492
FXUS20 KWBC 291906
PMDSA

South America Forecast Discussion - International Desks
NWS Weather Prediction Center College Park MD
305 PM EDT Thu Oct 29 2026

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

Forecast Bulletin 2 October 2026 at 1930 UTC:

Precipitation chances are expected to be elevated today from the
Cerrado through Espirito Santo/north Serra do Mar, being supported
by a dynamic low-to-upper level regime. The axis of an upper level
trough will be moving east of the Bolivian Andes this morning and
is expected to lose its definition as it continues moving into
Brasil through the day. This trough will be interacting with a
pre-existing upper ridge that will also have a center off the
coast of Bahia, leading to the development of speed divergence
across the Cerrado. Additionally, the low-to-mid level winds will
be converging overhead, leading to the support for ascent and
moisture pooling. Total precipitation maxima will range from 15 to
30mm across this region through Friday morning. Meanwhile across
Espirito Santo, in addition to the aforementioned conditions, a
surface warm front will also be developing along the coast and
moisture convergence will be magnified, particularly due to the
influx of northeasterly low level winds into the region. Total
precipitation maxima will be in excess of 50mm through Friday
morning.

To the south, expect the development of a low level trough across
south Brasil. A broad cyclonic low level wind flow pattern will
also be present for today through Saturday morning. Another low
level trough will be developing over Espirito Santo for Saturday
and will again increase moisture convergence in this region. This
system will support daily total precipitation maxima of up to
30mm. Note that by Saturday, moisture convergence is expected to
weaken across south and central Brasil with the change in low
level wind regime.

Meanwhile across Mato Grosso, precipitation chances are expected
to increase for Friday and Saturday as moisture convergence
increases in this region with the development of a low level
trough. Daily precipitation accumulations for these two days will
reach 20mm. Upper level jet dynamics will help keep the
environment unstable and will be conducive to upper divergence.

Across the west Amazon Basin, there will still be ongoing moisture
pooling along the Andes through the next three days. Though, the
central and west Amazon Basin will begin to see a substantial
increase in precipitable water values by Saturday as easterly
mid-level winds will return to the region, helping transport moist
air into the higher terrain of Ecuador and Peru. Precipitation
will stay confined to the westernmost extent of the Amazon and
expand to the east by Saturday with the increase of instability in
the region.

On the Pacific side, a low level convergence will be present
across south Colombia and Ecuador, leading to the enhanced risk
for convective initiation. Additionally, the environment is
already unstable and very moist, which will favor higher total
precipitation accumulations. By Saturday, mid-level convergence
will be increasing in the region, leading to the enhancement in
vorticity in the region and thus the initiation of convection. The
environment will remain unstable and moist, ample for higher
accumulations.

Across Argentina, a mid-level trough will be present across Rio de
la Plata and Buenos Aires. It is expected to develop into the
low-levels, which will be where precipitation will be developing.
Additionally, the very cold mid-level temperatures will favor
strong lapse rates and thus support severe weather. These
conditions will persist into Friday. The mid-level trough will
begin to move eastward thereafter. On Saturday, a mid-to-upper
level trough will be moving into north-central Argentina, leading
to the development of a frontal boundary and multiple low level
troughs. At the same time, there will be a surge in northerly low
level winds that will help moisten the environment. These
conditions will favor the initiation of precipitation across
north-central Argentina, where a total precipitation maxima of 20
- 40mm is likely across Cordoba.

In Chile, a series of frontal boundaries will be moving into
austral and southern Chile for the next three days, being
accompanied by moisture plumes and favorable upper level dynamics.
These transient systems will be favoring total precipitation
maxima of up to 40mm across the region for the next three days.
Mountain snow is likely as well.

Tinoco-Morales...(WPC)



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