MJO East Shift Brings Wetter Bias to South America Last 1/3 of Month

Climate Impact Company Sunday AG Report

Global Weather/Climate Report

Issued: Sunday January 11, 2026

Highlight: MJO east shift brings wetter bias to South America last 1/3 of month.

Fig. 1-2: The precent normal rainfall observed for the week of January 3-9, 2026, and daily (NOAA/CPC) soil moisture anomalies analysis.

Discussion: During early January, the evolving wet zone across Brazil is the Interior Northeast most recently shifting toward the coast while evolving quickly across west/north sections of Argentina (Fig. 1). Dryness is exceptional across Paraguay and eastward plus coastal Northeast Brazil, east coastal and southern portions of Argentina. Soil moisture conditions reveal favorable conditions across Argentina while most of Brazil is in a dry-to-drought scenario (Fig. 2).

The convection phase of the Madden Julian oscillation (MJO) is moderately strong near the Dateline. Forecasts indicate an eastward shift toward the longitude of the Americas in the extended range. While the current (phase_6) of MJO favors a drier than normal climate for most of Argentina/Brazil, the shift into phase_7 favors broadly wetter than normal climate. Consequently, wetter 8-14/11-15-day (model) forecasts are favored. The wetter bias should last into the 16-20-day timeframe.

The 06Z GFS best captures the MJO-inspired regime of the next 2 weeks with a mostly drier than normal 7-day forecast shifting wetter in the 8-14-day period (Fig. 3-4). The anticipated wet bias lingering in the 16-20-day period is mostly across Brazil according to AI Graph Cast (Fig. 5).

Fig. 3-5: GFS 1-7-day and 8-14-day percent of normal rainfall forecast across South America plus the percent of normal rainfall outlook by the AI Graph Cast during the 16-20-day period.