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The extended May Day holiday will see the formation of an extratropical cyclone over the Atlantic Ocean, which will push an intense cold front across Southern and Southeastern Brazil. Five states are on alert for intense rains, storms, and wind gusts: Rio Grande do Sul, Santa Catarina, Paraná, São Paulo, and Rio de Janeiro. Accumulations can reach 90 mm in a single day in Rio Grande do Sul, with risk of hail and very rough seas along the coast.
A large-scale extratropical cyclone forms throughout Friday (May 1st) over the Atlantic and advances over the weekend, organizing a cold front that will affect weather conditions in five Brazilian states. The system puts Rio Grande do Sul, Santa Catarina, Paraná, São Paulo, and Rio de Janeiro on alert for intense rains, storms, lightning, moderate wind gusts, and a chance of hail. Predicted accumulations can exceed 90 mm in parts of the West, Center, and Campanha Gaúcha, volumes that represent a risk of flooding, landslides, and widespread disruptions.
The timing of the system is the worst possible: the cyclone hits Brazil precisely during the May Day long weekend, when millions of people travel, visit beaches, and engage in outdoor activities. In addition to the rain on land, the cyclone will make the sea very rough along the coast of the South and Southeast, with a risk of storm surge that can affect beaches and urban waterfronts. The recommendation is to follow the daily forecast and reschedule outdoor activities between Friday and Sunday.
Friday: the cyclone forms and Rio Grande do Sul goes on alert
According to information released by the Tempo portal, Friday (May 1st) marks the beginning of the cyclone’s formation and its associated cold front, with strong instabilities affecting Rio Grande do Sul since the morning. Rain begins in the early hours in the west of the state and spreads throughout the day to other regions, and by nightfall will have reached the entire Gaúcho territory. Conditions are for moderate to locally heavy rain, with intense storms, lightning, wind gusts, and a chance of hail.
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Accumulations can reach 60 mm during the day, with localized amounts exceeding 90 mm in the West, Center, and Campanha regions. The capital Porto Alegre may record heavy rain and lightning as early as the morning, requiring attention from residents in hillside areas and points historically vulnerable to flooding. Isolated rain showers and storms are not ruled out in areas of Santa Catarina bordering Rio Grande do Sul between the afternoon and night.
Saturday: the cold front advances to Santa Catarina and Paraná
On Saturday (2nd), the cold front shifts and begins to affect Santa Catarina and southern Paraná as well. In the early hours, rain still falls in most areas of Rio Grande do Sul, including Greater Porto Alegre, the mountainous region, and the north-central part of the state. Throughout the day, the rain will decrease and become more concentrated in northern Rio Grande do Sul, and by mid-evening, the weather will become clearer again.
In Santa Catarina, rain begins in the early hours and spreads across all regions throughout the day. Stronger showers and isolated storms are expected in the Greater West, central, and southern Santa Catarina. The southern portion of Paraná, including the capital Curitiba, will experience light to moderate rains, with a risk of localized showers and very isolated storms. Saturday will be the transition day, with the cyclone pushing the instability northeast.
Sunday: São Paulo and Rio de Janeiro in the system’s sights
On Sunday (3rd), rain returns to Rio de Janeiro and São Paulo. Already in the morning, the cold front will cause light to moderate rain and moderate to strong winds in eastern São Paulo, including Greater São Paulo, the Paraíba Valley, and the Ribeira Valley, as well as southern Fluminense. The rain intensifies during the afternoon and affects the Metropolitan Region of Rio de Janeiro, Angra dos Reis, Paraty, and the mountainous region.
The forecast requires extra attention on the coastlines of São Paulo and Rio de Janeiro. As the rain will be persistent and voluminous throughout the day, it can cause flooding in urban areas that accumulate drainage problems. Even with the cold front already further away, areas of instability remain over Paraná and Santa Catarina, leaving many clouds and light to moderate rains at any time, with a risk of isolated storms, especially in the state of Paraná.
The risk of rough seas on the coast of the South and Southeast
The extratropical cyclone does not only affect those on land. The system will strongly agitate the sea on the coast of the South and Southeast, generating abnormally high waves and rough sea conditions that pose a danger to swimmers, small vessels, and coastal structures. Beaches with steep slopes and unprotected urban waterfronts are the most vulnerable.
For those planning to enjoy the long holiday weekend at the beach, the rough seas completely change the scenario. The agitated sea is expected to persist throughout the weekend, and the combination of strong wind with high waves makes swimming in the sea extremely risky. The recommendation from the Navy and civil defense agencies of the affected states is to avoid entering the sea during the cyclone’s influence period and to keep a distance from rocky shores and breaking wave areas.
How to prepare for the long holiday weekend with a cyclone
For those traveling between Friday and Sunday through the South or Southeast, the guidance is to monitor the forecast hour by hour and have an alternative plan for outdoor activities. Roads may have flooded spots, reduced visibility, and a risk of hydroplaning, especially on highways crossing Rio Grande do Sul on Friday and Santa Catarina on Saturday. Drivers should maintain a safe distance and reduce speed.
In urban areas, precautions include clearing gutters and storm drains before the rain arrives, avoiding parking in low-lying areas prone to flooding, and not venturing into flooded streets. Civil Defense can be called at 199 in emergency situations, and the five states on alert should keep teams on standby throughout the long holiday weekend. The cyclone crosses all states from the South to the Southeast, but the damage it can cause depends on everyone’s preparation.
Are you traveling for the May Day long weekend or decided to stay home because of the cyclone? Tell us in the comments what the weather is like in your city and if the forecast changed your plans for the weekend.
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