This thesis investigates the physical processes in the Santos-São Vicente-Bertioga Estuarine System (SS-VBES) using observed and modeled data. The goals of this study are: the description and validation of the Santos Operational Forecasting System (SOFS) implemented to monitor and predict short-term (< 3 days) sea surface elevations and surface currents in the SSVBES (Chapter 2); the characterization of the physical processes of the estuarine dynamics in the SSVBES focused in the Porto Channel (Chapter 3); and the assessment of possible climate change-induced storm tide modifications in terms of number and intensity of events in the SSVBES (Chapter 4). The observed data used for this analysis include real-time sea surface elevations and surface currents collected by the Santos Pilots in stations placed along the Porto Channel; and the hydrographic and current measurements from the ECOSAN cruises collected at the entrance of the same channel. The numerical simulations were performed with the Princeton Ocean Model (POM) version POM-rain. The implementation of the model comprises two one-way nested grids, a coarse resolution for the South Brazil Bight (SBB) and a high resolution grid for the SSVBES. The SBB grid is forced by winds, density gradients and the Brazil Current flowing offshore. The SSVBES grid is forced by the SBB elevations and density fields, tides, winds and river runoff. The performance of the SOFS, tested in Chapter 2, showed that the accuracy of modeled sea level and surface currents reaches O (10) cm and O (10) cm/s, respectively. Seven recent (since 2016) storm tides were simulated with average skills of 0.95 and average root mean square errors of 17.0 cm. The SOFS is the first operational system in the SSVBES able to simulate and predict the 3D currents within the estuary, also nested in an unprecedented forecasting system for the SBB region named PreA-Mar (http://preamar.io.usp.br/en). The results of Chapter 3 revealed that the Porto Channel behaves as a partially mixed estuary, being synchronous and tide-dominated, where tides propagate along the estuary mostly as a standing wave. In Chapter 4, the storm tides in the SSVBES were studied at both present and future conditions under two of the Intergovernmental Panel on Climate Change (IPCC) Representative Concentration Pathways (RCPs) scenarios for the end of the 21st century. The results showed that the storm tides in the SSVBES may increase in number but not in intensity, which may be comparable to the actual strengths. The sea level rise was the responsible for this conclusion whereas the expected changes in atmospheric circulation fields alone would produce less frequent and less intense storm tides.

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