Shifting Madden Julian Oscillation, Wetter Brazil

Chart of the day: Eastward shifting MJO brings pattern change.

Discussion: The Madden Julian oscillation (MJO) is forecast to shift eastward from Maritime Continent (of the past several weeks) across the tropical East Pacific to tropical Africa over the next 2-3 weeks. The eastward shift should activate the North Atlantic tropics and increase risk of a wider wet weather pattern for Brazil.

Week-2 Valid September 29-October 5, 2024: VERY dynamic weather pattern across South America.

Discussion: Presence of MJO to the north and a fortified negative phase of the Antarctic oscillation (-AAO) set-up a dynamic weather pattern across South America. The MJO/-AAO combination could create a dry buffer between the wet tropics and stormy trough across Argentina OR the -AAO-induced trough over Argentina draws tropical moisture southward causing wet weather across Brazil. Option 2 is the likely trend. Consequently, the drought area in Brazil receives beneficial rainfall. The -AAO pattern delivers a cool air mass to Argentina.

Week-3 Valid October 6-12, 2024: Wet pattern in Brazil eases.

Discussion: The wet influence of MJO eases although residual showers remain across Interior Brazil.

Week-4 Valid October 13-19, 2024: Most of Brazil is hot and dry again.

Discussion: Persistence returns as Brazil observes widening anomalous heat and dryness.