South America Forecast Discussion - International Desks
NWS Weather Prediction Center College Park MD
305 PM EDT Tue Jun 09 2026

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

Forecast Bulletin 09 June 2026 at 1915 UTC:

A dynamic mid-to-upper level pattern will be present across Chile,
where a series of shortwave troughs will be traversing the region,
leading to the enhancement in divergence and vertical ascent,
particularly for Tuesday and Wednesday. At the surface, there will
be daily cold fronts moving into the continent. The first frontal
system is already moving into the continent and is being
accompanied by strong low level north-northeasterly wind speeds
and precipitable water values of 25mm. Moisture convergence will
be most enhanced during the morning and will decrease during the
day as the low level wind speeds decrease. Thus, moderate rain
accumulations are likely for austral and southern Chile for
Tuesday. The cold front will continue propagating northward on
Wednesday into southern Chile, where there will still be moist air
advection and surface convergence. Anticipate light accumulations
with these conditions on Wednesday for central Chile.

Also on Wednesday, expect elevated mid-to-upper level support as
an upper jet streak max, that will be perpendicular to the
continent, will be propagating inward and further elevating
divergence. Though the precipitable water values will be low,
expect strong onshore (westerly) low level wind flow into Los
Lagos, leading to localized regions of enhanced moisture
convergence. Meanwhile at the surface, a weak frontal boundary
will be moving into the austral Chile, leading to the enhancement
in surface convergence. Anticipate moderate total precipitation
maxima with these conditions in Los Lagos and Aysen for Wednesday.
For Thursday, yet another frontal boundary will be moving into
austral Chile, and precipitable water values will be limited but
the low level wind speeds will be strong. Moderate total
precipitation maxima are expected across the entire region for
this period.

Another region of interest is central South America. The remnants
of a surface front will begin to transition into a surface-to-low
level trough across Paraguay and southeast Brasil after Tuesday.
On Tuesday, a mid-level trough will also be propagating across
Paraguay and another one across Bolivia. These two regions will
also have moisture transport and upper level divergence that will
support light to moderate total precipitation maxima.


Also starting on Tuesday and continuing into Wednesday there will
be an increase in northerly low level winds in the region,
primarily being driven by the decrease in pressure values
associated with the arrival of an upper trough into the region.
The axis of the upper trough will extend into the southwest Amazon
and will support the development of a jet streak max along its
exit region, which will extend into Paraguay and southeast Brasil.
Another mid to upper level shortwave trough will be moving into
Paraguay and Bolivia on Thursday, leading again to the enhancement
of divergence in the region. A secondary mid-to-upper level
shortwave trough will arrive into Paraguay and will support the
development of a frontal boundary across Paraguay, southeast
Brasil, and Bolivia on Thursday. There will be moisture
convergence along the frontal boundary, being one of the
contributing factors to the development and sustenance of
precipitation along the boundary.

In the tropics, with the arrival of a mid-to-upper level trough
across the southwest and west Amazon Basin, there will be a
developing region of convergence in the region, where we will see
the confluence of easterly and westerly low level winds.
Precipitation accumulations will be elevated in this zone and
convection will be maintained by the presence of mid-to-upper
level divergence. Thereafter, westerly low level winds will begin
to dominate for Wednesday into Thursday, which will limit the
transport of moist tropical air into the western Amazon Basin.
Thus, there will be a reduction in precipitation accumulations in
the region and the precipitation that does develop will be more
surface to low level based.

Otherwise, the presence of low level troughs and tropical waves
will support precipitation processes for the next three days in
the region. In particular, there is a tropical wave that will be
moving across the Guianas during the day today and this wave will
continue moving across the northern regions of the continent.
Expect moderate to enhanced total precipitation maxima in the
vicinity of these features.

Tinoco-Morales...(WPC)