03/07/2023, 4:45 pm EST

South America Season 1-3 Ahead Climate Forecast

Highlight: Argentina to far Southeast Brazil drought likely to continue but ends with El Nino rains by springtime. Executive Summary: The Climate Impact Company season 1-3 ahead climate outlook is re-issued. The outlook is driven primarily by an ENSO shift from La Nina to El Nino. Forecast highlights include continuation of the Argentina drought with unusually warm temperatures for autumn. However, El Nino rains will drench the Northeast Argentina/Southeast Brazil drought area by next spring. A new drought area for the 2023-24 warm season is not expected at this time. Summer 2022-23 review: During meteorological summer 2022-23, an immense marine heat wave (MHW) was present (again) east of Argentina. Warm SSTA also developed east of Chile as part of an eastward extension of the New Zealand MHW. Across each warm zone of ocean water, impressive upper-level high-pressure ridging developed. Much of summertime observed the branching of subtropical high pressure across Argentina to cause excessive heat, dryness, and drought (Fig. 1-2). To compensate for the high amplitude subtropical/mid-latitude high-pressure ridge, a persistent upper trough emerged over East Paraguay causing heavy rain along the Paraguay/Brazil border to the Brazil Coast due east of Paraguay. To the north of this wet zone, Northeast Brazil became quite dry while the far northern continent was excessive wet. Certainly, contributing to the summer climate was the persistent La Nina climate most evident with the northern continental rains.   The Climate Impact Company summer 2022-23 temperature outlook for South America projected a hot pattern for Northern Argentina and Paraguay with normally hot weather in Brazil except hotter than normal in the Northeast (Fig. 3). Typical of climate forecast verification review nowadays, good forecasts are thematically correct but less successful at capturing the extremes are less successful. The precipitation outlook placed a dry and drought-producing climate pattern directly on East Paraguay and vicinity which was slightly too far to the north (Fig. 4). The outlook did not predict the heavy rains in Southwest Brazil/Paraguay and was too dry in Southeast Brazil. Fig. 1-2: The DEC/JAN/FEB 2022-23 temperature/precipitation anomaly preliminary verification. Fig. 3-4: The DEC/JAN/FEB 2022-23 temperature/precipitation anomaly forecast issued by Climate Impact Company on Oct. 27, 2022. Climate discussion: Changes in the prevailing climate pattern is expected in 2023. First, and foremost, ENSO phase is forecast to shift to El Nino by most forecast models during JUN/JUL. The projection is made during the ENSO springtime prediction barrier (SPB) when ENSO forecast skill historically deteriorates. Consequently, forecast confidence in the rapidly oncoming El Nino for mid-year is below average. Current ocean climate diagnostics indicate neutral Nino SSTA, a dramatic warming of the eastern equatorial Pacific subsurface, and a likely shift into negative phase southern oscillation index (-SOI) all implying an El Nino trend. Newly essential to South America climate, especially during the warm season, is the influence of MHW’s either side of South America in the middle and subtropical latitudes. The Argentina MHW has been the most dominant and is well-correlated to anomalous high-pressure ridging as observed during just-finished summertime. The MHW off the West Coast of South America was an exception and possible early sign that ENSO would begin a phase change away from La Nina and toward El Nino as the up-welling cold Humboldt Current weakened. In the tropics, relevant to trade wind intensity and precipitation influence on South America climate is the SSTA pattern between the equator and 20S latitude. In this zone, the tropical South Atlantic (TSA) index is calculated. During summer 2022-23 the TSA index was slightly positive, more so during February. Forecast methodology for the season 1-3 ahead outlook: The forecast methodology to generate a constructed analog climate forecast for South America for the next 3 seasons is based on ENSO phase, MHW activity, and the TSA pattern. The NCEP CFS V2 model is used as initialization is reasonable when matched against the actual global SSTA pattern (Fig. 5). The MAR/APR/MAY 2023 forecast reveals weak El Nino warming in the equatorial East Pacific while MHW’s either side of South America are slightly weaker. The TSA pattern is toward the warm phase. During JUN/JUL/AUG 2023, El Nino arrives while MHW are weaker and move away from the coasts. The +TSA pattern is intact but weak. Finally, the SEP/OCT/NOV 2023 features a strengthening El Nino, weaker MHW’s, and emergence of the positive phase of the Indian Ocean dipole (+IOD). Fig. 5: The CFS V2 global SSTA forecast for MAR/APR/MAY, JUN/JUL/AUG, and SEP/OCT/NOV and relevant areas to project South America climate. MAR/APR/MAY 2023: The Argentina drought intensified during late summer and continues to act as a magnet to anomalous warmth likely to last well into autumn as the drought also continues. Dryness becomes most intense in Southeast Brazil. Wet weather stretches across Central to Northeast Brazil. Fig. 6-7: The Climate Impact Company constructed analog forecast of temperature and precipitation anomalies valid for MAR/APR/MAY 2023.  JUN/JUL/AUG 2023: The winter outlook has a stronger El Nino signature most obvious with the wet streak across Paraguay to Southeast Brazil and including Northeast Argentina. The Argentina forecast trend is milder while Chile to Peru shifts cooler. Fig. 8-9: The Climate Impact Company constructed analog forecast of temperature and precipitation anomalies valid for JUN/JUL/AUG 2023.  SEP/OCT/NOV 2023: An El Nino is firmly in-place as (very) wet weather is projected next spring for Southern Brazil to Northeast Argentina. Any lingering drought in the southern portion of the wet zone should fade. Much of Brazil is warmer than normal with Argentina averaging near normal. Fig. 10-11: The Climate Impact Company preliminary constructed analog forecast of temperature and precipitation anomalies valid for SEP/OCT/NOV 2023.