The generation and underlying dynamics of late-spring temperature and salinity fronts at the mouth of Block Island Sound in the Mid-Atlantic Bight are examined using a three-dimensional general circulation model. The model is forced by tidal velocities at its outer boundaries, an estuary/shelf salinity gradient, and surface warming. Runs representing the period from 18 April to 23 May 2000 are investigated through direct examination of the model results and diagnostic calculations that isolate individual processes. Three mechanisms are identified as significantly contributing to the location and structure fronts observed in this region. Vertical mixing produces the necessary horizontal temperature structure within and near Block Island Sound, but the southern frontal boundary is further affected by the subtidal circulation, which is divided into two components defined using a momentum budget analysis. Tidal currents over the complex bathymetry leads to nonlinearly rectified flows, including a headland eddy south of Montauk Point. Circumscribing this feature is a baroclinically adjusted, buoyant outflow from the Long Island Sound estuary. While modifications to the buoyancy forcing can modify the frontal position, it necessarily remains offshore of the tidally driven circulation. Analysis of the salinity anomaly fluxes indicates that both tidal and mean advection are responsible for the overall transport of buoyancy.