09/06/2023, 8:02 pm EDT

South America Season 1-3 Ahead Outlook: Southeast Brazil is soaking wet, Central Brazil gains a drought pattern, in the 2023-24 hot season outlook.

Executive Summary: The Climate Impact Company season 1-3 ahead climate outlook is updated. The outlook is valid through meteorological autumn 2024. The forecast is based primarily on the influence of El Nino and also SSTA patterns either side of South America plus the Atlantic tropics. The forecast is consistent with the previous forecast highlighting wet weather risk in Southeast Brazil while Central Brazil drought emerges. Argentina drought continues although late warm season rains emerge to reduce drought intensity in that region. Methodology: The Climate Impact Company season 1-3 ahead climate forecast is valid for SEP/OCT/NOV 2023, DEC/JAN/FEB 2023-24, and MAR/APR/MAY 2024. The constructed analog forecast is based on climate correlation with regional SSTA patterns influential to South America climate. The regions of influence considered for this forecast are ENSO, the marine heat waves east of Argentina and near and east of New Zealand, the Amundsen Sea cool pool southwest of South America, tropical South Atlantic (TSA) index, and the Indian Ocean dipole (IOD). Also heavily considered for the warm season forecast is anomalous soil moisture. Climate discussion: Soil moisture conditions as meteorological spring arrives feature drought centered on Uruguay and into north and east portions of Argentina plus Chile and northwest continent (Fig. 1). Central to southeastern Brazil have observed a wet trend during recent weeks. The 3-month soil moisture trend is somewhat drier (despite recent rains) across much of Brazil to the north-central coast of South America while Chile and western Argentina are somewhat wetter. The global SSTA forecast for DEC/JAN/FEB 2023-24 by ECM indicates peak strength of El Nino 2023-24, an evolving warm phase of the tropical South Atlantic index, a weak (but strengthening) marine heatwave (MHW) east of Argentina and much stronger MHW east of New Zealand and evolving cool pool north and northeast of the Amundsen Sea (Fig. 2). In addition to the robust El Nino is a flourishing positive phase of the IOD. Oceanic El Nino 2023-24 is gaining intensity and currently classified moderate-to-strong although the El Nino climate pattern is lagging. The merge of warm SSTA in the Northeast Pacific with warm SSTA in the Southeast Pacific related to El Nino is required for Ael Nino 2023-24 to become as robust as intense El Nino’s of the past including 1982, 1997, and 2015 episodes. The SSTA merging described is in question. Additionally, the upper ocean heat in the equatorial Pacific has eased slightly during the past month. Thes two diagnostics suggest the El Nino ahead is quite strong but not historically intense. The presence of +IOD with El Nino should cause El Nino climate anomalies to prove stronger. During recent years, high-pressure ridge areas forming across the MHW east of Argentina and ridging across Argentina or into Brazil have caused hot season droughts. This year, the Argentina MHW is not as strong as recent years and is less of a factor. The semi-permanent New Zealand MHW is redeveloping and forecast to shift eastward but not reach the Chile Coast. This warm SSTA feature can also enhance drought risk by causing high pressure in the South Pacific to reach across central South America enhancing drought risk. Finally, the Amundsen Sea cool pool reforms due to ice melting in that region. Upper troughs form in this area and can extend to southern portions of South America during the warm season causing wet climate. TSA index has recently trend toward neutral phase due to the south-to-north passage of cross equatorial wind (positive phase Atlantic meridional mode) pushing anomalous warm SSTA into the tropical North Atlantic where warming is at record level. However, ECM indicates a resurgent +TSA for summertime. The +TSA regime may add rainfall to the Brazilian climate which is typically dry during El Nino. The constructed analog approximates past conditions when El Nino and +IOD were present including MHW’s either side of South America plus warmer than normal tropics. Fig. 1: Daily soil moisture anomalies across South America. Fig. 2: ECM global SSTA forecast for DEC/JAN/FEB 2023-24 and regions of influence on South America climate. SEP/OCT/NOV 2023: The prevailing upper air pattern projected across South America during meteorological spring 2023 features a strong high-pressure ridge anchored over East Brazil while an elongated upper trough stretches west-to-east across Central Argentina. The sensible weather for spring averages somewhat warmer than normal across Brazil with a cool bias in Argentina. Thematically, the forecast does not change much from the previous outlook. The spring season favors wet climate across Southeast Brazil, Paraguay, Northern Uruguay, and far northeastern Argentina. Conversely, a sharply drier transition occurs into East Argentina and central and western Brazil. During spring, drought persists in Argentina, strengthens in central Brazil, while wet soils increase in Southeast Brazil. Fig. 3-4: The Climate Impact Company constructed analog forecast of temperature and precipitation anomalies valid for SEP/OCT/NOV 2023.  DEC/JAN/FEB 2023-24: During summer the upper ridge pattern continues across Brazil. The subsidence creating the persistent ridge is compensation for rising vertical currents over the warm El Nino waters northwest and west of South America. The sensible climate forecast features a hotter than normal summer for most of Brazil. The persistent anomalous heat avoids Argentina. The rainfall pattern features drought reducing rains in Argentina while Paraguay and parts of Southeast Brazil are wet. Coastal Southeast Brazil is drier than normal and drought across Central Brazil intensifies rapidly. Fig. 5-6: The Climate Impact Company constructed analog forecast of temperature and precipitation anomalies valid for DEC/JAN/FEB 2023-24.  MAR/APR/MAY 2024: During autumn, an amplified upper ridge forms over southern continent while continuing across much of Brazil. The forecast maintains anomalous heat across Brazil while Argentina is cooler. Once again there is no significant change from the previous outlook. The rainfall pattern is wet across Southeast Brazil where flooding could continue. A sharp transition to dryness for the remainder of Brazil. Central Brazil drought expands during autumn. Fig. 7-8: The Climate Impact Company constructed analog forecast of temperature and precipitation anomalies valid for MAR/APR/MAY 2024.