South Atlantic Cyclone Puts Brazilian Coast on Backwash Alert

The action of a large‑scale extratropical cyclone in the South Atlantic has placed Brazil's coast on alert for marine backwash and waves up to 3 meters. The weather phenomenon directly influences coastal dynamics, stirring up seas that affect the South and Southeast regions in the early days of the week.

Cyclone activity and warnings from the Brazilian Navy

Facing the system's advance, the Brazilian Navy, through the Hydrographic Center (CHM) and the Directorate of Hydrography and Navigation (DHN), issued a bad‑weather warning for backwash risk on Monday (24) and Tuesday (25). The official forecast predicts waves ranging from 2.5 to 3 meters along the shoreline, with an elevated risk also for open‑sea navigation.

Measurements indicate that the southern swell first impacts Rio Grande do Sul and Santa Catarina, where the risk of high tide and backwash persists from Monday (24) through Thursday (27). ECMWF WAM model projections show the agitation intensifying along the Southeast coast, potentially generating waves between 2.8 and 3.7 meters in the most exposed sections of São Paulo and Rio de Janeiro.

Characteristics of the weather system

Identified in GOES‑19 satellite images, the cyclone attracted meteorologists’ attention for its broad area of influence and a pressure of 970 hPa, a typical level for higher latitudes. The system’s circular wind rotates clockwise, pulling polar air masses toward South America.

According to analyses by MetSul Meteorologia, the system is the second of two cyclones expected to affect the region, notable not for rainfall over the continent but for the transport of cold air and the intensity of oceanic winds.

Temperature drop and impacts across South America

Beyond stirring the ocean, the weather system caused sharp temperature drops on the continent. In Brazil, the town of Bom Jardim da Serra recorded a low of –7.7 °C.

Other South American countries also felt significant effects:

• The Argentine National Meteorological Service (SMN) reported thunderstorms, hail and snow in the provinces of Neuquén and Río Negro, with lows of –2 °C and highs of 11 °C.
• Municipalities such as San Carlos de Bariloche and El Bolsón noted the possibility of snowfall.
• Uruguay also lay in the path of the cold air pushed by the cyclone.

New cold front and thunderstorm risk

Although the cyclone begins to drift gradually eastward, away from the continent, stability is not expected to last long. A new cold front is forecast to reach the Southern Region on Thursday (27), according to Meteored.

This new front should raise the risk of heavy rain and severe thunderstorms in Rio Grande do Sul, Santa Catarina and Paraná, later advancing toward São Paulo and Mato Grosso do Sul, with the possibility of intensified severe weather over the weekend.

Information from ND Mais, Diário do Litoral.