By Camilo Diniz
An extratropical cyclone that formed over the Atlantic Ocean, close to Brazil's southern and southeastern coast, will affect the weather across much of the country on Thursday (Nov. 5) and Friday (Nov. 6). A mix of humidity, heat and instability already has millions of people under storm warnings, with a risk of thunderstorms and wind gusts.
The system is organizing a channel of moisture that crosses the Center-West, the Southeast and the north of the South Region. At the same time, it is pushing a cold front across the ocean, which should lower temperatures somewhat, especially in São Paulo. Meanwhile, a high-pressure area keeps the west and south of Rio Grande do Sul stable.
São Paulo at the center of the storm warnings
Brazil's largest city, São Paulo, is inside the orange storm warning area, as is the border with Paraná state. On Thursday, instability begins in the morning along that border and moves in the afternoon to inland São Paulo state, south-central Minas Gerais, Rio de Janeiro and southern Espírito Santo. At night, rain with thunderstorms should reach practically the entire region.
The heat does not leave before the rain arrives. Thursday's forecast highs are 31°C in São Paulo, 34°C in Belo Horizonte and 35°C in Rio de Janeiro. On Friday the contrast shows: São Paulo's high should not pass 21°C, while Belo Horizonte can still reach 34°C.
Paraná and Santa Catarina under alert
In Paraná, instability eases gradually on Thursday. The center-north of the state remains under an orange warning, while the rest of the state and the center and north of Santa Catarina are under a yellow alert. Curitiba and Florianópolis fall within the warning area. A yellow alert for coastal winds covers the northern coast of Rio Grande do Sul and the coast of Santa Catarina.
In Rio Grande do Sul, the weather improves through the day, with clearer skies by night and highs of 25°C in Porto Alegre and Curitiba. On Friday, rain is concentrated in northern Rio Grande do Sul and northern Paraná, where showers with isolated thunderstorms are forecast.
Center-West, North and Northeast
The south of Mato Grosso do Sul, on the border with Paraná, is under an orange warning. The rest of the state, southern Goiás and the Federal District have a yellow alert. Goiânia and Cuiabá may reach 35°C on Thursday, and Goiânia should repeat that mark on Friday.
In the North Region, muggy heat comes with showers in Rondônia, Acre, Amazonas and western Roraima. A yellow warning for heavy rain covers southwestern Roraima, Amazonas, the far north of Rondônia and Acre. Amapá and the coast of Pará stay with steadier weather.
While the South and Southeast face thunderstorms, much of the Northeast remains dry, with strong sun and intense heat on the coast and in the semi-arid interior. Rain is limited to parts of western and southern Maranhão, southwestern Piauí, and western and southern Bahia. Teresina may hit 39°C on both days, the highest heat forecast in the country for the period. Salvador, Natal, Fortaleza and São Luís should reach 32°C.
Why it matters
The alerts span several states in Brazil's most populous and economically important regions, including São Paulo, Rio de Janeiro and Belo Horizonte. Weather can change quickly from one state to another, as the contrast between São Paulo and Belo Horizonte shows. Residents in alert areas are advised to follow the forecast, avoid open areas during thunderstorms and watch for wind gusts.
VDD Analysis
A cyclone that changes the temperature in one day and drops São Paulo to 21°C the next shows how weather can catch the population by surprise. When an alert covers so many states, it is up to the authorities and the Civil Defense (Brazil's civil protection agency) to act ahead of time, and up to citizens to look after their own safety using reliable information.
