12Z GFS South America Forecast is Wetter Central Brazil

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Highlight: 12Z GFS South America forecast is wetter in Central Brazil.

Fig. 1-3: The GFS 1-5-day temperature anomaly forecast, and medium-range 24-hour rainfall change projection across South America.

Discussion: The 12Z GFS indicates a split in the subtropical ridge during the medium range. Prior to that event, the upper ridge spawns a hot and dry forecast for Brazil valid this week (Fig. 1). However, the subtropical ridge over Southeast Brazil edges eastward in the 6-10-day period which allows a moisture feed from the deep tropics into central continent and a wetter forecast change (Fig. 2). Similarly, a tropical air mass trajectory yields a wetter forecast chance sine yesterday for west/southwest Brazil (Fig. 3).