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FXUS20 KWBC 281926
PMDSA

South America Forecast Discussion - International Desks
NWS Weather Prediction Center College Park MD
326 PM EDT Fri Aug 28 2026

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

Forecast Bulletin 28 August 2026 at 1920 UTC:

At the upper levels, a trough sits over the southwest Atlantic,
just east of southeast Brazil. The flow is mostly west-to-east
across the continent south of 20S, with a broad trough stretching
from eastern Bolivia into western Brazil. A jet stream runs across
central Chile into northern Argentina and Uruguay. This pattern
will hold through the weekend.

At the mid levels, high pressure covers north-central South
America, just north of 20S. South of there, a jet stream sits near
30S, with westerly flow continuing across the continent into the
Southern Cone. On top of that, a low pressure system with a trough
will move into the Southern Cone from the Pacific on Sunday.

At the lower levels, a low-level jet from the northwest will push
across Bolivia into southeast Brazil today (Friday) into Saturday,
with weaker winds but still a northwest flow on Sunday. This
northwest flow will bring a steady supply of moisture into the
area. Broad high pressure will settle over much of the continent
north of 20S and stick around, keeping that region drier than
normal. In the Southern Cone, a couple of weak lows and troughs
will move through over the weekend.

Over the next three days, a slow-moving front across southeast
Brazil will keep interacting with the low-level moisture over the
area just ahead of it. There will also be mid and upper level
support from the strong winds at those levels. The mix of the
moisture pooling ahead of the front and the strong winds aloft
will bring a slight to moderate risk of strong thunderstorms each
day across southeast Brazil, close to the northern border of
Uruguay. The latest satellite imagery shows a narrow but steady
line of storms across the region. That said, model guidance has
been inconsistent, and not in great agreement, with big
differences in both how much rain falls and where the heaviest
rain sets up. For that reason, the forecast uses a wider area for
significant rainfall while flagging the risk of severe weather.


Alamo...(WPC)





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