South America Forecast Discussion - International Desks
NWS Weather Prediction Center College Park MD
341 PM EDT Wed Aug 26 2026

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

Forecast Bulletin 26 August 2026 at 1940 UTC:

Over the next three days, significant precipitation is expected
across the Chilean Andes as well as southeastern Brazil and
Uruguay. A low pressure system and its associated frontal
boundaries will transport deep moisture into central Chile, while
a separate frontal boundary lifting northward over northeastern
Argentina into Uruguay and southeastern Brazil will generate
widespread convective activity Thursday and Friday. North of 20S,
the pattern remains relatively quiet under broad high pressure.

Tropical South America (North of 20S):

The overall pattern across tropical South America is comparatively
benign through the forecast period. Upper-level winds remain weak,
and low-level flow across eastern Brazil is dominated by a surface
high pressure system, limiting large-scale forcing for
precipitation. However, moisture convergence across northwestern
South America will combine with diurnal heating to support
scattered shower and thunderstorm development, particularly during
the afternoon hours. These convective episodes are not expected to
be widespread or severe, and should remain tied to the daytime
heating cycle.

Chile and the Andes:

A low pressure system over the eastern Pacific will track toward
the Chilean coast, driving low-level moisture onshore into central
Chile. This moisture feed, combined with favorable mid- to
upper-level ventilation and orographic forcing along the Andes,
will sustain persistent and potentially heavy precipitation over
the Chilean cordillera through the forecast period. Significant
precipitation amounts are possible, especially across the higher
terrain.

Southeastern Brazil, Uruguay, and Northeastern Argentina:

A cold front advancing northward from southern Argentina into
northeastern Argentina will serve as the primary forcing mechanism
for convection across the region. Ahead of the front, a northerly
low-level jet will transport warm, moist tropical air southward,
pooling low-level moisture along and ahead of the frontal
boundary. This moisture convergence, combined with strong
mid-level winds and upper-level diffluence, will create an
environment highly conducive to thunderstorm development.
Instability generated by the combination of warm air advection
from the north and upper-level trough support will favor strong to
severe convection over southeastern Brazil and northern Uruguay on
Thursday and Friday. A moderate risk of severe weather is possible
for this area.


Alamo...(WPC)