This study used the coupled ocean-atmosphere regional model (COAWST) to evaluate the effect of the trapped wave formed by a frontal system over the Southern Brazilian Continental Shelf (SBCS) during September 2016. The oceanic model was configured for the domain of 20–40°S/40–60°W, with a horizontal resolution of 1/9°, 32 vertical levels, and forced with Global Ocean Sea Physical Analysis and Forecasting Products. The model simulations were compared to remote sensing and tide gauges data, with a correlation higher than 0.78 between the wind and sea level rise data and higher than 0.82 for the wave amplitude and phase. Our results showed the presence of a sea level anomaly propagating northward along the continental shelf at 480 km.day−1, probably associated with the presence of a coastal-trapped wave. The analyzed period consisted of the rapid formation of an extra-tropical cyclone on the model grid, intensifying the south-quadrant winds and the associated Ekman transport. The zonal acceleration and Coriolis terms were strongly associated with the wave crossing, with an amplitude greater than 2.10−5 m.s−2. The Coriolis term follows the geostrophic flow induced by the wave crest, with values greater than 4.2 m.s−2, and a correlation coefficient of 0.82 with the pressure gradient and friction terms. The trapped wave reversed the pressure gradient and the over-shelf flow with a negative geostrophic flow (average westward shelf flow). Our results reinforce the fact that these processes change the physical and chemical seawater properties over the SBCS, changing the mixing layer and fertilizing its shelf waters.