Record-strength El Nino Ahead and Climate Influences of Other Strong Regional SSTA Patterns
09/01/2026, 4:40 am EDT
Climate Impact Company Week 2-4 Outlook
South America
Issued: Friday September 4, 2026
Highlight: Negative Antarctic oscillation (-AAO) and marine heatwave east of Brazil combine to produce a wetter regime East/Southeast Brazil.
Admin: Due to Super El Nino, Climate Impact Company issues week 2-4 and medium-range forecasts for South America 2-3 times/week beginning next week.
Charts of the day: Recent rainfall and 10-day outlook.
Discussion: ECMWF did a nice job forecasting expanding wet weather in Southeast/East Brazil for the past week. During that time, patchy rains remained in Argentina. ECMWF remains the wettest forecast model during the next 10 days although GFS is trending wetter. Combing the 2 models yields a very wet Southeast/East Brazil regime into mid-September.
Week-2 Ahead (September 13-20, 2026): -AAO inspires coastal low-pressure trough inviting East Brazil rains.
Discussion: ECMWF is most aggressive with the ongoing rains in Southeast/East Brazil. The outlook is supported by ongoing negative Antarctic oscillation (-AAO) which implies semi-permanent low-pressure troughs in the middle latitudes. ECMWF projects a semi-permanent low-pressure trough east of Argentina located across an area of relative cool SSTA. Meanwhile, east of Brazil, a marine heat wave (MHW) is expected to strengthen. The upper trough entrains increased low-level atmosphere moisture across the MHW driving a wetter Southeast/East Brazil climate likely to last through spring.
Week-3 Ahead (September 20-27, 2026): Staying wet Southeast/East Brazil.
Discussion: The set-up described, -AAO trough east of Argentina and MHW east of Brazil, sustains wet risk in East Brazil. In this pattern, dry El Nino-inspired weather is pushed farther westward in Brazil.
Week-4 Ahead (September 27-October 4, 2026): Argentina weather is quiet.
Discussion: While East/Southeast Brazil are wet, the Argentina weather pattern is generally normally wet or drier than normal with near to slightly below normal temperature.