South America Forecast Discussion - International Desks
NWS Weather Prediction Center College Park MD
254 PM EST Mon Nov 09 2026

GFS data at ftpprd.ncep.noaa.gov/data/nccf/com/gfs/prod/

Forecast Bulletin 09 November 2026 at 2000 UTC:

For the next three days, a broad upper level ridge, otherwise
known as the Bolivian High (BH), will be present across
tropical/subtropical South America. This upper level feature will
be driving convective initiation and sustenance through the week.
On Monday, the Bolivian high will be interacting with a
pre-existing upper level trough, located over northeast Brasil,
creating a region of speed divergence across central Brasil and
upper diffluence across north-central Brasil (east Amazon basin).
Additionally, there will be low level wind convergence (700 mb)
across southeast Brasil, leading to moisture pooling and the
enhancement in cyclonic circulation. Meanwhile, along the coast of
Espirito Santo/South Bahia, a frontal will also be present and
will remain in this region through the forecast cycle. This will
also lead to easterly low level winds moving onshore and thus
supporting additional moisture pooling along the local topography
and orographic enhancement.

With respect to precipitation, total precipitation maxima will be
elevated across the Cerrado region of Brasil for Monday in
alignment with the region of greatest upper level support. Across
central Brasil and the Amazon, expect moderate to enhanced total
precipitation maxima as well. Meanwhile across Bahia, the presence
of the surface front will lead to total precipitation maxima
exceeding 25mm daily.

By Tuesday, the upper level trough in northeast Brasil will begin
to lose its definition and the upper level ridge center will
reorganize farther west, across south Peru and west-central
Bolivia. This upper level ridging pattern will project into the
mid and low levels, leading the enhanced easterly winds across the
Amazon Basin. This pattern will help with moisture pooling across
the west Amazon Basin for Tuesday and Wednesday. Overall, expect
similar low-to-upper level wind flow patterns across the Amazon
for Tuesday and Wednesday where daily convection will support
total precipitation maxima of up to 25mm with isolated higher
accumulations likely.

On Wednesday, a mid-to-upper level trough will be moving across
Paraguay and Mato Grosso Sur. The region will have ample moisture
and instability, leading to the development of thunderstorms. A
surface low level trough will be developing, acting as the
catalyst for surface convergence. Moderate total precipitation
maxima is likely with these conditions in the region.

In the higher mid-latitudes, across Chile, expect the daily
traversal of frontal boundaries. These boundaries will be
accompanied with moisture plumes. The greatest precipitation
impacts are expected for Monday in austral Chile and central Chile
with the arrival of a mid-level trough. By Tuesday, another potent
mid-level trough with high vorticity will be moving into south
Chile, again leading to the increase in precipitation chances.
Total precipitation maxima will be elevated for both Monday and
Tuesday due to these conditions.

Tinoco-Morales...(WPC)