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FXUS20 KWBC 031835
PMDSA

South America Forecast Discussion - International Desks
NWS Weather Prediction Center College Park MD
134 PM EST Mon Nov 03 2025

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

South American Forecast Bulletin for 03 November 2025 at 1830 UTC

Across South America, the current and forecast synoptic pattern
will favor significant rainfall over portions of the Buenos Aires
Province, as well as Central Paraguay and the Amazon basin. Some
rainfall is expected elsewhere, but the aforementioned sections
could observe over 25mm of rain over the next 3 days, with
isolated higher amounts. Some of the global models suggest that
isolated portions of the Buenos Aires Province, could observe up
to 100mm with strong thunderstorms, most of the rainfall occurring
late tonight into Tuesday.

In the upper levels there is a low pressure across the Pacific,
just west of southern Chile, which has a jet to its north,
entering central to north Chile. There is another broad low
pressure in the southwestern Atlantic, which is producing a strong
jet moving in from the south into the southern cone of South
America, as well as one just east of Buenos Aires. This pattern
causes a diffluent upper-level flow across portions of
northeastern Argentina. Some troughiness can also be observed over
southeastern Brasil, while a high pressure over western Brasil
dominates much of the Tropical South America. By Thursday, the
Bolivia High is expected to develop, creating a strong pressure
gradient further south, and strengthening the upper-level winds
across central Chile into central Argentina into Uruguay and
southern Brasil. In addition, there is a trough about to move into
Chile, and another one east of South America in the Atlantic.

The mid levels are vertically stacked to the upper levels, with
the troughs and low pressures present in the upper levels being
reflected in the mid levels. In terms of wind speeds, the
southerly jet moving into the southern cone is the most
significant int he mid levels, with speeds of up to 90 knots
today, while other areas would have mid level winds of 50 knots or
lighter. By Thursday, the high pressure over Bolivia is present
but displaced a bit to the southeast, as well as not as well
defined as it is in the upper levels. That said, it still will
cause a relatively tight pressure gradient over the central
sectors of the continent, and mid level troughs just west of Chile
and east of Argentina, just like it is the case in the upper
levels.

In the lower levels, a series of low-level jets and troughs will
contribute to low-level moisture convergence over central South
America, which will combine with the mid and upper level dynamics
to produce showers and thunderstorms. The tropical region of South
America will also have some low-level troughs and moisture
convergence, and although the mid and upper levels are not
particularly favorable for deep vertical development, the
combination of the higher than normal moisture will combine with
the diurnal heating and local effects, to produce daily showers
and thunderstorms over the area. The Amazon basin and other
portions of southern Brasil into eastern Brasil possibly observing
the highest amounts of moisture and daily showers and
thunderstorms.


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

Alamo...(WPC)



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