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)