The Center for Weather Forecast and Climate Studies from the National Institute for Space Research (CPTEC/INPE; that is, a Brazilian National Weather Center) has been using a Physical-Space Statistical Analysis (PSAS) in its operational data assimilation system since 2004. Efforts are presently on the way to complete development and testing of a Local Ensemble Transform Kalman Filter (LETKF) as a replacement for PSAS. One feature of interest, to be added to the CPTEC implementation of the LETKF, is the capability to evaluation observation impacts. The present work outlines the effort under way to implement an observation impact tool following the approach of Liu and Kalnay (2008; QJRMS, 134, 1327-1355). This presentation will discuss practical aspects of implementation, including the strategy of re-computation. Furthermore, the presentation will show preliminary results of the observation impacts using the set of conventional observations currently available in the CPTEC LETKF.