The semi-permanent Amundsen Sea low pressure area emits low-pressure systems northeastward in the current weather pattern. The low-pressure systems are unusually strong featuring 970-980 MB low pressure. Attendant cold fronts extend to Southeast Brazil from these storm systems triggering heavy rains for that region in November.

As October 2023 closes, several climate diagnostics are notable. First, a marginally supportive of El Nino climate signature by the southern oscillation index has weakened. Second, snow cover in the northern hemisphere is ahead of schedule. Third, the marine heat wave in the Northeast Pacific has not progressed to the West Coast of North America to further enhance El Nino. Finally, an impressive +IOD pattern has emerged.

During AUG/SEP/OCT 2023, the Amundsen Sea low has disappeared and been replaced by an upper ridge. The presence of the Amundsen Sea low (since 2016) and isolated disruption (2019 and 2023) seems to be independent of ENSO phase. The effect of this regime on Brazil rainfall for AUG/SEP/OCT is generally wetter than normal. However, during the past 3 months, Central Brazil is notably dry while rainfall has consolidated mostly in East/Southeast Brazil.

As a reminder, the long-term ENSO cycle shifted to La Nina in the late 1990’s and has remained in-place through 2022. An El Nino has formed in 2023 but is not anticipated as a sign of ending the long-term cold ENSO cycle. The long-term cold ENSO cycle has produced a drier climate change across Brazil leading to higher susceptibility of drought and flash drought plus lowering river levels.