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The polar air mass advancing through Brazil this weekend will drop temperatures in the South and reach the Southeast between Sunday (3) and Monday (4). In Rio Grande do Sul, the drop could be from 21°C to 11°C in a few hours, creating a sensation of thermal shock. The Serra Gaúcha and Catarinense regions may register lows near 0°C with risk of frost, and the cold will advance eastward to Rio de Janeiro, with highs between 14°C and 24°C throughout Sunday.
A polar air mass is crossing the South of Brazil and will cause what meteorologists call thermal shock in a region that hours earlier registered mild temperatures. The frontal system that brought intense rains and storms to Rio Grande do Sul during the long weekend paves the way for the advance of the cold air that is already starting to drop thermometers late this Saturday (2). In some parts of the state of Rio Grande do Sul, the temperature could drop from 21°C to 11°C in a few hours, a 10-degree drop that surprises those who did not follow the forecast.
The cold will not be restricted to the South. The polar air mass advances coastally and will dominate the eastern part of central-southern Brazil throughout Sunday (3), reaching from the Florianópolis region to Rio de Janeiro. In addition to instability, these areas will experience a drop in temperatures with highs ranging between 14°C and 24°C, significantly lower values than those recorded in previous days. For those who were enjoying the warm long weekend, the change in weather will be abrupt.
The 10-degree drop in a few hours that generates thermal shock
According to information released by Tempo, the phenomenon that meteorologists classify as thermal shock occurs when the temperature drops abruptly within a few hours, not days. In Rio Grande do Sul, where the central part of the state registered temperatures close to 21°C during Saturday, the trend is a drop to 11°C by the end of the night, a 10-degree variation that requires the body to adapt to drastically different conditions in less than six hours.
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For health, the sudden drop represents a risk especially for the elderly, children, and people with respiratory problems. The body, which was regulated for a mild day, needs to adjust quickly to the cold, and this transition can worsen cases of asthma, bronchitis, and cardiovascular diseases. The recommendation is to keep warm clothes nearby even if the day starts warm, because the polar air advances quickly and without warning.
The advance of cold air through the South between Saturday and Sunday
image: meteored
The polar air mass begins to act in Rio Grande do Sul between late afternoon on Saturday (2) and Sunday (3), dropping temperatures throughout virtually the entire state. The cold air advances with greater intensity through eastern Rio Grande do Sul, a region that includes the Serra, the coast, and Greater Porto Alegre, where the concentrated population feels the effects more immediately.
In the first hours of Sunday, the system already reaches Santa Catarina and promises low to mild temperatures throughout the entire state of Rio Grande do Sul and in the Serra Catarinense. The forecast model indicates a risk of frost with temperatures between 5°C and 7°C in areas from the south to the north of Rio Grande do Sul, and considering the correction of 1°C to 2°C for temperatures measured near the grass, the scenario enters the threshold for frost formation in several regions.
Lows near zero in Serra Gaúcha and Catarinense
The Serra Gaúcha and Serra Catarinense will be the areas most affected by the polar air mass. With clear skies during Sunday morning, heat loss is greater, favoring temperatures near 2°C in São Joaquim (SC) and 4°C in Vacaria (RS). With surface measurement adjustments, these values can approach 0°C and even register negative temperatures in isolated spots.
The possibility of frost is real and concerns rural producers in the mountainous region who cultivate vegetables, fruits, and tobacco. The formation of ice on vegetation can destroy entire crops in a single morning, and those who have not adopted preventive measures such as sprinkler irrigation or seedling covers may suffer significant losses. For urban residents, the recommendation is to double protection against the cold and avoid prolonged outdoor exposure during the early morning.
The Southeast in the path of polar air: from Florianópolis to Rio de Janeiro
Throughout Sunday (3), the polar air mass continues to advance and begins to dominate the eastern part of central-southern Brazil. The cold affects from Florianópolis to Rio de Janeiro, with highs ranging between 14°C and 24°C depending on proximity to the coast and altitude. For cities like São Paulo and Rio, which had been experiencing warm days, the change will be noticeable and accompanied by atmospheric instability.
The coastal trajectory of the polar air mass explains why the Southeast is more affected on the coast than inland. The cold air advances across the ocean and penetrates the coast, cooling coastal cities first and only later reaching inland regions with less intensity. For those who planned a beach trip during the long weekend, Sunday brings temperatures that discourage swimming and require a jacket even on the sand.
What to expect in the coming hours and how to prepare
The meteorological sequence is clear: heavy rain in Rio Grande do Sul on Saturday, arrival of polar air late afternoon, thermal shock at night, and a freezing Sunday morning with risk of frost in the mountains. The cold advances to Santa Catarina, Paraná, and the eastern Southeast throughout Sunday, and the influence of the polar air mass is expected to persist until Monday (4) before beginning to weaken.
For those in the South of Brazil, the advice is to follow the hourly forecast, keep warm clothes accessible, and protect cold-sensitive plants before Sunday morning. For those in the Southeast, preparation is simpler but no less important: a jacket that seemed unnecessary on Friday might be the most useful item of the long weekend when the polar air arrives without warning and turns a mild day into an early winter night.
Have you already felt the cold arriving, or has the polar air mass not yet reached your city? Tell us in the comments what the temperature is now where you are and if you were caught by surprise by the sudden drop in thermometers.
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