362
FXUS20 KWBC 031853
PMDSA

South America Forecast Discussion - International Desks
NWS Weather Prediction Center College Park MD
253 PM EDT Thu Sep 03 2026

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

Forecast Bulletin 03 September 2026 at 1900 UTC:

Over the past few days, the continent has seen a shift in overall
precipitation pattern, where the Subtropical Ridge is located over
the continent, extending as far south as the Chaco region, and as
far east as central Brasil on Thursday morning, meandering from
the east Pacific earlier in the week. To its south, the
Subtropical Jet and North Polar Jet in the upper levels extend
from central Chile, through Argentina and into Uruguay and south
Brasil, where the divergent exit region favors a strengthening of
the extratropical sys tem over the south Atlantic Ocean. The
system has a frontal boundary in the lower levels that enters
Uruguay/Rio Grande do Sul-Brasil and into northern Argentina by
Thursday morning. Favored by the presence of the upper level jets,
the frontal boundary will continue a northward movement, and it is
expected into the Chaco region in Argentina, and exiting along the
Santa Catarina/Rio Grande do Sul region in Brasil by Thursday
evening. In terms of precipitation, expect light to moderate
precipitation totals as front propagates northward quickly and the
amount of available moisutre decreases into the early hours of
Friday in south Brasil, where they can also expect a slight risk
of severe weather. On Friday, the frontal boundary is expected to
enter south Bolivia, Paraguay, and meander over south Brasil
before exiting into the south Alantic Ocean. While that continues
to enter the region, expect the South Americal Low Level Jet
(SALLJ) to advect moisture from the tropical north, converging
with the frontal system. This will favor precipitation from south
Paraguay to the Serra do Mar region of Brasil. Expect moderate
accumulations, with a slight risk of severe weather. To the north,
the upper level ridge is expected to meander eastward over east
Brasil by Friday evening, with its periphery over the eastern
Amazon Basin, where expect moist plumes to propagate from the east
over the region. Diurnal heating will favor convection and the
upper level divergence along the periphery of the upper level
ridge will enhance lift over the region. Although total
precipitation is not expected to be heavy, the region has been
seeing dry conditions. This will beging to change the pattern and
bring some precipitation. On Sunday, the the eastward positioning
of the ridge will allow for upper level troughing to take place
over the western Amazon Basin, and give way to the northward
propagation of the frontal system into north Bolivia and Mato
Grosso, exiting into the Atlantic Ocean from Rio de Janeiro by
Saturday evening. A potential for a shear line to develop ahead of
the front over central Brasil is possible as this system
propagates quickly to the north. Expect the heaviest
precipitations over the foothilsl of the Andes in southern peru
and central Bolivia, while south Parana and Santa Catariba can
expect moderate to heavy precipitation on Saturday.

Castellanos...(WPC)





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