September 7th: Holiday will bring a cold wave to 16 states with temperatures as low as -6°C.

A strong mass of polar air is advancing over Brazil from Friday (4) and should cause an intense cold wave during the September 7 holiday. The phenomenon will mainly affect the South, Southeast and Midwest, with the possibility of widespread frosts and temperatures as low as -6°C.

The cold air initially arrives in Rio Grande do Sul and, on Saturday (5), advances over Santa Catarina, Paraná and Mato Grosso do Sul. On Sunday (6), the polar air mass spreads across much of the Central-West and Southeast.

The upcoming weekend will therefore be marked by a sharp drop in temperatures across much of the country. The intensity of this event is related to the Antarctic Oscillation, an atmospheric pattern that, in its current negative phase, favors the advance of stronger polar air masses towards South America.

The forecast indicates that the cold will gain strength just before Brazil's Independence Day holiday, on September 7th. On Monday (7th), milder than normal temperatures may be recorded in at least 16 states.

Southern Region: Rio Grande do Sul, Santa Catarina and Paraná;

Southeast Region: São Paulo, Rio de Janeiro, Minas Gerais and Espírito Santo;

Central-West Region: Mato Grosso, Mato Grosso do Sul, Goiás and the Federal District;

Northern Region: Rondônia, Acre, southern Amazonas, southern Pará, and Tocantins.

The effects of the cold air mass could still reach the far south of Maranhão and the far south of Bahia, although the probability is lower in these areas. If these regions are considered, up to 18 Brazilian states could be affected by the intense cold spell.

In the South, the main highlight will be the intensity of the cold. Already on Saturday night (5), temperatures could reach negative values in the Serra Catarinense, favoring the occurrence of intense frosts.

The cold will continue to advance during the following hours. In the early morning hours of the September 7th holiday, much of Santa Catarina is expected to register temperatures close to 0°C, with the possibility of widespread frost. Numerical models indicate minimum temperatures as low as -3°C in some areas. With the necessary corrections, however, the forecast points to values that could reach -6°C.

The polar air mass will also cause temperatures to drop below 10°C in the Southeast. The cold weather is expected to reach areas of São Paulo, especially the Paraíba Valley, as well as southern Minas Gerais, near the Serra da Mantiqueira mountain range, and the south and mountainous region of Rio de Janeiro.

Southern Mato Grosso do Sul will also be hit by an intense cold wave. With the advance of the polar air mass, next week should bring below-normal temperatures to much of Brazil.

This episode represents a temporary break in the intense heat pattern associated with El Niño. Despite this, forecasts indicate that very intense heat waves are likely to return frequently during the spring and, especially, the summer.

For the September 7th holiday, the situation requires attention, especially in the southern areas most prone to sub-zero temperatures and frost. The intensity of the cold and the possibility of minimum temperatures near or below zero should be the main points of concern during the advance of the polar air mass.