A formation and action of an extratropical cyclone along the coasts of Uruguay and Rio Grande do Sul will bring intense rain in the South of Brazil, a wave of storms in the Center-South of the country and very strong to intense wind to Uruguay, Rio Grande do South and part of Santa Catarina at the end of this weekwarns MetSul.
O The cyclone that will form will be one of the most intense this year near the south of Brazil with very low atmospheric pressure and accelerated intensification of the system along the Gaucho and Uruguayan coasts, aggravating the potential for strong to intense winds with damage and disruption, especially to the electrical grid.
Extratropical cyclones form when hot and cold air masses meet. This is precisely what will determine the cyclogenesis near Rio Grande do Sul. As is more normal in winter than in November, a mass of cold air that at the beginning of the week brought intense and atypical snow in Patagonia will advance through Northern Argentina and the Meeting with hot air over Brazil will deepen low pressure from Uruguay and Rio Grande do Sul.
One Low pressure area migrates on Thursday from Northeast Argentina to Rio Grande do Sul, generating strong instability in the three southern states with rain, which will be widespread and locally strong to intense, and isolated thunderstorms.
At Fridayat the beginning of the day, low pressure will be over Rio Grande do Sul and deepens, already with the cyclogenesis process, advancing towards the coast during the day, where further intensifies as an extratropical cyclonel which will have its center, estimated by the models at up to 995 hPa, very close to the South Coast of Rio Grande do Sul between Chuí and Rio Grande, over the Atlantic Ocean.
At the Saturdaythe cyclone will be over the Atlantic still close to the coasts of Rio Grande do Sul and Uruguay at the beginning of the day, even more intense and with pressure projected by various models between 980 hPa and 985 hPa, but over the period the system moves away from the continent in the East-Southeast direction while a high pressure center with colder air begins to take over southern Brazil.
The maps show the projection of precipitation and atmospheric pressure on the surface of the European meteorological model, based on the 0Z output this Wednesday, which shows how cyclogenesis will occur very close to the coastal strip and how intense the cyclone will be on the coast, The very close pressure lines in the east of Rio Grande do Sul are consistent with intense systems that bring strong wind.
We emphasize that It is not the proximity to the coast of a cyclone that determines its intensity, but rather its atmospheric pressure. One cyclone near the coast only increases the potential impacts on the continent. The lower the pressure at the center of a cyclone, the greater its intensity. Models indicate very low atmospheric pressure at the center of this system when it forms over the Atlantic Ocean.
Cyclone formation will bring intense rain
MetSul Meteorologia warns that the deepening of a low pressure center over Rio Grande do Sul with the subsequent formation of the extratropical cyclone over the Atlantic Ocean along the coast of Rio Grande do Sul will bring strong to intense rain and thunderstorms in many parts of southern Brazil between this Thursday and Friday. High volumes should be expected in several locations.
The map below shows the accumulated rainfall projection from the high-resolution WRF model until the end of Friday, in which the trend of rainfall above 100 mm in many places between the Northwest and North of Rio Grande do Sul, part of Santa Catarina and some areas of Paranásuch as the South and Southwest of the state.
The possibility of excessive and extreme precipitation accumulations in part of southern Brazil is of concern. The WRF model indicates the possibility of volumes of 150 mm to 200 mm with isolated accumulations of up to 200 mm to 250 mm or more in points between the Northwest of Rio Grande do Sul, the West of Santa Catarina and the Argentine province of Misiones.
Excessive rain could lead to floods, flash floods, landslides and falling barriers in these areas where accumulations tend to be higher. The biggest concern, however, is river levels. The volumes will be high in the Uruguay River basin and in others that cross the west of Santa Catarina and the southwest of Paraná, which have high levels and have had floods in the last few days.
Cyclogenesis will also bring strong storms
Also be warned to high potential for severe weather during the process of cyclone formation, cyclogenesis. Storms are expected to hit the three southern states and also places in the Central-West and Southeast of Brazil. Instability is already beginning to increase in the South of Brazil from the afternoon to the evening of this Wednesday with low pressure between the North of Argentina and Paraguay with rain in several parts of the region, but it tends to intensify further throughout Thursday with locally heavy rain and some risk of isolated thunderstorms.
A greater instability will occur on Friday, when the deep low pressure is over Rio Grande do Sul and migrating to the ocean, intensifying and giving rise to the cyclone. On Friday, the risk of severe weather is very high in southern Brazil. Colder air will be advancing over Northern Argentina while warm air will be east of the low pressure center, generating the cyclone and increasing the risk of severe weather.
