Eight frontal systems affected Brazil in January 1999. In the first fortnight of the month, frontal systems moved rapidly over the southern region and became nearly stationary over the southeastern characterizing the formation of the South Atlantic Convergence Zone (SACZ). Fast movement of the fronts in the southern region was related to rainfall deficit during the month. In the second half of the month the frontal systems were displaced to the Atlantic Ocean, causing little precipitation over the continent. In the Northeast of Brazil, upper level vortices were active in the first half of the month and as a result there was some precipitation over the northern coastal belt and the western parts of the region (Maranhão and Piauí). In the second half the vortices were positioned in the interior of the region, causing a reduction of rainfall in the whole region.

Negative anomalies of Sea Surface Temperatures between -1.5° C and -3.0° C were registered in the central and eastern Equatorial Pacific during the month. Similar anomalies were observed in the layers below the surface up to a depth of 300 m. The mean sea level pressure in the eastern South Pacific continued to be higher than normal in this month. The trade winds in the central and eastern Pacific continued to be stronger than normal. The Southern Oscillation Index (SOI) also continued to be positive for the nineth consecutive month. These three factors characterize a La Niña situation in its mature stage.

The SST observed over the Atlantic Ocean do not indicate any defined dipole situation (favorable or unfavorable for rain in the Northeast Brazil).

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