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FXUS20 KWBC 031728
PMDSA

South America Forecast Discussion - International Desks
NWS Weather Prediction Center College Park MD
1228 PM EST Tue Nov 03 2026

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

Forecast Bulletin 03 November 2026 at 1730 UTC:

In tropical South America...
A broad upper level ridge will be present across southwest Amazon
for the next three days, intensifying in definition with passing
days. Additionally, a mid-level ridge will also be reflected in
the region, which will promote the enhancement in low-to-mid level
easterly winds into the eastern foothills of the Ecuadorian and
Peruvian Andes. Moisture pooling is anticipated with this pattern
and orographic enhancement. Thus, expect the daily development of
convection and showers across this region through the forecast
cycle.

Meanwhile along the Pacific coast of Colombia, Ecuador, and Peru,
expect ample moisture and instability for the next three days.
Starting on Wednesday, a broad low level cyclonic circulation will
be developing off the coast of Ecuador, leading to the enhancement
in westerly and northwesterly winds into the coast. This, coupled
with local and orographic effects will lead to the sustenance of
convection in the region. Thus, expect daily total precipitation
maxima to reach 50mm at a minimum.

In the mid-latitudes...
The first area of interest in south Brasil and Uruguay for
Tuesday. There will be two separate mid-level troughs moving over
these regions, generating vorticity and cyclonic circulation.
Additionally, expect the presence of upper divergence overhead.
This divergence is being supported by the presence of upper level
diffluence being generated from the interaction of a weakening
upper trough and the aforementioned subtropical ridge. During the
day Tuesday, northerly low level winds will also be dominating the
region, extending into north-central Argentina. As a propagating
low level trough and surface frontal boundary develop over
Uruguay, north Argentina, south Brasil, expect the increase in
moisture pooling along these boundaries. The combination of these
conditions will lead to elevated total precipitation maxima for
Tuesday, particularly for Uruguay and south Brasil. There will
also be a risk for severe weather.

By Wednesday, the frontal boundary and low level trough will be
gaining latitude, moving into south Brasil, Paraguay, and Bolivia.
Moisture pooling will still be amplified along the boundaries. In
the upper levels, a potent and strengthening zonal jet streak max
will be developing overhead, helping support the development of
more mid-level shortwave troughs. Again, these conditions will
favor elevated total precipitation maxima with a risk for severe
weather. The area of greatest precipitation impact will be across
south Brasil where upper level divergence will be most magnified.
Total precipitation maxima for Wednesday will approach 125mm. An
additional precipitation maxima is expected across central Bolivia
on Wednesday, primarily due to the arrival of the propagating low
level trough and the convergence of the low level winds. By
Thursday, the rainfall maxima will shift northward with the
northward propagation of the surface frontal boundary along the
coastline. Total precipitation maxima of up to 35mm is still
likely across Rio de Janeiro. Meanwhile, for the next three days,
expect the daily development of showers and thunderstorms across
central Brasil that is being driven by the presence of an upper
level trough, whose axis is to the northeast. The region will
remain moist and unstable, favoring moderate total precipitation
maxima.

A series of upper level troughs will be moving across central
Argentina and Chile for the next three days. On Tuesday, a well
defined mid-level trough will be moving into austral Chile and
crossing into Argentina by Tuesday night. On the Chilean side, the
system will be accompanied with a weakening surface frontal
boundary. On the Argentinian side, expect the development of a low
level trough across the region. Additionally, the presence of
northerly low level winds into the region is helping moisten the
environment and thus lead to the presence of higher precipitable
water values. These two regions will receive total precipitation
maxima of up to 30mm for Tuesday.

By Wednesday, the mid-level trough will be exiting the region and
remnant rain showers and thunderstorms will be present in the
morning across Rio de la Plata and Buenos Aires/La Pampa. On the
Chilean side, another mid-to-upper level trough will be arriving
into the continent and it will be accompanied with a frontal
boundary with a more intense moisture plume. This surface system
will converge into the continent and support elevated total
precipitation maxima for Wednesday. On Thursday, the mid-to-upper
level trough will be moving east of the Andes and it will begin to
develop a low level trough across central Argentina. Precipitation
chances are expected to increase with the intensification of this
surface system.

Tinoco-Morales...(WPC)



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