Extratropical cyclone brings damaging winds and coastal flooding to Rio Grande do Sul, Brazil

The Brazilian National Institute of Meteorology (INMET) and the Brazilian Navy Hydrographic Center (CHM) reported that the system developed off the southern coast on July 27 and rapidly deepened while moving east-southeast.

Sustained winds exceeded 90 km/h (56 mph) in many locations, with maximum gusts of 105 km/h (65 mph) recorded in Porto Alegre.

Along the coastline, waves between 2.5–3.5 m (8.2–11.5 feet) were observed, prompting marine hazard warnings from Mostardas (RS) to Florianópolis (SC).

The cyclone formed in association with a strong cold front and was driven by a sharp thermal contrast between polar air over the continent and warmer waters of the South Atlantic.

Surface pressure fell rapidly, consistent with a deep extratropical low. Satellite imagery showed a well-defined cloud shield with strong convection along the frontal boundary.

The Brazilian Navy classified sea conditions as muito grosso (very rough) and issued “ressaca” alerts for coastal communities.

Winds caused significant infrastructure damage across coastal and inland municipalities. In Porto Alegre and surrounding areas, gusts of 105 km/h (65 mph) caused widespread roof damage, uprooted trees, and downed power lines.

Severe coastal erosion and flooding affected low-lying streets in Tramandaí, Imbé, and Torres. Prolonged high winds disrupted ferry operations in Pelotas and damaged rural infrastructure. Inland municipalities including Canguçu, Osório, and Viamão reported damage to crops, rural roads, and electricity distribution networks.

State utility companies reported peak outages affecting approximately 430 000 customers. Restoration work was hampered by debris and unstable weather conditions.

The Rio Grande do Sul Civil Defense confirmed damage in over 20 municipalities, with reports of school closures and transport disruptions.

Reet Kaur

I’m a science journalist and researcher at The Watchers, contributing to the Epicenter edition, where I cover peer-reviewed scientific research and emerging discoveries across Earth and space sciences. With a background in astronomy and a passion for environmental science, I’ve worked in shark and coral conservation in Fiji, conducting reef and shark-behavior research, contributing to mangrove restoration, and earning PADI Open Water and Coral Reef Certifications. I bring a blend of scientific rigor and storytelling to illuminate the discoveries shaping our planet and beyond.

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