Very heavy clouds will bring torrential rain, localized windstorms and hail during Friday in the three southern states. O The worst of the instability on Friday will occur in the Northern Half of Rio Grande do Sul, Santa Catarina and Paraná. Some Localized storms can be strong to severe with severe damage and the formation of tornadoes cannot be ruled out due to the sharp divergence of wind in the atmosphere.
See on the maps above the precipitation projection for Thursday night and the early morning, morning and afternoon of Friday based on the European Meteorological Center (ECMWF) model, which shows how intense instability will be in the south of the country during the cyclone formation process.
It cannot be ruled out formation of a pre-frontal squall line associated with cyclogenesis in southern Brazil with strong to severe storms at the end of Thursday and the beginning of Fridaywhich would worsen the potential for damage from severe weather.
The cold front associated with the cyclone as it advances to the North should stimulate isolated thunderstorms in isolated points in many areas of the Central-West and Southeast of Brazil between Friday and Saturday. As the cyclone will be intense and will form further north than usual, close to Rio Grande do Sul, the front will be able to reach the Northeast of Brazil with rain and storms as far as Bahia.
Cyclone will bring very strong to intense wind
A formation and subsequent action of the extratropical cyclone should bring a lot of wind to Uruguay and southern Brazill. The wind will occur in different phases and with different characteristics as synoptic conditions change in the mid-latitudes of South America.
Initially, the contrast between the low pressure between Northern Argentina and a high pressure center in the ocean will favor wind from the east quadrant moderate to strong in Rio Grande do Sul today and tomorrow with the most intense gusts this Thursday, when they can reach 60 km/h and 70 km/h in several cities in the Center-South and East of Rio Grande do Sul, including Porto Alegre. Therefore, it is not yet a cyclonic wind.
With the cyclone forming east of Chuí, the The wind will already be cyclonic on Friday and will blow moderate to strong in Uruguay, in many areas of southern Brazil and in Mato Grosso do Sul with gusts on average from 50 km/h to 80 km/hbut higher in sectors of the South and East of Uruguay as well as the South and East of Rio Grande do Sul, where they will be stronger with marks of 80 km/h to 100 km/h and higher alone.
On Saturday, with the cyclone beginning to move away from the continent, the wind will blow weaker in most areas, but will still be strong to intense at times between the early hours of the morning and mid-afternoon in the South and East of Rio Grande do Sul. The wind increases on the coast of Santa Catarina, especially between Passo de Torres and Florianópolis with gusts averaging 50 km/h to 70 km/h, but 70 km/h to 90 km/h on some beaches.
O The worst of the wind, according to MetSul’s analysis, should occur in the Uruguayan departments of Rocha and Maldonado, in the neighboring country, and on the South Coast of Rio Grande do Sul, between Chuí and Mostardas. In these areas, gusts of wind should reach marks in some places from 80 km/h to 100 km/h with individually higher speeds. At coastal area between Barra do Chuí, Hermenegildo and Rio Grande, on the South Coast, the gusts should be more intense with marks around 100 km/h, but could be between 100 km/h and 120 k/h in some points.
In Porto Alegre, wind gusts should be, on average, between 50 km/h and 70 km/h, from the initial moment with East wind on Thursday to the cyclonic wind between Friday and Saturday, but due to the city’s topography, stronger gusts may occur in some points. On the North Coast, gusts averaging 60 km/h to 80 km/h should be expected, although locally higher.
The strong gusts of wind associated with the cyclone can cause Falling trees, poles and structural damage, especially in the South and East of Rio Grande do Sul as well as on the Uruguayan coast. In the state of Rio Grande do Sul, the wind can still bring Electricity cuts with the biggest impacts in the CEEE Equatorial concession areasince the concessionaire operates in the South and East of Rio Grande do Sul, including the coastal strip.
The cyclone’s very intense wind field in the high seas will generate intense sea agitation with strong swellso that MetSul Meteorologia warns of the high risk of sea hangover on the coast of southern Brazilespecially on the coast of Rio Grande do Sul and Santa Catarina, with waves that can reach up to 4 or 5 meters.
The sea undertow on some beaches, such as the Rio Grande do Sul coast, can be strong with a risk of damage and coastal erosion. The activities of the Port of Rio Grande do Sul must be affected with impractical conditions at the port terminal. AND Navigation with small boats on the coast and in inland waters such as Lake Guaíba and Lagoa dos Patos is extremely inadvisable..
MetSul Meteorologia is on WhatsApp channels. sign up here to access the channel in the messaging app and receive forecasts, alerts and information about the most important events in the weather and climate in Brazil and around the world, with exclusive data and information from our team of meteorologists.