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01/30/2024, 12:07 pm EST

The Inaugural South America Year-2 Ahead Climate Forecast

Highlight: Brazil drought shifting south toward Argentina. Executive Summary: The inaugural year-2 ahead climate forecast for South America is issued. The forecast is valid for meteorological autumn 2025 through summer 2025-26. Forecast highlights include a strengthening Brazil drought shifting southward into Northeast Argentina. Climate summary: As discussed in the South America season 1-4 ahead climate summary, the projected ENSO phase for 2025 is La Nina with varying intensity. La Nina is likely to continue through the southern hemisphere summer 2025-26 season. Oceanic warming either side of South America increases in 2025 and the influence on climate by these warm SSTA conditions is averaged with historical La Nina conditions to generate the year-2 outlook. Forecast methodology: The forecast is based on a constructed analog that equally weighs the influence of the 2014-23 oceanic warming across the South Pacific and South Atlantic with modern-day La Nina climate. MAR/APR/MAY 2025: Meteorological autumn 2025 upper air pattern features a semi-permanent upper trough well east of Southeast Brazil while an amplified upper ridge stretches across Central Argentina with two centers either side of the continent. The prevailing climate given this set-up is a variable thermal pattern across both Brazil and Argentina averaging near normal for the season. Central and Southeast Brazil are drier than normal as Brazil drought continues given this rainfall outlook. Northern continent is wet while Argentina observes mixed conditions with wet climate northwest and a dry regime northeast extending across Uruguay. Fig. 1-2: The Climate Impact Company constructed analog forecast for temperature and precipitation anomalies during MAR/APR/MAY 2025 across South America. JUN/JUL/AUG 2025: The prevailing upper air pattern for meteorological winter 2025 is concerning. More so than the winter 2024 forecast, an amplified upper trough is located off the South Coast of Chile and stretches southwestward toward the Amundsen Sea off the Antarctic Coast. Another equally amplified trough is east of Uruguay. If the trough patterns merge during the winter season, an exceptionally chilly air mass could evolve across Argentina and extend northward into Brazil (at times). Consequently, risk of dangerous cold into South Brazil for winter 2025, is above normal for the second consecutive winter. North of this risk, Brazil averages warmer than normal for the winter season. Argentina and especially Chile average cooler than normal.   Fig. 3-4: The Climate Impact Company constructed analog forecast for temperature and precipitation anomalies during JUN/JUL/AUG 2025 across South America. SEP/OCT/NOV 2025: During spring 2025, a dry climate emerges across southwest and southeast portions of Brazil. North/Northeast Brazil is wet. The Brazil drought is shifting southward. Northeast Argentina also shifts drier. Anomalous heat is forecast for Central/Northwest Brazil while a cooler than normal bias exists over Southeast Brazil to North Argentina. Fig. 5-6: The Climate Impact Company constructed analog forecast for temperature and precipitation anomalies during SEP/OCT/NOV 2025 across South America. DEC/JAN/FEB 2025-26: During meteorological summer 2025-26 a major drought is implied in Northeast Argentina and Southeast Brazil by a dry and hot climate forecast in these areas. Prior to summer, southern portions of Brazil are already in drought. Consequently, accelerating drought due to a hostile climate pattern is easily attained. Much of Argentina is hotter than normal for the season. East Brazil is typically rainy with suppressed anomalous heat risk.   Fig. 7-8: The Climate Impact Company constructed analog forecast for temperature and precipitation anomalies during DEC/JAN/FEB 2025-26 across South America.    
01/27/2024, 9:47 am EST

South America Season 1-4 Ahead Outlook: Brazil drought likely to hang on through 2024. Argentina dryness may develop in some (not all) zones.

