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11/29/2018, 8:21 pm EST

South America Season 1-3 Ahead Forecast

Monitoring required but forecast indicates no harsh drought/flooding for summertime Executive Summary: The Climate Impact Company season 1-3 ahead forecast for South America is updated. CIC is not expecting a major drought during summer 2018-19. Despite periodic heavy rainfall in late spring/early summer flooded fields are not expected to evolve during the summer season. Climate discussion:  SSTA analysis reveals warming off the West Coast of South America (Fig. 1). Meanwhile warming in the eastern equatorial Pacific has warmed to the moderate range. The atmosphere is finally coupling with the El Nino warming off the West Coast of South America. Normally, an El Nino climate causes anomalous warmth across Southeast Brazil, dry conditions in north/northeast Brazil and wet weather in Argentina (Fig. 2). Operational forecasts indicate just-the-opposite condition in Brazil where much above normal rainfall is forecast by all models in the north/northeast portion of the country. Meanwhile Argentina is drier. Why is this non-El Nino climate emerging as El Nino organizes? During late spring a strong positive phase of the Antarctic oscillation (+AAO) which identifies an intense polar vortex across or along coastal Antarctica formed (Fig. 3). The polar vortex has emitted short wave energy propelling cold fronts across South America. Upper support for the frontal systems stalls once off the east coast of South America causing intensifying storms that cool the water surface and maintaining frontal systems extending into Brazil triggering anomalous rainfall. This pattern is expected to ease in December and a full-throttle El Nino climate will develop (Fig. 4). Fig. 1: South Pacific SSTA analysis reveals sudden warming off the West Coast of South America indicating strengthening El Nino.   Fig. 2: El Nino climate anomalies across the globe for DEC/JAN/FEB. Fig. 3: In November 2018 a strong polar vortex emerges over coastal Antarctica emitting short wave energy across South America convening in an upper trough east of Brazil.   Fig. 4: The Bureau of Meteorology/Australia Nino34 SSTA forecast reveals moderate El Nino ahead which dominates South America climate. Outlooks: The outlooks are based on a steady transition to a traditional El Nino climate although El Nino is not particularly strong and accounts for some adjustment in the precipitation anomalies. DEC/JAN/FEB 2018-19: The summer forecast is made with average to below average forecast confidence. Concern is northeast Brazil may not be as dry as forecast. The expected wetter-than-normal zone is across southwest Brazil to Paraguay. The precipitation outlook is about the same as the previous summer forecast. The specific wetter than normal zone stretches from Rondonia to west and south Mato Grosso to Paraguay and touches Formosa and Chaco in northern Argentina. Anomalous heat is expected across much of Brazil and Parana to Minas Gerais could be drier than forecast. Excessive wet soils or harsh drought is not in the forecast. Fig. 5-8: The Climate Impact Company temperature and precipitation anomaly outlook for DEC/JAN/FEB 2018-19. The previous forecast is below. MAR/APR/MAY 2019: Next autumn is warmer than normal across all of Brazil. A dry climate is forecast for northeast Brazil. Wet weather is centered on Bolivia to Paraguay with marginal wet weather in southeast Brazil. Northwest Argentina is drier than normal. Fig. 9-12: The Climate Impact Company temperature and precipitation anomaly outlook for MAR/APR/MAY 2019. The previous forecast is below. JUN/JUL/AUG 2019: The preliminary forecast for next winter is warmer than normal across much of Argentina and Brazil. Dryness dominates north-central portions of Brazil. Near normal rainfall is forecast elsewhere. Fig. 13-14: The preliminary Climate Impact Company temperature and precipitation anomaly outlook for JUN/JUL/AUG 2019.