The extratropical cyclone that formed on the southeast coast of Rio Grande do Sul on Friday and intensified during this weekend as it moved away from the continent is enormous. Satellite images show that the diameter of its vortex, from South to North, extends for around three thousand kilometers.
An extratropical cyclone is a center of low atmospheric pressure where the wind circulates clockwise in the Southern Hemisphere. Extratropical cyclones are generated by great thermal contrast.
A large area with low pressure favors air elevation, forming clouds with great vertical development with the potential for heavy rain and strong winds with gusts above 100 km/h in their center.
Cyclones are part of the climatology of Rio Grande do Sul, that is, they are common phenomena that can occur at any time of the year. What determines the magnitude of its impacts is the proximity to the continent and how much the pressure will drop in its center.
This weekend’s extratropical cyclone had a minimum central atmospheric pressure below 980 hPa and was responsible yesterday for wind gusts of 90 km/h on both the South and North Coasts of Rio Grande do Sul. In the Southern Plateau of Santa Catarina, the wind on Saturday reached more than 100 km/h.
This huge cyclone over the open sea generated a large swell with storm surge and sea surge on the coasts of southern Brazil and Rio de Janeiro. There was coastal erosion and damage on the coast of Rio Grande do Sul, while in Rio de Janeiro a young man was missing after being swept away by the undertow.
The full-disk hemisphere image from NOAA and NASA’s GOES-16 weather satellite showed the enormous size of this extratropical cyclone in the South Atlantic with its massive cloud spiral in the largest weather system in the entire hemisphere today. The cold front associated with the cyclone reached Espírito Santo and the extreme south of Bahia.
According to an analysis of the European meteorological model at 9am this Sunday, the minimum central atmospheric pressure in the system was 982 hPa. Last night, at 9pm, the pressure was 979 hPa. Yesterday, at 9 am, the pressure was 992 hPa.
The center of the extratropical cyclone was this Sunday morning at geographic coordinates 36ºW and 35ºS, therefore already far from the continent and the Brazilian coast, but the intense wind field over the ocean is very extensive, reaching hundreds of kilometers, and generated the strong swell which brought storm tides and storm surges to the coasts of the South and Southeast of Brazil.
The tendency is for the cyclone to continue moving away from the continent this Monday and for the hangover to decrease in the south of Brazil, but the swell may increase as the swell advances on the coast of the state of Espírito Santo and the southern coast of Bahia.