South America Forecast Discussion - International Desks
NWS Weather Prediction Center College Park MD
117 PM EST Fri Nov 07 2025

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

South American Forecast Bulletin for 07 November 2025 at 1820 UTC

A dynamic upper level pattern across subtropical and central South
America will continue for the forecast cycle. A subtropical upper
level ridge will continue to dominate across Brasil through the
weekend. Around the periphery of the upper ridge, upper divergence
may be present especially in regions where there will be
interactions with upper level troughs. On Friday, a shortwave
upper level trough will be moving across Paraguay, northern
Argentina, Uruguay and southern Brasil and its axis will begin to
move into the Atlantic Ocean Basin by Saturday. The interaction
between this trough and the aforementioned upper ridge will favor
a diffluent upper level wind pattern that will further promote
divergence. The upper trough will reflect into the mid-levels and
will be accompanied by a progressive surface frontal system. On
Friday evening, the associated cold front will extend from
southeastern Brasil while an occluded front will be located across
Rio Grande do Sul. The highest precipitation totals from Friday
morning through Saturday morning will be located in the vicinity
of the occluded front. The cooler mid-levels will aid in
increasing instability in this region as well. Expect a total
precipitation maxima of 50 - 100mm across Rio Grande do Sul and
severe weather will be favorable. As this system continues
propagating off coast into the Atlantic, intense moisture
convergence will dominate across the region and may promote a
total precipitation maxima of 30 - 60mm across Brasilâ€s Parana
Basin, central and southeastern Paraguay, and the northern
Mesopotamia region for the same time period from Friday morning
through Saturday morning.

By Saturday, the frontal system will be located across
east-central Brasil. There will be an increase in moisture
convergence across central Brasil on Saturday, which could yield a
total precipitation maxima of 20 - 45mm. Across the Atlantic
coasts Serra do Mar and Espirito Santo, expect a substantial
increase in moisture starting Saturday afternoon. There will also
be upper level support during this period. A total precipitation
maxima of 25 - 50mm is likely from Saturday morning through Sunday
morning. By Sunday, precipitable water will still remain high and
the low level wind flow will be from the east, favoring moisture
convergence and orographic enhancement. However, upper divergence
will be limited. The spatial extent of higher accumulations will
be more isolated, particularly across the Cerrado region of Brasil
and Espirito Santo. Total precipitation maxima of 25 - 50mm will
be possible in these regions.

Another region of interest associated with the aforementioned
frontal system is another cold front that will be located across
Bolivia on Friday and is expected to transition into a stationary
front thereafter. This region will be situated along the periphery
of the aforementioned upper level ridge that will favor an
increase in upper level divergence throughout the forecast cycle.
The day of greatest precipitation impact will be on Saturday when
the weak frontal system is expected to arrive. It will be located
across north-central region of Bolivia on Saturday evening. The
combination of upper level divergence, the presence of a mid-level
trough, and ample moisture will yield a total precipitation maxima
of 20 - 45mm from Saturday morning through Sunday morning.

In the mid-latitudes, a positively tilted upper level shortwave
trough that is off the coast of central Chile will slowly begin
traversing the Andes Mountains during the weekend. This trough
will also be reflected in the mid-levels. At the surface,
troughing will be present across the Cuyo region and long fetch
northerly low level flow will be extending into northwest
Argentina. This flow pattern will help funnel moist tropical air
into the region. These conditions will favor an increase in
precipitation chances throughout the entirety of the forecast
cycle. The period with the most significant precipitation
accumulations will be from Saturday morning through Sunday morning
when a total precipitation maxima of 20 - 35mm is likely.

In the high mid-latitudes, the period with the greatest
precipitation impact will be on Saturday. An upper level trough
will be moving across the area and will be accompanied by a jet
streak max. Upper divergence will be present due to these
features. At the low levels, there will be strong northeasterly
winds moving into austral Chile, with windspeeds exceeding 40
knots. There will be an increase in precipitable water overnight
Saturday into early Sunday morning. Thus, expect moisture
convergence across this region. A total precipitation maxima of 25
- 50mm is possible. Otherwise, seasonal conditions will persist
for Friday and Sunday.

In tropical South America, seasonal conditions will continue for
most of the region. Enhanced easterly and northerly winds will
prevail across the basin and will favor moisture convergence.
Also, the presence of low level troughs will favor the initiation
of precipitation across the region. Local effects and the diurnal
cycle will further enhance precipitation accumulations. A feature
of interest is a low level trough that will be moving across
Venezuela and Colombia starting today through Sunday. On Friday
and Saturday, the greatest impacts associated with this low level
trough will be confined to central and western Venezuela, where
total precipitation maxima will exceed 35mm. By Sunday, this
trough will be located across Colombia and orographic effects may
enhance total precipitation maxima. Another region of interest is
the Panamanian low level trough. A cyclonic low level wind flow
pattern will begin to develop along the Pacific coasts of Colombia
and Ecuador on Sunday. The increase in onshore moist flow will
favor increasing total precipitation maxima.


For the latest available charts please visit:
https://www.wpc.ncep.noaa.gov/international/sam_day1-3.shtml

Tinoco-Morales...(WPC)