Influence on South America Climate of the Coastal Brazil Upper-level Low-pressure Area

Climate Impact Company AG Hot Spot

Issued: Monday October 6, 2025

Highlight: Influence on South America climate of the Coastal Brazil upper-level low pressure area.

Discussion: Important as a review, is the influence on summertime rainfall patterns in South America by a semi-permanent upper-level low pressure trough located off the Southeast coast of Brazil for most years in this decade. The just-issued ECMWF “monthlies” are forecasting the presence of this low-pressure system for early-to-middle summer (Fig. 1). The upper low is well-correlated to a persistent sea surface temperature anomaly (SSTA) pattern featuring a marine heat wave (MHW) off the coast of Argentina which is associated with anomalous high pressure aloft and compensated for by low pressure off the Brazil Coast. NCEP CFS V2 maintains the MHW east of Argentina for the summer season ahead (Fig. 2). The upper low is forecast by ECMWF for NOV/DEC/JAN 2025-26 similar with most years of this decade (Fig. 3). The attendant rainfall pattern features wet weather in East Brazil compensated for a drier than normal climate for southwest and southeast Brazil to Northeast Argentina (Fig. 4). Implied is some relief for the East-central/East Brazil drought zone while drought focus may shift southwestward toward Argentina by mid-summer.

Fig. 1-2: ECMWF “monthlies” project an upper-level low for early summertime off the Southeast Brazil Coast. NCEP CFS V2 projects continued presence of a marine heat wave off the Argentina Coast related to the upper trough forecast.

Fig. 3-4: During this decade, presence of the marine heat wave off the Argentina Coast is well-correlated to high pressure and a compensating low pressure to the north off the Brazil Coast causal to East Brazil summertime heavy rains.