurnal tidal response in the New...