Precipitation characteristics in the Northeast Brazil dry region

The general meteorological conditions and precipitation characteristics in the Northeast Brazil dry region during its rainy season from December through April are discussed. It is found that most of the yearly rainfall comes in six to eight episodes from organized weather systems which move from east to west with about the same speed (∼5 m s −1 ) as the lower tropospheric wind flow. These systems appear not to be of local origin. Rainfall is shown to be inversely correlated with the regional subsidence. An interesting and previously unknown diurnal rainfall variation is found. Orographic influences appear to act to modulate the weather systems and develop upslope and downslope winds. This produces rainfall in the morning over the lowland regions and in the afternoon over the hills and more elevated regions. Extensive comparisons of the rain systems with other tropical regions are made. Other characteristics are discussed.