South America Forecast Discussion - International Desks
NWS Weather Prediction Center College Park MD
254 PM EST Mon Feb 24 2025

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

South America Forecast Bulletin 24 Feb 2025 at 2000UTC:

In the large scale...
The Madden Julian Oscillation (MJO) has been classified as being
in its Phase 8, indicating an increase in upper level divergence
across the Western Hemisphere. However, the MJO is being observed
as being unorganized. In the next week, models are indicating a
shift to a more convergent phase.

In the upper levels...
The Bolivian High, located near 21S 80W Monday afternoon, will
continue to weaken through Tuesday afternoon. In southeast Brasil,
an upper trough, with an axis across 21S 44W and 35S 27W, will
remain stationary over the area through the next three days, and
may occlude by the end of this week. The interaction between these
two upper level features will yield to an increase of diffluence
across northeast Argentina, Paraguay, Uruguay, and south Brasil
through Tuesday afternoon.

In mid - latitude South America...
In Austral Chile, the period of greatest precipitation impact will
be Monday through Tuesday morning. During this period, an upper
jet streak will be traversing across the region, sustaining upper
divergence through Monday evening. In the mid-levels, a trough
accompanied by vorticity advection will also favor ascent for
convection. In the lower levels, expect ample moisture through
Tuesday morning. However, low level wind speeds will decrease
starting by Monday evening, yielding to a reduction in moisture
convergence and orographic effects thereafter. These conditions
will favor a total precipitation maxima of 20 - 35mm through
Tuesday morning.

In Argentina, for the next two days, a low level meandering trough
will remain across north - central Argentina and Uruguay. Along
and ahead of the trough, moisture convergence will be favorable.
In the mid - levels, a series of shortwave troughs will also help
sustain convection within this region. The period of greatest
precipitation impact will be Monday through Wednesday morning. The
upper level set up for this period are as follows. From Monday
morning through Tuesday morning, upper level diffluence and speed
divergence will be present across north - central Argentina. By
Tuesday morning through Wednesday morning, upper diffluence will
decrease, but speed divergence will remain favorable. Expect total
precipitation maxima of 25  - 50mm for Monday to Tuesday and 30 -
60mm for Tuesday to Wednesday.

In tropical South America ...

In the upper levels, with the weakening of the Bolivian High,
upper level divergence will decrease across west South America. In
its wake, an upper trough is anticipated to develop after Tuesday
afternoon at 13S 78W, though it is expected to quickly weaken as
it interacts with a sub-tropical trough by Friday. Elsewhere in
the region, upper easterlies in northwest South America will begin
to weaken starting Tuesday morning, when westerlies will begin to
dominate the west coast regions of Ecuador and Colombia. It is
important to note that directional wind shear will also increase
after Tuesday morning in this region, acting as a limiting factor
for convective upward development. However, ample moisture
convergence will remain through Wednesday.

In the low - levels, across the west coast of Ecuador and
Colombia, beginning on Monday afternoon, two low level troughs are
developing to the north and south of the equator respectively,
between 90W and 100W starting Monday afternoon. Expect an increase
in low level westerlies to converge across the Ecuadorian coast
through Tuesday afternoon. By Wednesday, the two troughs will
continue to move west into the central Pacific, with low level
wind direction shifting to a more northerly component along the
Pacific coasts of Colombia and Ecuador thereafter. Expect a total
precipitation maxima of 25 - 50mm for Monday through Tuesday
morning, a maxima of 30 - 60mm from Tuesday morning through
Wednesday morning, and 25 - 50mm maxima for Wednesday morning
through Thursday morning.

The ITCZ, NET, and Southern ITCZ will continue to be the main
driving force for convection across the region. Regions of
interest continue to be the northwest section of tropical South
America and northeast South America. Similarly, a series of low
level troughs will continue to traverse the region through the
next three days, increasing the potential for precipitation.


Morales...(WPC)
Ledesma...(WPC)