Fig. 1-4: The 30-day temperature and precipitation anomalies across South America plus the December (so far) deep layer soil moisture anomalies and the 15-day temperature forecast bias across South America by GFS ENS the past 30 days.
Discussion: During the past 30 days, temperature anomalies across Brazil have averaged 1.5C to 3.5C hotter than normal while the southern half of Argentina plus Chile are unusually cool (Fig. 1). The thermal pattern is inspired by a strong upper trough across southern portions of South America and an amplified upper ridge centered just off coastal Southeast Brazil. The rainfall pattern during the past 30 days is very wet in Southeast Brail/Northeast Argentina and Western Brazil while most of the remaining sections of Brazil are dry (Fig. 2). The influence of this regime plus the longer-term climate is to produce deep (10-200 CM) soil moisture anomaly deficits across Northern Brazil, Southwest Brazil, and Interior East Brazil (Fig. 3). These zones are highlighted for potential worsening drought during summer 2023-24. Western Brazil and a small narrow trajectory into Central Brazil have been wetter than normal and have near neutral deep layer soil moisture deficits. The Anomalous heat is certainly accelerating Brazil drought risk. However, be aware that forecast models (particularly GFS ENS) have been over forecasting anomalous heat in 15-day outlooks so far in the calendar summer season (Fig. 4).