696
FXUS20 KWBC 241657
PMDSA

South America Forecast Discussion - International Desks
NWS Weather Prediction Center College Park MD
1256 PM EDT Thu Sep 24 2026

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

Forecast Bulletin 24 September 2026 at 1755 UTC:

A dynamic upper level pattern will be affecting Chile for the next
three days. Today and Friday, expect the presence of an upper jet
streak max across south Chile that will also contain westerly low
level winds. This wind flow pattern will be orthogonal to the
local topography, which will also support an enhancement in upper
divergence. Though, the period with the greatest precipitation
impact is expected for today. A surface frontal boundary is
currently converging into south Chile and will move along the
Chilean coast for the next three days. The accompanying moisture
plume will begin to lose intensity as it shifts northward.Thus,
expect intense total precipitation maxima across south Chile
through Friday morning. A secondary cold front is approaching
Chile and is converging into southern Chile as well and is being
accompanied by a weaker moisture plume. Through Friday morning,
this secondary frontal boundary will support toilet precipitation
maxima of up to 50mm. For Friday and Saturday, a total
precipitation maxima of up to 35mm is likely across south Chile
(near Aysen and Los Lagos).

Also note that by Saturday, the upper level wind pattern will
shift as the axis of an upper level trough will begin to approach
the continent. Meanwhile in the subtropics, a mid-to-upper level
ridge will be moving in Bolivia and will begin to interact with
the aforementioned upper jet streak max across northern Argentina
and Uruguay for Saturday, leading to zone of speed divergence and
upper level shortwave troughs. Additionally, a frontal boundary
will be developing across north-central Argentina and there will
also be an increase in northerly low level winds; the low level
wind pattern will favor the transport of moist tropical air into
the mid-latitudes. Moisture convergence is anticipated along the
frontal boundary, sustaining elevated total precipitation maxima.
There will also be a risk for severe weather in the region.

Another region of interest in the subtropics is the southeast
Atlantic coast of Brasil (in the vicinity of Espirito Santo). A
stationary front, located near Espirito Santo, will begin to
weaken. As the frontal boundary weakens, expect the brief return
of easterly low level winds for Thursday and Friday. Showers and
thunderstorms are expected for this period with accumulations of
up to 20mm likely.

In the tropics, a tropical wave is continuing to move across the
north part of the continent and is expected to move across the
Colombia Andes on Saturday. Additionally, an upper level trough is
situated across northern Venezuela and it is supporting upper
divergence across the northwest Amazon and Venezuela. This upper
trough will meander in the region through the next three days. A
period of interest is for Saturday when upper diffluence will
become amplified across Venezuela and Colombia. The environment
will remain during the next three days as well. These conditions
will favor moderate to enhanced total precipitation maxima across
the aforementioned regions.

Along the Pacific coasts of Ecuador and Colombia, expect diurnal
convection and showers to continue through the next three days. As
the tropical wave moves west of the Andes, expect a resurgence in
westerly low level winds. This is also in response to the
development of another clockwise-rotating system off the coast of
Ecuador. Overall, the most elevated total precipitation maxima is
expected for Saturday.



Tinoco-Morales...(WPC)





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