Extratropical cyclone hits the South Region in the next few days

Between this Friday (22) and next Sunday (24), areas of instability formed by heat and high humidity, in addition to the presence of disturbances in the flow (short wave troughs at mid-levels of the atmosphere) will cause storms in the center -south of Brazil. This pattern precedes the formation of an extratropical cyclone and the passage of a cold front between the end of Sunday and the course of Monday (25) through the southern region of the country.

Starting in the afternoon and evening today, instability will gain strength again and cause storms in Rio Grande do Sul, Santa Catarina and southern Paraná. The forecast indicates a risk of heavy rain, winds above 70 km/h and hail.

On Saturday (23), the storms are concentrated between the north of Rio Grande do Sul, Santa Catarina, Paraná, Mato Grosso do Sul and in areas of the Southeast Region. In these areas, there is also the possibility of heavy rain and wind gusts above 70 km/h.

The formation of an extratropical cyclone between Uruguay and the south of Rio Grande do Sul begins at the end of Sunday and, mainly, in the early hours of Monday. Throughout this day, the system intensifies over the Atlantic Ocean, off the coast of Rio Grande do Sul (figure 1).

Also in the second (25), the convergence of humidity associated with the formation process of this system and the encounters of hot and humid winds from the north and colder winds from the south, give rise to the formation of areas of instability over a large part of the South Region, with forecast of intense rain, gusts of wind and hail.

Winds directly associated with the cyclone and the atmospheric pressure gradient (low pressure in the ocean and entry of high pressure to the west) intensify wind gusts that can reach between 80 and 100 km/h, in the east of Rio Grande do Sul and Santa Catarina, between Monday night and Tuesday morning (26), as shown in figures 2a and 2b.

Throughout Tuesday, the cyclone will gain even more strength, however, it will be on the high seas. On this day, in the eastern part of the entire South Region and also in the states of São Paulo and Rio de Janeiro, the weather is windy.

As the cyclone moves over the ocean, a high pressure system, with cold and dry air, favors a drop in temperatures, while the sun returns to predominate throughout the South Region. Also on this day, temperatures begin to decline in the three southern states, in Mato Grosso do Sul and east of the Southeast Region (figures 3a and 3b).