South America Forecast Discussion - International Desks NWS Weather Prediction Center College Park MD 156 PM EDT Mon Sep 08 2025 GFS data at ftpprd.ncep.noaa.gov/data/nccf/com/gfs/prod/ South American Forecast Bulletin from 08 September 2025 at 1800 UTC ... In Mid - Latitude South America... In Chile... In the upper levels, the right exit region of a potent jet streak affiliated with a vertically stacked upper trough, that currently has an axis of from 27W to 43W, will begin to promote upper divergence across central Chile starting Monday afternoon. Upper divergence will remain favorable through Tuesday evening as the aforementioned upper troughâ€s axis crosses the Andes. Also starting on Monday afternoon, a mid - level shortwave trough is anticipated to move across south and central Chile. In the low levels, north - northwesterly flow will exceed 50 knots between Coquimbo and Los Lagos through Tuesday morning. During this period, precipitable water values may reach 20mm across Los Lagos, yielding to total precipitation maxima of 20 - 35mm with the risk for cumulonimbus from Monday morning through Tuesday morning. Meanwhile, between Los Rios and Coquimbo, precipitable water values may reach 38mm and may favor a total precipitation maxima of 20 - 45mm from Monday morning through Tuesday morning. Starting Tuesday morning, the mid - level trough will become more negatively tilted, favoring an increase in instability across south - central Chile. In the low - levels, a more west - north westerly flow will dominate between Los Rios and Coquimbo, with the wind speeds continuing to exceed 40 knots through midday Wednesday. Thereafter, expect a decrease in both wind speed and precipitable water. The combination of upper level divergence, enhanced moisture convergence, and instability will favor total precipitation maxima of 25 - 50mm between Los Rios and Coquimbo from Tuesday morning through Wednesday morning. Meanwhile, expect total precipitation maxima of 15 - 25mm in southern Chile. Mountain snow is possible as well with this system. In Central Argentina... A cold front will begin to develop early Tuesday morning across northern Patagonia. By Tuesday afternoon, it will be located across the Rio Negro Province. By Wednesday afternoon, the front will be located across from the Santiago del Estero Province and into the Entre Rios Province of Argentina and extending into central Uruguay. In the upper - levels, a potent jet streak and affiliated upper trough will begin to promote upper divergence across La Pampa - Buenos Aires Province beginning early Wednesday morning through Wednesday afternoon. During this period, a mid - level trough and increase in moisture in the low levels will favor the potential for precipitation across La Pampa - Buenos Aires between Tuesday morning and Thursday morning. A daily total precipitation maxima of 15mm is possible in this region. In Argentina, South Brasil, Paraguay, and Uruguay... An upper trough, that currently has an axis at 63W, will continue to favor divergence in its exit region through Tuesday morning across the region. It is accompanied by a weakening jet streak max that will further sustain divergence across southern Brasil and north Uruguay. In the mid - levels, a shortwave trough will favor destabilization, especially across sectors of Paraguay and far northern Argentina. At the low levels, expect cyclogenesis, and frontogenesis, to occur Monday afternoon across Uruguay and Southern Brasil. The developing cold front will be located across Paraguay and south Brasil by Monday evening. Along and ahead of the cold front, expect enhanced moisture convergence. The combination of the cold mid - levels, which will promote instability, upper level divergence, and an increase of moisture from the tropics will yield to total precipitation maxima of 20 - 45mm across southern Brasil, where a slight risk for severe weather is likely. Across the borders of Argentina, Brasil, and Paraguay, expect a total precipitation maxima of 20 - 35mm with a moderate risk for severe weather. Across Central Paraguay, expect a total precipitation maxima of 15 - 25mm with a moderate risk for severe weather. The aforementioned cold front will continue moving northward into Brasil. By Tuesday evening, the front will be located between Serra do Mar and Espirito Santo and into the Cerrado region of Brasil. By Wednesday evening, the decaying cold front will be located across Mato Grosso, the Cerrado region, and Espirito Santo. Elsewhere in Eastern Brasil... A series of low level moisture plumes will continue to impact parts of Espirito Santo Bahia, and Brasilian Nordeste from Monday morning through Wednesday morning. Total precipitation maxima of up to 15mm are possible in this region. A shear line is expected to develop after Wednesday morning, extending across Bahia and yielding a total precipitation maxima of 15mm. In northern Paraguay... From Wednesday morning through Thursday morning, an upper level shortwave trough will help favor a more diffluent pattern across northern Paraguay. This will positively contribute to the sustenance of upper divergence. In the mid - levels, a shortwave trough may help trigger precipitation in this sector and contribute to the destabilization of the vertical column, which could promote severe weather. A significant increase in low level moisture and cyclonic flow will favor total precipitation maxima of 15mm with a slight risk of severe weather. ... In Tropical South America ... In Ecuador and Peru... An increase in low level easterlies will favor moisture convergence and orographic effects through the forecast cycle. A gradual increase in moisture in the low levels is anticipated from Tuesday morning through Thursday morning. From Tuesday morning through Wednesday morning, a total precipitation maxima of 20 - 40mm is possible, and from Wednesday morning through Thursday morning, a total precipitation maxima of 20 - 35mm is possible. Elsewhere in tropical South America, local effects coupled with diurnal processes will help drive precipitation patterns. Low level troughs will also continue to propagate across the region and will be accompanied by moisture convergence, helping yield to higher total precipitation maxima. Tinoco-Morales...(WPC)