Abstract
A new method to determine the onset dates of the rainy season (ONR) in the Central Amazon area using the antisymmetric in relation to the equator outgoing longwave radiation (OLR) data was developed in a previous paper. This method is adjusted and used here to determine the ONR in Western‐Central Brazil (WCB). The adjustment is needed because of the northwest‐southeast (NW‐SE) orientation of the American monsoon‐related convection displacement. The area averages of the OLR (AOLR) are used to identify the ONR dates. The ONR dates in WCB based on the precipitation index determined in a previous work are used as reference for comparisons. The differences between the results with the AOLR method and those shown in previous papers, as well as the advantages of this method are discussed, using composite maps of OLR and maps of the Tropical Rainfall Measuring Mission (TRMM) precipitation data for individual years. The results obtained here for the WCB indicate a potential of the new method for monitoring purposes because the OLR data can easily be obtained and the AOLR calculation is very simple. Copyright © 2011 Royal Meteorological Society