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MetSul Meteorology warns that a new cold air mass with an oceanic trajectory will begin to enter Rio Grande do Sul on Saturday (2) and will drop temperatures in the South and part of the Southeast of Brazil in the coming days. Wind gusts can reach 60 km/h on the Gaucho coast. The early mornings of Sunday (3) and Monday (4) will be the coldest, with minimums close to 0°C in the Southeast Serra and Campos de Cima da Serra, and a risk of frost in dozens of municipalities in Rio Grande do Sul.
A new cold air mass is on its way and will affect the South and part of the Southeast of Brazil this holiday weekend and at the beginning of next week. MetSul Meteorology reports that the cold air will be driven by an intense extratropical cyclone far to the South of the Atlantic Ocean and will arrive associated with a high-pressure center advancing from the Pacific to the central-south of Argentina. The wind gusts are expected to reach 50 to 60 km/h on the Gaucho coast and over the Lagoa dos Patos starting Saturday afternoon (2).
This incursion will not be as strong as the one that arrived at the beginning of the week and brought minimums below zero, but it will still have a significant impact. The cold air mass has a maritime trajectory, not continental, which means its effects will be more felt in Rio Grande do Sul, in the east of Santa Catarina and Paraná. For São Paulo and Rio de Janeiro, the cold air arrives on Sunday (3) and drops the temperatures after a sequence of intense heat days that marked the week in both capitals.
What to expect on Saturday with the arrival of the cold air
The cold air should enter with moderate wind from Saturday afternoon to evening (2) in the West, Center, South, and East of Rio Grande do Sul. The gusts should range between 50 and 60 km/h in the most exposed points of the coast and over the Lagoa dos Patos, an intensity that can knock down branches, lift light objects, and cause high waves in small vessels.
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As a consequence of the arrival of the cold air mass, the weather should already improve in part of Rio Grande do Sul on Saturday itself, after the rain that can be strong between Friday (1st) and Saturday due to the action of a cold front over the state. The transition will be quick: the rain stops and the cold enters on the same day, creating a weather change that requires attention from those traveling during the holiday and could be caught off guard by the sudden drop in temperature.
The early mornings of Sunday and Monday with minimums near zero
The coldest early mornings in Rio Grande do Sul and Santa Catarina will be on Sunday (3) and Monday (4). Sunday may start with temperatures around 0°C or even negative in parts of the Southeast Serra, and between 0°C and 3°C in Campos de Cima da Serra, with the possibility of minimums below zero in the São José dos Ausentes region. Much of the Gaucho state should register between 5°C and 10°C.
In Porto Alegre, the minimums should be around 10°C on Sunday and Monday, but in points further South of the city, thermometers may indicate 7°C to 9°C, a mark that repeats in several cities in the metropolitan region. On Monday (4), the cold continues with slightly higher minimums, and on Tuesday (5) the cold air mass already begins to move away with the entry of warmer air that quickly raises the temperatures.
The risk of frost that threatens the South of Brazil again
The cold air mass is expected to cause frost formation again in the South of Brazil, especially on Sunday (3). The probability of frost is higher in Rio Grande do Sul, where dozens of municipalities may wake up with ice on vegetation and surfaces in the areas of the Southeast Serra, Campos de Cima da Serra, and Campanha. The phenomenon is favored by clear skies and calm winds accompanying the high-pressure center.
On Monday, with lows higher, the probability of frost decreases. Frost may still occur in isolated spots and with weak intensity, especially in lowlands of Campos de Cima da Serra, Campanha, and Serra do Sudeste. For rural producers who already suffered losses the previous week, the new wave of cold represents a second blow that requires protective measures even if the intensity is lower than that of the first incursion.
São Paulo and Rio de Janeiro on the cold air route after the heat
Unlike the previous cold air mass, which was restricted to the South, this one should reach areas of the Southeast with noticeable cooling. In São Paulo, the temperature is expected to drop on Sunday (3) with lows around 14°C and 15°C at the end of the day, and highs that may stay below 20°C in several places. The drop is significant for a city that had been recording afternoons above 30°C in previous days.
In Rio de Janeiro, the cold air starts to arrive during Sunday, accompanied by rain which can be heavy. Sunday and Monday afternoons should have much lower temperatures than on previous days in the capital of Rio de Janeiro, ending a sequence of heat that marked the week. As the influence of the cold air mass will be brief in the Southeast, highs will rise again at the beginning of the following week, configuring another typical oscillation of the transition period between autumn and winter.
Why this cold air mass is different from the previous one
The main difference lies in the trajectory. This week’s cold air mass had a continental trajectory, coming from inland Argentina with dry air that dropped temperatures more severely. The new incursion has an oceanic trajectory, advancing through the Atlantic, which makes the cold air more humid and with less capacity to drop the lows to values as extreme as those of the previous week.
The result is significant cold, but not as intense. Lows are expected to be around 0°C in the coldest parts of Rio Grande do Sul, while last week they reached almost -4°C in Bom Jardim da Serra (SC). The maritime trajectory also means that the effects will be more felt in the east of the southern states and less in the inland regions, reversing the pattern of the previous wave.
How to prepare for another cold spell during the long weekend
For those in the South of Brazil, the recommendation is to combine protection against the rain on Friday and Saturday with preparation for the cold on Sunday and Monday. Warm clothes, extra blankets, and attention to the elderly and homeless are priorities on days when lows may drop below 5°C in much of Rio Grande do Sul and Santa Catarina.
For those traveling to São Paulo or Rio de Janeiro during the long weekend, the drop in temperature on Sunday requires a jacket in the suitcase even if the previous days were hot. MetSul will continue updating the forecast with regional details, and the Civil Defense should be called at 199 in emergency situations related to the wind strong or to the frost.
Are you prepared for another cold wave during the long weekend or did you think winter was still far away? Tell us in the comments what the temperature is in your city and if you prefer the cold of the South or the heat that São Paulo and Rio had in recent days.
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