One of the main objectives of GATE was to study African wave disturbances and to learn more about their characteristics as they propagated westward from Africa across the eastern Atlantic Ocean. An important component of this objective was to document the background mean state in which these wave disturbances were embedded. It has long been recognized that Phase 3 of GATE (30 August - 19 September 1974) was the period during which convection and other properties of the flow associated with these disturbances were the most organized. With this in mind, the purpose of the present paper is to ascertain how anomalous the background conditions were during Phase 3 of GATE by providing a comparison of the mean states of the atmosphere between GATE analyses and a recent 15- year climatology for the Phase 3 period. The bulk of the results used to make this comparison come from the ECMWF Re-Analyses (ERA) based on the period, 1979-1993. Outgoing longwave radiation (OLR) is also used. Comparisons will be presented in map format, as well as in the form of vertical cross sections. Variables, in addition to OLR, that will be examined include streamlines and isotachs, the zonal wind component, relative vorticity, and vertical p- velocity. In a companion paper which follows (Fink, Vincent and Speth), some climatological aspects of the wave disturbances will be presented and compared to the waves that were documented during Phase 3 of GATE