The East Atlantic/Western Russia (EAWR) index is present when a strong trough is located across Europe and north of China while amplified high pressure zones occupy the central North Atlantic and Caspian Sea region. In this pattern, which developed over 1 week ago and is forecast to remain through the next 2 weeks, heavy precipitation stretches across Europe.

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During AUG/SEP/OCT 2023, the Amundsen Sea low has disappeared and been replaced by an upper ridge.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.