The Earth＇s atmosphere is generally considered to be an example of a chaotic system that is sensitively dependent on initial conditions, It is shown here that certain regions of the atmosphere are an exception, Wind patterns and rainfall in certain regions of the tropics are so strongly determined by the temperature of the underlying sea surface that they do not show sensitive dependence on the initial conditions of the atmosphere. Therefore, it should be possible to predict the large-scale tropical circulation and rainfall for as Long as the ocean temperature can be predicted. If changes in tropical Pacific sea-surface temperature are quite Large, even the extratropical circulation over some regions, especially over the Pacific-North American sector, is predictable.