Six frontal system affected Brazil in the month of May 1999. This number is very close to the climatological mean. These systems in association with the upper level cyclonic vortices were responsible for the positive rainfall anomalies and strong winds in South Brazil. One of the systems caused snowfall in the uplands of Rio Grande do Sul and in São Joaquim (SC). Rough sea and high waves were observed in the coastal sea of Rio Grande do Sul, São Paulo e Rio de Janeiro. First forest fire spots were observed in Central Brazil favored by the reduction of rainfall in this month.

The oceanic conditions in the equatorial Pacific continued to indicate the La Niña phenomenon, however with less intensity than in the months of March and April. The wind and pressure patterns were typical of the La Niña situation. Some positive SST anomalies were observed in the Indonesian sea.

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