Unusually Warm Tropical Atlantic SSTA To Fuel A Wet Brazil Climate

A Wet Climate Is On The Way for Brazil Later This Year!

Fig. 1: The best initialization of current global SSTA conditions is provided by the International Multi-model Ensemble (IMME) which correctly identifies regional SSTA affecting South America climate.

Discussion: Brazil is in a long-term drought pattern. Generally, a La Nina pattern can bring widespread beneficial rainfall to Brazil especially northern areas. La Nina is now forecast to return by quarter 4 of 2021. Of interest, is the potential influence of very warm SSTA in the tropical Atlantic Ocean on the evolving La Nina climate later this year which could produce a wetter than normal La Nina pattern.

The best (model) initialization of global SSTA for July 2021 is by the International Multi-model Ensemble (IMME) which correctly identifies several regional SSTA patterns of importance to South America climate. ENSO is in neutral phase and the IMME model correctly identifies a small area of anomalous warm SSTA off the northwest coast of South America (Fig. 1). The model also correctly identifies a persistent plume of very warm SSTA in the central and east Atlantic tropics. Elsewhere in the tropics, evolution of a negative phase Indian Ocean Dipole (-IOD) is correctly identified by the IMME model. -IOD works with ENSO to affect the South America climate.

The interest here is whether the warm Atlantic tropics persists as La Nina develops in about 3 months. The IMME global SSTA forecast for October 2021 indicates the warm SSTA in the tropical Atlantic expands westward to the north/northeast South America coast (Fig. 2). Due to the proximity of this oceanic warmth to the equatorial East Pacific, the developing La Nina also shifts west toward the Dateline and a La Nina Modoki is born.

The cool waters of the central and east-central equatorial East Pacific are present due to La Nina-inspired stronger than normal trade winds which up-well cooler subsurface waters. Farther upstream, the trade winds pass over warmer than normal ocean water in the Atlantic tropics which sweeps abundant low atmospheric moisture into northern South America including much of Brazil. This scenario should cause a widening wet pattern in Brazil possibly beginning in September but certainly by October.

The International Research Institute for Climate and Society probability forecast for rainfall across South America valid SEP/OCT/NOV 2021 identifies the likely emerging wet pattern for Brazil (Fig. 3). IRI extends the wet pattern farther south during quarter 4 of 2021. The Climate Impact Company constructed analog forecast indicated patchy rainfall for Brazil (Fig. 4). The probabilistic forecast is likely more correct given the difficulty finding past years when the Atlantic tropics were so warm.

Bottom line? Drought relief for Brazil is on the way!

Fig. 2: The IMME global SSTA forecast for October 2021 indicates a west-biased La Nina evolution and a westward expansion of warm SSTA in the tropical Atlantic Ocean.

Fig. 3: The rainfall probability climate forecast across South America for SEP/OCT/NOV 2021 by the International Research Institute for Climate and Society.

Fig. 4: Climate Impact Company constructed analog rainfall forecast for SEP/OCT/NOV 2021 across South America.