The 30-60 day Madden and Julian Oscillation is studied by analyzing satellite-derived outgoing longwave radiation (OLR) and precipitable water (PW) data, and 54 years of NCEP reanalysis upward longwave radiation fluxes. Zonal space-time spectral analysis and Fourier filtering is applied these datasets. These analyses reveal that disturbances forced by the MJO cluster in time and space in groups of up to around ten significant half cycles. Further, enhanced convection events are frequently followed by other enhanced events that reach their highest amplitudes to the west of where preceeding events reached their peaks. The result is an apparent westward group velocity. This behavior is confirmed using unfiltered data smoothed with a centered moving average. A statistical climatology of MJO groups is presented, covering the period from January 1, 1988 to December 31, 1997.