Executive Summary: The Climate Impact Company season 1-4 ahead climate forecast for South America is updated. The forecast is based on a constructed analog correlating historical upper air patterns with prevailing ENSO conditions and SSTA regimes either side of the continent. Departing summer 2023-24, despite some late summer rains, Brazil soil moisture is mostly below normal, and drought is present for some areas. The 2020-23 Argentina drought eased due to El Nino rains. Looking ahead through 2024 toward the next warm season, climate forecasts favor regenerating drought in Central to East/Southeast Brazil and possibly parts of Argentina to the west and southwest of Uruguay for next spring and summer. The winter season ahead faces above normal risk of a cold surge into Southwest/Southeast Brazil during mid-winter. Climate discussion: Beginning in early 2023, soil moisture conditions featured an intense lengthy La Nina-inspired drought across far Southeast Brazil, Uruguay, and Northern Argentina. Soil moisture conditions have reversed one year later featuring a wet soil profile in Southeast Brazil with general dry soil conditions across the remainder of Brazil. Meanwhile, the long-term drought in Argentina has eroded. The soil moisture reversal is linked to evolution of the 2023-24 El Nino episode. The 2023-24 El Nino episode is unique in that oceanic El Nino (Nino34 SSTA) has been substantially stronger than the attendant reaction of the atmosphere (multivariate ENSO index). Interestingly, the opposite was true of the 2020-22 La Nina (Fig. 1). The explanation is related to the SST gradient between the equatorial region where ENSO phase is measured and the poleward subtropical ocean SSTA pattern. During El Nino, the lack of thermal gradient between the anomalous warm equatorial region and warm SSTA in the subtropics lead to diminished SST gradient correlated to a weaker El Nino climate. During La Nina, the cool equatorial waters vs. the warm subtropics created a large SST gradient correlated to a strong La Nina climate. In this regime, South America La Nina climate should be stronger than El Nino climate. Looking forward, El Nino 2023-24 is expected to weaken over the next few months. Recently, upper ocean heat in the equatorial Pacific diminished rapidly implying the robust El Nino signature at the surface will begin to fade soon. The speed of subsurface cooling increases the validity of the NCEP CFS V2 rapid transition from El Nino in early 2024 to a robust La Nina later this year (Fig. 2). If the NCEP CFS V2 prediction is correct, the Climate Impact Company constructed analog projects La Nina continuing to DEC/JAN/FEB 2025-26 (Fig. 3). In the northern hemisphere, an optimum climate normal (OCN) is used by Climate Impact Company accounting for the tendency of strong warming of the mid-latitude oceans and their influence on the prevailing climate pattern. In the southern hemisphere, this approach is used for the past 5 years (2019-23) due to the persistent robust warming of the ocean surface east of Argentina and the consistently strong marine heatwave (MHW) surrounding New Zealand extending westward toward Chile in recent years. The prevailing influence on the upper air pattern of the oceanic warming described is increased high pressure from west of South America to Brazil. Interestingly, the NMME global SSTA forecast indicates the warm SSTA pattern of the past 5 years is in retreat by the midpoint of 2024. The projections are a closer match to the 2014-18 less aggressive mid-latitude warming. Fig. 1: Oceanic (Nino34 SSTA) and atmospheric (multivariate ENSO index) ENSO conditions are compared for this decade so far. Fig. 2: The NCEP CFS V2 Nino34 SSTA forecast through October 2024. Fig. 3: The Climate Impact Company constructed analog Nino34 SSTA forecast through DEC/JAN/FEB 2025-26. Climate summary: El Nino is confidently forecast to shift into La Nina around or just after midyear. A lengthy La Nina is likely to follow lasting through next year. Unlike the past 5 years when prohibitive warming of the ocean surface on each side of South America occurred, a less robust warm pattern similar to the 2014-18 climatology is forecast through next year. Forecast methodology: A constructed analog based on past similar ENSO regimes combined with the 2014-18 OCN correlated to the atmospheric upper air pattern generates the seasonal forecasts beginning with meteorological spring 2024 and ending with meteorological winter 2025-26. Also considered are soil moisture conditions for the warm season outlooks. MAR/APR/MAY 2024: El Nino shifts to neutral phase. The El Nino climate may linger. Ocean temperatures are much warmer than normal in the South Atlantic tropics. However, waters on either side of the subtropical/mid-latitude coastlines cool to near normal. The projected prevailing upper air pattern for the period features an upper ridge over Brazil fueling a warmer and drier than normal autumn season. To compensate, an upper trough is semi-permanent across Southeast Brazil. The upper trough causes a wet autumn in Northeast Argentina to Southeast Brazil and a cooler than normal climate across Northern Argentina. In Brazil, dry soils regenerate during autumn and any lingering summer drought worsens. Fig. 4-5: The Climate Impact Company constructed analog forecast of temperature and precipitation anomalies valid for MAR/APR/MAY 2024. Previous forecast below. JUN/JUL/AUG 2024: Meteorological winter 2024 produces a semi-permanent upper-level ridge over Brazil while a large upper trough extends from near the Amundsen Sea off Antarctic to southwest of South America. If the Amundsen Sea trough extends to the southern half of South America during mid-to-late winter, risk of a cold outbreak reaching Southern Brazil occurs. Given the weakness in the upper air projection from southwest of South America to east of Uruguay, the risk of the cold scenario is above average. The prevailing winter climate features warmer than normal conditions across the northern half of Brazil and near normal temperature for Southern Brazil to Northern Argentina. Wetter than normal climate is projected for central continent while northern continent is dry. Fig. 6-7: The Climate Impact Company constructed analog forecast of temperature and precipitation anomalies valid for JUN/JUL/AUG 2024.  SEP/OCT/NOV 2024: Meteorological spring 2024 features a stronger than normal subtropical ridge into East Brazil while a strong upper trough off the Southeast Brazil Coast occasionally extends across central continent to drive a wet climate pattern for Southwest Brazil and Paraguay. The upper ridge leaves Northern Brazil warmer than normal while East Brazil is mostly dry. Argentina is unusually cool during the spring season. Drought conditions are likely in Central to East Brazil with a marginal drought risk in Argentina to the west-southwest of Uruguay. Fig. 8-9: The Climate Impact Company constructed analog forecast of temperature and precipitation anomalies valid for SEP/OCT/NOV 2024. DEC/JAN/FEB 2024-25: Next summer season, an upper low is forecast to drop anchor much of the time over Uruguay. Consequently, wet weather is persistent across Southwest Brazil, Paraguay, and Northern Argentina. Just north, East Brazil is dry and hot. Drought conditions are likely to develop east of Paraguay toward the Brazil Coast and northwestward toward Central Brazil. An upper-level high pressure ridge heats Central Argentina where climate is likely drier than normal. The north coast of South America is wet in response to a La Nina climate pattern. Fig. 10-11: The Climate Impact Company constructed analog forecast of temperature and precipitation anomalies valid for DEC/JAN/FEB 2024-25. The year-2 ahead forecast is issued separately.