The principal aspect observed in April 2004 was the above normal rainfall in parts of South Brazil and in southern portions of Mato Grosso do Sul, occuring after a prolonged deficit of rainfall for three consecutive months. The frontal systems during this month moved northward up to Southeast Brazil and one of them reached the equatorial region of Brazil. The occurrence of upper troughs and cyclonic vortices contributed for above normal precipitation in many parts of Southeast Brazil. The shortage of rainfall in the eastern sector of Northeast Brazil during the beginning of the rainy season was noteworthy.

Four cold air mass invasions during the month were responsible for periodically declining the temperatures in several regions of Brazill. However, the maximum and minimum daily temperatures remained above the historical means in almost the whole country.

In general there was reduction in river flow compared to the previous month (March), with negative anomalies in relation to the MLT in the southern parts of the Paraná River Basin, in the Southeast Atlantic Basin and in the Uruguay River Basin.

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