Systematic forecast error associated with active episodes of the tropical Madden-Julian oscillation (MJO) is examined using 5 years of dynamical extended range forecasts from the National Centers for Environmental Prediction (NCEP) reanalysis model. Active episodes of the MJO are identified based on significant projection of observed outgoing longwave radiation, which is a proxy for tropical convection, onto the leading two empirical orthogonal functions that depict the MJO. Forecasts initialized during active episodes of the MJO are found not to capture the eastward propagation of the tropical precipitation and circulation anomalies associated with the MJO. Rather, the MJO-induced anomalies of precipitation and winds are forecast to systematically weaken and even retrograde. These systematic errors in the Tropics fully develop by about 7-10 days and are generally opposite to, but with the same amplitude as, the observed composite anomalies for the MJO. An associated systematic error of the extratropical 200 mb streamfunction also fully develops by about 7-10 days and is also generally opposite the observed composite streamfunction anomalies produced by the MJO. The development of the extratropical streamfunction error is argued to result from the error of tropical divergence forcing and, thus, the improper Rossby wave source as the MJO evolves.
Based on the strucuture of the systematic forecasts error in the NCEP model, an empirical prediction scheme for the MJO is developed using lagged-regressions of the leading principal components of OLR. This empirical prediction is shown to have skill out to about week 3. The scheme was developed based on 5 day running mean OLR anomalies (seasonal cycle and ENSO signals removed) and thus can be implemented in real time.