219
FXUS20 KWBC 251732
PMDSA

South America Forecast Discussion - International Desks
NWS Weather Prediction Center College Park MD
132 PM EDT Fri Sep 25 2026

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

Forecast Bulletin 25 September 2026 at 1800 UTC:

The upper-level pattern continues to be conducive for
precipitation over Chile, with strong winds aloft enhancing
upper-level divergence. Additionally, at lower levels the presence
of a frontal boundary and a plume of moisture will continue to
bring rainfall to the region. The highest accumulations are
expected today through Sunday, with totals ranging from 25-50mm
each day, for the Central Chile region. Then a decrease in
precipitation is expected as drier air is advected into the
region.

At low levels, strong northerly flow associated with low-level
jets advecting deep moisture from the tropics, alongside the
passage of a frontal boundary enhancing low-level wind
convergence, will promote heavy rainfall from Saturday through
Sunday over Uruguay, the Mesopotamia region of Argentina, and Rio
Grande do Sul in Brazil. Totals will range from 25-50mm. This
activity will continue and intensify from Sunday through Monday.
Additional support for thunderstorm development and convective
activity comes from upper-level divergence enhanced by upper-level
diffluence and strong winds aloft, as well as mid-level shortwave
troughs increasing instability. A moderate risk for severe weather
begins Saturday night.

A frontal boundary is expected to cross the Patagonia region from
Sunday through Monday, increasing low-level wind convergence.
This, along with upper-level divergence and strong winds aloft,
will bring precipitation particularly to Central Patagonia in
Argentina.

In the tropics, precipitation will mostly occur over the
northwestern portion of the continent, where moisture and
low-level winds converge. Daily rainfall is expected from today
through Monday along the Pacific coast of Ecuador due to the
advection of deep moisture from the Pacific by low-level
westerlies. Total rainfall is forecasted to range from 25-50mm
today through Saturday and from 35-70mm from Saturday through
Sunday. Another area of interest throughout the forecast period in
the tropics is the Amazon region, where low-level winds are
expected to converge and moisture will be advected into. A total
daily maxima of 20-40mm of rainfall is forecasted from today
through Sunday. Additional enhancement of precipitation in the
region is likely due to the presence and propagation of tropical
waves, low-level troughs, orographic lifting and diurnal heating.




Rivera-Torres...(WPC)





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