South America Forecast Discussion - International Desks
NWS Weather Prediction Center College Park MD
1236 PM EDT Fri Mar 14 2025

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

SOUTH AMERICAN FORECAST BULLETIN 14 March 2025 AT 13:00 UTC

...Climate/Teleconnections Conditions...
MJO: At this time the MJO continues to be in phase 2. The enhanced
convective phase is currently crossing Africa and entering the
Indian Ocean Basin. This phase also shows enhanced precipitation
over the eastern part of Brasil on Friday and Saturday. As the MJO
continues propagating, the large-scale upper-level convergence
over the Americas will be increasingly limiting the coverage of
deep convection.

ENSO conditions: La Nina advisory persists, while a transition to
ENSO neutral is expected from March to May.

...Synoptic conditions over tropical South America...

Elevated sea surface temperatures (SSTs) in the eastern Pacific,
coupled with the Pacific Intertropical Convergence Zone (ITCZ) and
weak onshore winds at lower levels, will create conditions
conducive to moisture movement inland. This, along with the sea
breeze process and upper-level divergence, will likely promote
isolated diurnal convection along the coast of Ecuador and
southern Colombia by Sunday. Overall,  a slight reduction in
moisture influx and rainfall is anticipated from Friday evening
into Saturday. However, by Sunday, we expect an increase in
moisture influx, leading to peak precipitation rates.

The following maxima are expected over the coast of Ecuador: 
Friday: 20 - 45mm
Saturday: 30 - 60mm
Sunday:  30 - 60mm

The following maxima are expected over the southwest Coast of
Colombia:
Friday: 20 - 45mm
Saturday:  30 - 60mm
Sunday:  30 - 60mm

The transport of moisture by trade winds around the Intertropical
Convergence Zone (ITCZ) is expected to persist, combined with
upper-level divergence, which will enhance precipitation along the
northern segment of the NET/ITCZ. This will particularly impact
northwestern Brasil, as well as southern Venezuela and Colombia,
over the next three days.

The following maxima are expected over Southern Venezuela and 
Colombia:
Friday: 30 - 60mm
Saturday:  20 - 45mm
Sunday:   20 - 35mm

The following maxima are expected over northwestern Brasil:
Friday: 25 - 35mm
Saturday:  20 -35mm
Sunday:  15 - 25mm

...Synoptic conditions for Brasil...
Northeastern Brasil: Upper-level divergence, in conjunction with
the transport of humid air  by  trade winds approaching the
northeast coast of South America from Guiana to northeastern
Brasil, will promote convergence along the coast. For the next
three days, northeastern Brasil will continue to be affected by
moisture influx at low levels due to weak tropical perturbations.
However, these conditions will be less pronounced compared to
earlier in the week. Despite the ongoing moisture transport,
upper-level conditions are not expected to adequately support deep
convection. As a result, while some isolated precipitation may
occur, significant rainfall is unlikely during this period.

The following maxima are expected along the northeast coast of
Brasil:
Friday: 15 -25mm
Saturday: 20 - 35mm
Sunday: 25 - 50mm

The following maxima are expected along the Guinas:
Saturday: 20 - 35mm
Sunday: 30 - 60mm

Southern Brasil: A persistent and expansive high-pressure system
in the low to mid troposphere centered between Pantanal and
southeast Brasil will promote moist easterly to northeasterly
winds in southwest Amazon and Bolivia, that will result in some
showers around the periphery of the high pressure during Friday
And Saturday. In the Serra do Mar, local effects such as sea
breezes, combined with an approaching frontal boundary, will
increase the likelihood of showers and thunderstorms from Friday
(today) through Sunday.

The following maxima are expected in Serra do Mar:
Friday: 15 - 25mm
Saturday: 20 - 45mm
Sunday: 20 - 45mm

...Synoptic conditions for Bolivia, Paraguay, Uruguay and
Argentina and Southern Brasil...

From Friday (today) through Saturday, a zonal upper-level jet will
be positioned over northern Argentina and southeastern Brasil.
This jet stream will contribute to enhanced weather activity in
the region. From Friday (today) through Saturday, a mid-level
short wave will be moving over northern Argentina and Paraguay.
Furthermore,  the frontal boundary at the lower levels will
contribute to the instability of the atmosphere. This system will
bring limited potential for showers and localized thunderstorms
across Paraguay and the Parana Basin in Brasil from today (Friday)
into early Saturday. After that, by Sunday, drier air at mid
levels will be dominating over northern Argentina and central
Paraguay and as the strong surface high pressure system advances
on Friday, dry and stable conditions will prevail over northern
Argentina, Uruguay, and partly southeastern Paraguay.

The following maxima are expected over Paraguay:
Friday: 30 - 60mm
Saturday: 30 - 60mm
Sunday: 15 - 25mm

By Saturday evening , a weak upper-level trough and a short wave
at mid-levels will move across central Argentina, interacting with
a surface low pressure system. This combination will create a line
of convergence over central Argentina primarily affecting southern
Cuyo and northern Patagonia. The sea breeze will enhance moisture
convergence over the northern Patagonia coast, promoting increased
convection and higher precipitation rates. Expect scattered
showers and thunderstorms, particularly in the afternoon and
evening hours, with the potential for localized heavy rainfall
rates and slight risk of severe weather. By Sunday, drier and more
stable conditions are anticipated as another surface high-pressure
system advances into the region. This shift will likely lead to a
reduction in cloud cover and a decrease in precipitation,
resulting in clearer skies and more settled weather across the
area.

The following maxima are expected over Argentina (mostly over Cuyo
and northern Patagonia):
Saturday: 15 - 25mm

In Bolivia and Peru, easterly winds at both the low and upper
levels will enhance moisture influx from the interior of the
continent. Further the Bolivian high will be promoting upward
motion over northern Bolivia and eastern Peru. In the Altiplano
and southern Peru diurnal convection will be enhanced due to an
upper trough and jet dynamic approaching from the southwest,
favoring precipitation maxima on Friday and Saturday.

The following maxima are expected over the northern region of
Bolivia:
Friday: 15 - 25mm
Sunday: 15 - 25mm

The following maxima are expected over Peru:
Friday: 15 - 30mm
Saturday: 20 - 35mm
Sunday: 30 - 60mm

The following maxima are expected over the coast of Peru:
Friday: 15 -25mm
Saturday: 20 - 35mm
Sunday:15mm

...Synoptic conditions for Chile...
In central and southern Chile, the advancing surface high-pressure
system, known as the South Pacific anticyclone, this system will
favor subsidence, which dampens vertical movement and limits cloud
development, therefore stable conditions will prevail over the
next three days. [This anticyclone will favor subsidence and limit
the vertical development of the cloud formation, promoting fair
weather. 

 In the southern and austral regions, conditions will also remain
predominantly stable, with the presence of stratiform
Clouds by Friday and Saturday. By Friday, an upper-level jet is
expected to move into the Zona Austral, aiding in the development
of stratiform rain. However, low-level moisture advection is
anticipated to be limited, which may restrict the intensity of
precipitation. A precipitation maximum of 15mm is expected on
Friday and Saturday. By Sunday a weak moisture plume will be
approaching the region and in combination with the upper level
through it will facilitate the ventilation and the upward motion
to develop rainfall activity.

The precipitation maxima over the Zona Austral is expected to be
around:
Friday: 15mm
Saturday: 15mm
Sunday: 20 - 45mm

For more QPF graphical information:
https://www.wpc.ncep.noaa.gov/international/sam_day1-3.shtml

Ledesma...(WPC)
Alamo...(WPC)