Madden Julian Oscillation Intensifies; Increased IO/WP TC’s, Wetter Australia, and Drier South America
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Tropical Storm Melissa Remains a RI Candidate
10/23/2025, 9:07 am EDT
Climate Impact Company Week 2-to-4 South America Outlook
Issued: Tuesday October 21, 2025
Headline: Cool air masses and wetter Brazil early November.
Charts of the day: The 5-day rainfall forecast and soil moisture update.
Discussion: A cold front pushes heavy rain into northeastern Brazil with a trailing cool air mass into midweek while a narrow high-pressure area heats Argentina midweek. Late week/early weekend brings a strong cold front with heavy rain to Northeast Argentina. Soil moisture conditions across South America continue to favor a long-term drought across much of Brazil with near to wetter than normal soils in Argentina.
Week-2 Valid October 26-November 2, 2025: Much cooler Argentina.
Discussion: The cold front moving through Argentina this weekend delivers a cool air mass lasting much of next week. The edge of the cooler air mass is where rainfall occurs, mostly east of Paraguay. Most of the Brazil drought area is warmer/drier than normal.
Week-3 Valid November 2-9, 2025: Confidence increases…wetter Brazil.
Discussion: The upper trough delivering the cool air mass to Argentina during late October cuts off from the main circulation and rests over central South America during the first full week of November. The upper trough produces a wet pattern change in Brazil. ECM and AI models are agreeable to the trough position.
Week-4 Valid November 9-16, 2025: Hotter/drier Argentina.
Discussion: Argentina turns hotter and is mostly dry while Brazil is normally hot and showery East.