BRAMS (Brazilian developments of the Regional Atmospheric Modeling System) is a mesoscale model for weather predition. In the Center of Weather Predition and Climate Studied (CPTEC), a division of the National Institute for Space Research (INPE), BRAMS was also adapted to be used as an environmental prediction model. The CPTEC-INPE has employed the BRAMS as an operational tool to provide the forecasting to the pollutant gases, including chemical reaction, over the Brazilian region. Recently, an effort to apply the third order Runge-Kutta (RK3) as a new dynamical core for the BRAMS model version 5.2. In this paper, the development of the parallel version of the RK3 is described. The new dynamical core for the BRAMS is evaluated simulating events under strong rain-fall in different regions of the Brazil.