South America Forecast Discussion - International Desks
NWS Weather Prediction Center College Park MD
1133 AM EDT Fri Oct 16 2026

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

Forecast Bulletin 16 October 2026 at 1535 UTC:

Across the mid-latitudes...
A surface frontal boundary will be arriving into austral Chile on
Saturday morning. There will be a brief increase in precipitable
water values with its passage, where precipitable water value will
reach 20mm briefly. Additionally, there will be vorticity
advection in the mid-levels that will reinforce convergence at the
mid-levels and an increase in upper divergence along the exit
region of an upper level trough. These conditions will favor
moderate total precipitation across austral Chile for Saturday.
Lingering showers and high elevation snow showers are likely to
continue into Sunday across south austral Chile with the passage
of the weakening frontal boundary.

A secondary frontal boundary will be arriving into central Chile
Sunday afternoon/evening. Precipitable water values are also
anticipated to increase with its arrival, surpassing 20mm.
Meanwhile, mid-level vorticity maxima will be moving overhead
during this period, leading to the support of mid-level
convergence and thus ascent. Expect moderate total precipitation
maxima along the higher terrain, primarily being influenced by
orographic effects and light accumulations across the windward
side of the mountains.

Across the subtropics and tropics...
Multiple frontal boundaries will be meandering in the region for
the next three days. Currently, a cold front is located across
south-central Brasil that is expected to transition into a cold
front by Friday afternoon as a result of the development of a
broad cyclonic pattern to its south. Its northward propagation
will become hindered after Saturday as strong northwesterly low
level winds will begin to intensify off the coast of Bahia and
Espirito Santo. The interaction between this front and a low level
ridge to the north will lead to moisture pooling along and off the
coast for the weekend. Thus, the area of greatest precipitation
impact will shift northward in conjunction with the propagation of
the front.

The western extension of the stationary front across the continent
also will begin to lose its definition on Sunday as the general
wind flow pattern begins to shift to a more northerly component
and the thermal gradient weakens in the region. Through the next
three days, expect the daily development of showers and
thunderstorms along this frontal boundary. The environment is
expected to contain deep moisture and instability, suitable for
the initiation of convection.

Another region of interest is along northeast Brasil for Saturday
and Sunday. A broad anticyclonic pattern will be developing in the
region, leading to a north-northeasterly low level wind flow
pattern to converge into the region. Moisture pooling is expected
with this pattern and the development of a local low level trough.
With the increase in moisture and general daytime heating, expect
the enhancement in instability as well. These conditions will
favor daily total precipitation maxima of up to 30mm for Saturday
and Sunday.

Additionally, a broad mid-level anticyclonic pattern will be
developing across the Amazon, leading to the enhancement in
easterly low level winds across the northern half of the Amazon
Basin. This pattern will support the transport of deep moisture
from the east into the region. Thus for Sunday, expect elevated
total precipitation maxima in the vicinity of low level
convergence zones and low level troughs. On Friday and Saturday,
precipitation will be confined to the northwest and west Amazon
Basin where total precipitation maxima of up to 30mm is likely.

In Ecuador, still anticipate the development of diurnal convection
across the north regions of the country. Currently, strong
mid-level winds are helping transport deep moisture across the
northern Andes and into the northwest from the east of the Andes.
These mid-level winds are anticipated to decrease in magnitude
after Saturday. At the same time, the low level wind speed to the
west of the Andes is also anticipated to decrease through the
weekend but the wind direction is expected to gain a more
northerly component. This wind direction change will support the
transport of moisture into northern Peru. Thus, for the next three
days, expect the initiation and sustenance of diurnal convection
across the region, particularly across the Colombian Pacific coast
and Ecuador, where total precipitation maxima will reach 45mm
daily. The period with the greatest precipitation accumulations
will be for Friday and again increasing on Sunday for a broader
region.


Tinoco-Morales...(WPC)