NCEP CFS V2 Opinion of South America Climate for NOV/DEC 2021

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Highlight: NCEP CFS V2 forecasts a wet Brazil/dry East Argentina to far Southeast Brazil November/December.

Fig. 1: NCEP CFS V2 upper air forecast for November 2021 across South America.

Discussion: The NCEP CFS V2 offers clues as to the prevailing climate pattern across Brazil and Argentina into early meteorological summer. The November upper air forecast indicates a semi-permanent upper trough due east of Uruguay (Fig. 1). Forecast confidence is above average due to the reginal cool SSTA pattern is this location. Farther south where a large region of warm SSTA is located to the east of Argentina, an upper-level high-pressure ridge is likely to dominate stretching westward across Southern Chile. The sensible weather induced by these upper air features is a wet return-flow from the warmer-than-normal South Atlantic tropics across much of Brazil sustaining the already wet spring climate. However, just-north of the South America high-pressure ridge, a north to west land breeze prevails leaving the north/east Argentina to far Southeast Brazil climate pattern dry.

Fig. 2: NCEP CFS V2 upper air forecast for December 2021 across South America.

In December, the upper-level ridge pattern splits with one center west of Chile and another east of Argentina (Fig. 2). In-between a weak upper trough pattern prevails. The upper-level split in the ridge pattern by the NCEP CFS V2 model is due to the expected emergence of warmer SSTA west-southwest of Chile and a slight-eastward shift of the warm SSTA off Argentina as indicated by the International Multi-Model Ensemble global SSTA forecast (Fig. 3).

In December, the sensible weather pattern favors more wet weather in Brazil although the amplitude of the wet signal may ease later month as the aerial coverage and intensity of the warm SSTA in the South Atlantic tropics is easing. Western Argentina is susceptible to thundershowers but eastern sections to southeast Brazil are likely drier-than-normal during early summer.

Drought conditions in northeast, central and south-central Brazil continue to fade in a wet climate pattern. Areas of excessive soil moisture could develop by early summer. However, just-the-opposite regime is possible just to the south including far southeast Brazil, southeast Paraguay, north and northeast Argentina and Uruguay where a drought watch is in-place.

Fig. 3: The IMME global SSTA forecast for December 2021.