Warning of serious risk of flooding due to extreme rain in southern Brazil

Excessive and extreme volumes of rain should be expected in the second half of this week in part of southern Brazil, warns MetSul Meteorologia. Very high rainfall accumulations are expected to lead to floods, river floods and flash floods. The situation can be considered extremely risky and dangerous, considering the extreme volumes and where they should occur, over some of the main hydrological basins.

An exceptionally hot air mass continues to act as a heat bubble over the Central-West and Southeast of Brazil with historic and unprecedented temperature marks in some cities. This bubble of superheated air is directly related to the anticipated extreme rain event.

This is because the bubble blocks instability and it rains a lot on the periphery of the superheated air mass, that is, over the southern states of Brazil. This situation leads to several days in a row with rainfall recorded, which ends up resulting in excessively high rainfall accumulations.

That wasn’t enough, and what’s more worrying, the excessive rain expected for this second half of the week adds to the already very high volumes that have occurred in recent days. In the last five days, for example, it rained more than 100 mm in several cities in the Northern Half of Rio Grande do Sul, with records, for example, of 127 mm in Serafina Corrêa and 117 mm in Caxias do Sul.

Conditions are high risk of heavy to intense rain between the Northern Half of Rio Grande do Sul and Santa Catarina today, tomorrow, Friday and Saturday. Over the weekend, especially on Sunday, the tendency is for instability to migrate to the North and the weather to improve in the states of Rio Grande do Sul and Santa Catarina.

An area of ​​deep low pressure followed by a cold front will greatly intensify instability in southern Brazil between Friday and Saturday, increasing the potential for locally heavy rain to torrential with the possibility of very high volumes of precipitation in a short period.

MetSul Meteorologia also warns that the same strong to intense instability that will bring a lot of rain between the Northern Half of Rio Grande do Sul and Paraná during this second half of the week could also cause isolated storms of wind and hail, some potentially strong to severe damage, but always at localized points.

What the models project from rain

Numerical models are unanimous in indicating excessively high volumes of rain for this second half of the week in southern Brazil. It is of great concern that it is indicated for the Northern Half of Rio Grande do Sul, where the accumulations should be extreme in some points with marks of 200 mm to 300 mm in some cities only between today and the end of Friday.

The model projections are very similar in the special distribution of rain with the highest rainfall accumulated until the weekend concentrated in the Northern Half of Rio Grande do Sul, Santa Catarina and Paraná. The variations are only in volumes from one location to another, but always very high. The maps below show rainfall projections for five days from the German Icon, Canadian CMC and European Meteorological Center models.

METSUL METEOROLOGY

The models’ indication, as can be seen, is volumes of 100 mm to 200 mm in almost the entire Northern Half of Rio Grande do Sul and part of Santa Catarina, but with points where rainfall accumulations can reach marks as high as 200 mm at 300 mm, that is, almost two months of rain in just five days.

The Southern Half of Rio Grande do Sul would escape this episode of excessive rain with much smaller rainfall accumulations, but it has already rained a lot with marks of 100 mm to 150 mm in the South of Rio Grande do Sul between the end of last week and the beginning of this one.

Flood warning

With what has already rained and precipitation is still expected for this week, MetSul warns of significant impacts for the population and, in some municipalities, serious ones. Cities will experience floods and floods again, repeating the scenes of recent weeks and months in southern Brazil.

What is of great concern, especially in Rio Grande do Sul, is that excessive and extreme volumes of rain are expected to occur over the sources of the main rivers in the Northern Half of Rio Grande do Sul. This leads us to warn of a high risk of flooding in rivers that cross valleys such as the Taquari-Antas and Caí. Sinos can also be full. Gravataí has ​​lower risk. It should still rain a lot in the Jacuí springs and, especially, in the beginning of the Uruguay River basin.

Rain with accumulations as extreme as expected also brings geological risks. The risk of landslides in hillside areas will be very high. There must also be barriers falling that could result in partial or total blockages of state and federal highways.

Some roads, particularly municipal and rural ones, are expected to become impassable with likely sections and ridges covered by water. With the prospect of strong currents, flooded sections should be strictly avoided by drivers at risk of fatal accidents.

How to consult the maps

All rain maps in this bulletin can be consulted by our subscribers (subscribe here) in our maps section. The platform also offers maps of rain, frost, temperature, risk of hail, wind, humidity, atmospheric pressure, snow, soil moisture and risk of fire and lightning, among other variables, with updates two to four times a day, depending on with each simulation. In the maps section, you can also consult our very high resolution WRF model of MetSul.

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