851
FXUS20 KWBC 081612
PMDSA

South America Forecast Discussion - International Desks
NWS Weather Prediction Center College Park MD
1212 PM EDT Fri May 08 2026

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

Forecast Bulletin 08 May 2026 at 1618 UTC:

An upper level trough is currently situated across central South
America and it will continue to support a surface frontal boundary
across the subtropics. On Friday, a cold front will be across
Serra do Mar, Parana and Pantanal regions of Brasil and
Chiquitania in Bolivia. By Saturday evening, the front will be
across the southwest Amazon, southwest Mato Grosso, Pantanal,
Parana, and the Serra do Mar regions of Brasil. On Sunday, the
front will remain in the same regions but will gain latitude
compared to the day prior. Note that this cold front will be
approaching 6S in Peru by the end of the day Sunday. The front
will lose its structure as it continues to move into the western
Amazon basin on Sunday and Monday, though its remnants and
accompanying dry air advection will continue to move into the
Ecuador and southern Colombia after Sunday. A shear line will also
be developing across the central Amazon Basin on Sunday and it
will continue to extend into the Brasilian state of Amazonia by
the end of the day. The shear line will remain in the region for
Monday.

In the upper levels, across southeast Brasil, expect amplified
upper divergence. This divergence will be sustained by the
presence of a jet streak max and diffluence in the wind field.
After Sunday morning, the axis of the upper level trough will be
moving out of the continent, leading to a decrease in upper
divergence, though, there will still be mid-level divergence
present across Serra do Mar through Monday morning. In the low
levels, the South American Low Level Jet (SALLJ) will still be
present on Friday but it is anticipated to weaken thereafter. This
will lead to the decrease in moisture transport from the deep
tropics into the interior of Brasil. Though, there will be some
low-to-mid level confluence that will support moisture pooling
along the boundary in Brasil. Thus, for Friday and Saturday,
expect enhanced total precipitation maxima across southeast Brasil
and Mato Grosso Sur.

Meanwhile across central Bolivia, enhanced north-northwesterly
winds will be converging into the area, leading to an increase in
moisture convergence along the frontal boundary. In the upper
levels, an inverted upper trough will be moving into the southeast
Amazon on Friday. This trough will support a diffluent wind
pattern across northern Bolivia and the south jungle of Peru for
Friday, promoting upper divergence. The highest accumulations will
be located southeast Peru and north-central Bolivia, where
enhanced total precipitation maxima is anticipated. By Saturday,
with the northward progression of the cold front, expect the low
level winds to become more easterly. This will lead to the
increase in moisture across the southwest and west Amazon, which
will extend into the high terrain. The areas with the greatest
precipitation impacts will be in the vicinity of the cold front.
Meanwhile, expect an increase in total precipitation maxima across
the western Amazon Basin as well. On Sunday, the area of greatest
precipitation impact will be the western Amazon Basin, where
elevated total precipitation maxima are likely. In the upper
levels, expect the increase in upper level divergence, which will
be attributed to a diffluent upper level wind pattern in the
region and an increase in upper level wind speeds. In the
low-to-mid levels, there will be an increase in easterly winds,
which will favor the transport of moist air. Thus, elevated total
precipitation maxima is likely across northern Peru and eastern
Ecuador for Sunday.

Elsewhere in the tropics, expect the presence and propagation of
low level troughs across the basin. These features will support
the enhancement in moisture convergence and cyclonic rotation,
yielding moderate total precipitation maxima in their vicinity.
Across the Amazon Delta and northeast Brasil, the presence of the
Intertropical Convergence Zone (ITCZ) will continue to assist in
the transport of moist Atlantic air into the region, yielding
moderate total precipitation maxima for the next three days.

Elsewhere in the mid-latitudes, a warm front will be retrograding
into the central and northern Patagonia Atlantic coast on Friday
and it will be accompanied by moist air advection, which will
increase precipitation chances and yield moderate total
precipitation maxima. Meanwhile across austral Chile, expect
another frontal boundary to converge into the region on Sunday. It
will be accompanied with a moisture plume. There will be
mid-to-upper level divergence present as well. Expect moderate
total precipitation maxima with this feature.


Tinoco-Morales...(WPC)




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