An operational dynamical downscaling prediction system for Nordeste Brazil and the 2002-04 real-time forecast evaluation

The International Research Institute for Climate Prediction (IRI) and Ceara Foundation for Meteorology and Water Resources (FUNCEME) in Brazil have developed a dynamical downscaling prediction system for Northeast Brazil (the Nordeste) and have been issuing seasonal rainfall forecasts since December 2001. To the authors' knowledge, this is the first operational climate dynamical downscaling prediction system. The ECHAM4.5 AGCM and the NCEP Regional Spectral Model (RSM) are the core of this prediction system. This is a two-tiered prediction system. SST forecasts are produced first, which then serve as the lower boundary condition forcing for the ECHAM4.5 AGCM-NCEP RSM nested system. Hindcasts for January-June 1971-2000 with the nested model, using observed SSTs, provided estimates of model potential predictability and characteristics of the model climatology. During 2002-04, the overall rainfall forecast skill, measured by the ranked probability skill score (RPSS), is positive over a majority of the Nordeste. Higher skill is found for the March-May (MAM) and April-June (AMJ) seasons with forecast lead times up to 3 months. The skill of the downscaled forecasts is generally higher than that of the driving global model forecasts.