An extratropical cyclone that begins to form this Thursday (27) over the South Atlantic is expected to keep southern Brazil on alert for at least five straight days, with rainfall totals that could exceed 200 mm in the northern half of Rio Grande do Sul state through Monday (31). The forecast, released by Meteored and detailed in an alert by MetSul Meteorologia, points to a sequence of storms linked to an advancing cold front, with a risk of flooding, landslides and swollen rivers in the states of Rio Grande do Sul and Santa Catarina.
According to ND Mais, Rio Grande do Sul concentrates the highest volumes, with 200 mm forecast for the state. In Santa Catarina, the border strip with Rio Grande do Sul could top 100 mm, while Paraná is expected to total around 60 mm. The timing also raises concern: the south of Rio Grande do Sul may see heavy rain as early as Thursday, Saturday (29) should bring more than 100 mm to the state's southern half, and Sunday (30) tends to be the most critical day in the north, with a potential 150 mm in 24 hours.
MetSul describes the episode as a long-duration event fed by an atmospheric river, a corridor that carries moisture from the Amazon region toward southern South America. In the alert signed by meteorologist Estael Sias, the largest accumulations, from 100 mm to 250 mm through the end of Monday, are expected in areas such as Alto Uruguai, Planalto Médio, the Serra highlands, Aparados and the northern coast of Rio Grande do Sul. That volume should push up the Uruguai, Jacuí, Taquari, Sinos, Caí and Gravataí rivers. Since several of them flow into the northern end of the Patos Lagoon, the Guaíba, in the state capital Porto Alegre, could flood next week, with a high probability of inundation on the city's islands.
Above-average rain spreads across the Center-South
From Monday, the cold front starts advancing over the Center-West and Southeast. The weekly outlook from the ECMWF model, analyzed by Meteored, shows above-average rain across much of Brazil between August 31 and September 7. The largest deviations, 60 mm to 90 mm above the climatological norm, are expected in western Santa Catarina and Paraná; anomalies of 30 mm to 60 mm stretch from northern Rio Grande do Sul to Paraná, and above-normal totals should also reach most of Mato Grosso do Sul, southern Goiás, São Paulo, Rio de Janeiro and southern Minas Gerais. A new frontal system begins to form next Thursday (3) and could keep conditions unstable across the Center-South until at least September 7.
Civil defense mobilized, with 2024 in memory
The Santa Catarina Civil Defense, the state agency responsible for disaster prevention and response, has already issued special warnings. Bulletin 152/2026, signed by meteorologist Augusto Pereira, warns of storms with wind gusts and hail between Friday (28) and Saturday (29) under a semi-stationary front, while another advisory forecasts rough seas along the coast through Friday. The agency publishes updated five-day forecasts and runs a real-time alert system that reaches residents by SMS. In Rio Grande do Sul, the forecast sharpens attention on basins such as the Taquari and the Jacuí, devastated by the historic floods of May 2024, and close monitoring of official bulletins will be essential in the coming days, especially in riverside communities and hillside areas.