The first operational version was implemented to forecast waves at Guaecá Beach, in São Sebastião. At that stage, the main objective was to test whether a high-resolution coastal grid could provide more useful local information than global wave models alone.

GUAECAST V1.0 used the SWAN model nested inside NOAA's WaveWatch III global forecast. The global model supplied offshore wave conditions and wind forcing, while the local SWAN grid represented the coastal transformation of waves near Guaecá and the surrounding São Sebastião/Ilhabela region.

This version also included astronomical tide information from the São Sebastião tide gauge, allowing water-level variations to be considered in shallow-water wave propagation. The model was operated mainly during the autumn and winter seasons, when larger swell events are more frequent and more relevant for surf forecasting.

The main lesson from V1.0 was that the nested approach worked. Even with a relatively limited domain, the higher-resolution model improved the ability to represent local effects caused by bathymetry, headlands, islands and shoreline geometry.

GUAECAST V2.0 expanded the system beyond its original single-beach focus. The forecast domain was extended to cover a larger portion of the São Paulo coast, including Santos, Guarujá, São Sebastião and Ubatuba. The name GUAECAST was retained because it had already become associated with the project.

To cover this larger region without losing local detail, the model was reorganized into a hierarchy of nested grids. A broad outer grid receives the offshore wave conditions, an intermediate grid resolves the central and northern São Paulo coast, and local grids provide higher-resolution results for the main forecast regions.

This multi-grid structure made it possible to keep computational costs reasonable while still resolving the nearshore areas where wave transformation is most important. The local grids were used to produce maps, time series and analysis products for specific beaches and coastal sectors.

During the V2.0 period, the system also became a year-round operational forecast. Updates to bathymetry, forcing datasets and model configuration were incorporated as new data and global model products became available.

GUAECAST V3.0 consolidated the current regional configuration and extended the forecast horizon to 14 days. This was possible because global wave forecast products evolved to provide longer outlooks, allowing GUAECAST to generate a two-week forecast while still preserving the local downscaling strategy.

The V3.0 configuration keeps the broad spatial coverage established in V2.0, with regional and local products for Baixada Santista, São Sebastião and Ubatuba. The main improvement is not a new geographic domain, but a more complete forecast window and a clearer set of products for interpretation.

Version 3.1 is an operational and visual update. On the data side, it adapts the processing workflow to changes in how NCEP makes the data available. Earlier versions accessed data through OPeNDAP, while the current operational workflow uses GRIB files. This change required adjustments in the data ingestion and preprocessing steps, but preserves the overall modeling approach.

On the website side, V3.1 reorganizes the forecast interface, improves mobile responsiveness, and modernizes the visual presentation of maps, charts and navigation. The goal is to make the forecast products easier to browse without reducing the technical content behind them.

The figures below show the current GUAECAST grid configuration. The broadest grid receives boundary conditions from the global model and passes the information to progressively finer grids. The local grids focus on the main forecast areas: Santos/Guarujá, São Sebastião and Ubatuba.

Figure 1: broadest GUAECAST grid, covering southern Rio de Janeiro and São Paulo. Open boundaries are indicated in red; the coarser grid represents the NOAA/EMC WaveWatch III global model.

Figure 2: intermediate GUAECAST grid, covering the central and northern coast of São Paulo.

Figure 3: local grids for Santos/Guarujá, São Sebastião and Ubatuba.

Figure 4: Santos/Guarujá local grid. Numbers indicate locations used for local forecast analysis.

Figure 5: São Sebastião local grid. Numbers indicate beaches and local analysis points.

Figure 6: Ubatuba local grid. Numbers indicate beaches and local analysis points.

Figure 7: comparison between the high-resolution GUAECAST grids and the WW3 global grid, highlighting the difference in spatial scale.