320
FXUS20 KWBC 141906
PMDSA

South America Forecast Discussion - International Desks
NWS Weather Prediction Center College Park MD
306 PM EDT Mon Sep 14 2026

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

Forecast Bulletin 14 September 2026 at 1900 UTC:

In Colombia and northern Ecuador high precipitable water (PW)
levels, exceeding three standard deviations above normal for this
time of year, combined with significant low-level potential
vorticity and steady strong northwesterly moisture advection
across western will support widespread heavy rainfall today. As
this dynamical setup moves offshore through Tuesday and Wednesday,
onshore low-level moisture advection will weaken and PW will
decrease slightly. Consequently, areas of heavy accumulation will
become more isolated over the next two days, although locally
significant precipitation remains likely.

Strong low-level moisture advection in addition to diurnal heating
and orographic forcing will trigger areas of heavy rainfall across
the northwestern and western Amazon today. A mid-level ridge
extending from the state of Acre, Brazil, into the Pacific will
limit maximum rainfall accumulations to 15-20 mm over the Central
Peruvian Andes. As the ridge continues moving eastward into
Brazil, a stronger mid-level flow will develop on its western
flank advecting moisture further south into Bolivia and increasing
mid-level potential vorticity to trigger showers over the Bolivian
Altiplano on Wednesday. Maximum rainfall accumulations of 15-25 mm
are likely across portions of the southern Peruvian Andes on
Tuesday and, with similar totals expected over the Bolivian
Altiplano by Wednesday. There is a potential for locally higher
totals on Wednesday over the region of the Bolivian Altiplano.

A strong mid-to-upper level trough will enhance areas of
significant potential vorticity aloft while interacting with a
cold front moving through southeastern Brazil today. Heavy
precipitation is forecast in Rio de Janeiro, with maximum daily
rainfall totals of 30-60 mm today, while the southern Parana Basin
into Serra do Mar can expect a maximum of 20-35mm. The atmospheric
setup will shift east-northeast by Tuesday. A slight decrease in
low-to-mid-level moisture is expected to reduce daily rainfall
accumulation totals to maxima of 15-25 mm, and locally heavier
amounts remain likely along coastal areas from So Paulo to
Esprito Santo and into southern Minas Gerais on Wednesday.

An upper-level trough and its associated cold front will move
across the Patagonia region today, favoring trace snowfall
accumulations over Central Patagonia. A pair of mid-to-upper level
troughs will move into Austral Chile from Tuesday to Wednesday,
increasing moisture advection and interacting with local terrain
to trigger coastal rainfall and mountain snowfall accumulations.
Expect daily rainfall accumulations to remain below 15mm daily in
Austral Chile, while mountain snow totals are expected to reach
15-20cm, primarily on Wednesday.



Sanchez-Perez...(WPC)
Castellanos...(WPC)





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