841
FXUS20 KWBC 032050
PMDSA

South America Forecast Discussion - International Desks
NWS Weather Prediction Center College Park MD
450 PM EDT Wed Jun 03 2026

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

Forecast Bulletin 03 June 2026 at 2045 UTC:


The active pattern across the northern tier of the continent
persists while a series of upper level troughs continue to
traverse the mid-latitudes and subtropics over the next three
days. The most significant rainfall through the period remains
focused across northern South America in association with a train
of tropical waves, while a low level trough near Buenos Aires
supports periods of strong convection across the area. The
remainder of the continent will see a comparatively quiet and
drier regime.

In the tropical South America, a series of tropical waves and
embedded low level
troughs will continue to govern the precipitation regime across
the northern extremes of the continent. For the rest of today and
tonight. As these low level features interact with the mountainous
terrain of Venezuela, enhanced moisture pooling and orographic
ascent will reinforce low level cyclonic rotation, which will keep
the environment highly conducive to thunderstorms. This will yield
enhanced total precipitation maxima with rainfall totals up to 50
mm across portions of Venezuela and northern Brasil. Along the
Pacific coast, onshore low level flow converging into the high
terrain of western Ecuador, aided by a long fetch moisture plume,
will support the highest accumulations in the region, with maxima
reaching 60 to 80 mm.

Through Thursday, the tropical waves crossing northern South
America will continue to produce significant shower and
thunderstorm activity, particularly over Venezuela and western
Ecuador. As the leading wave shifts west toward Colombia, enhanced
upper diffluence over these features will strengthen vertical
ascent, supporting daily elevated total precipitation maxima with
totals up to 80 mm in the most favored areas. The persistence of
onshore flow and orographic forcing will keep the heaviest activity
anchored to the windward terrain. Across the southern cone, a low
level trough situated just north of a stationary frontal boundary
will support the increase in moisture convergence across the
Buenos Aires region. The advection of moist air into the boundary,
combined with weak vorticity maxima rounding the larger scale
trough, will favor strong showers and thunderstorms, with a
marginal risk of severe weather that is favored during the
overnight hours.

In the subtropics and across eastern Brasil, a broad upper level
troughing pattern remains aligned between the subtropical and polar
jet streams. The subtropical upper trough continues its eastward
progression with an embedded jet streak max providing periods of
enhanced divergence across the Bahia region. In the low levels,
easterly and southeasterly flow on the western flank of an offshore
ridge will sustain moisture pooling along the coast, supporting
moderate total precipitation maxima in this region through the
period. Meanwhile, the surface cold front associated with the polar
trough will continue to weaken as it lifts north into the deep
tropics along the Atlantic coast of Brasil, with only light
accumulations expected in its immediate vicinity as the moisture
gradient relaxes.

By Friday, a cold front will approach the southern coast of Chile,
accompanied by increasing mid to upper level forcing and a moisture
plume converging into the region. This will introduce a period of
moderate precipitation along the windward coast and adjacent
terrain. Across northern South America, shower and thunderstorm
activity will persist as the tropical wave train continues to move
across the region, with isolated rainfall totals still surpassing
50 mm in the most active cells. Across the Buenos Aires region, the
remnants of the low level trough will linger behind the departing
boundary, supporting continued shower activity with a marginal
risk of strong thunderstorms. Farther north across the northwest
Amazon, a gradual shift in the low level wind direction toward a
more south-southeasterly component will drive a continued decrease
in moisture and total precipitation maxima with passing days.


Alamo...(WPC)





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