The purpose of this paper is to introduce and evaluate a high-resolution (5km) atmospheric downscaling system. The NCEP-NCAR Reanalysis and the NCEP-DOE Reanalysis II are used to drive a 30 years multi-scale simulation. We report in this paper the different steps for the implementation of the downscaling strategy. Our system has been applied to the east coast of South America with a specific emphasis put on Uruguay. We validate the results by carrying out a direct comparison with the available historical in situ observations. We show that our simulation develops a good representation of the seasonal and interannual variability for temperature and winds in the surface layer. The methodology presented here provides a basis for generalizing this approach to future studies especially for regions with a very limited observational network. Moreover we are on the path to include more precise informations about the sea-state by adding a wave model in our downscaling system.