An extratropical cyclone, a meteorological phenomenon responsible for strong rain and winds, is affecting parts of Brazil this week, with the greatest impact between August 10th and 11th in the states of Paraná, Santa Catarina, Minas Gerais, São Paulo and Rio de Janeiro. 

Extratropical cyclones, common in Brazil's climate history, generally form in the extreme south of the country, between Rio Grande do Sul and neighbors Argentina and Uruguay. Their winds are weaker and their effects are shorter than tropical cyclones.

Extratropical cyclones form in the Atlantic Ocean every week, sometimes dozens of them. But it is common for them to form near the South Pole, very far away. That's why we don't mention it in the weather forecast – an extratropical cyclone 1,000 kilometers from the coast will not affect the population, explains Estael Sias, meteorologist at MetSul, a meteorological content platform.

The difference between the phenomenon we are seeing now, explains Sias, is its area of origin, which is between the states of Santa Catarina and São Paulo, and the proximity to the Atlantic coast, which the population feels.

Formation is not as fast as, for example, a tornado, which occurs in a few minutes. Authorities have been monitoring the phenomenon for five to seven days, says Ana Ávila, meteorologist and researcher at Unicamp (State University of Campinas).

There is a risk of flooding, landslides and flash floods, as well as roofing, damage to electrical networks and falling trees and branches. The risks vary depending on the region and the intensity with which the cyclone is expected to affect. For this reason, it is important to always be aware of the recommendations of civil defense and other responsible bodies in your city and state.

An example is the difference in wind gust strength between Florianópolis and the city of São Paulo. Further south, the wind is said to reach 100 km/h. In São Paulo, it is said that the strongest gusts range between 60 km/h and 80 km/h.

The CGE-SP (São Paulo Emergency Management Center) advises anyone staying in the city of São Paulo to stay away from power lines, under trees and not to move.

In cities in the south of the country with an increased risk of flooding, recommendations from responsible bodies range from finding safe shelter to avoiding contact with water.

Coastal cities are also expected to feel a greater impact. The winds are stronger near the sea, as are the waves, which can reach four meters in height. Therefore, it is crucial that all maritime activities such as fishing cease. The risk is very high, as shown by weather alerts from civil defense, especially in the last 24 hours, explains Ávila.

Extratropical cyclones are centers of low atmospheric pressure that form outside the tropics in middle and high latitudes.

It is created by the contrast of hot and cold air masses. Part of its action is to suck all the moisture into this region of the low pressure center and expel it into the atmosphere, cooling the moisture and turning it into clouds. In this process, the phenomenon spreads rain and wind, says meteorologist Estael Sias.

In the hardest hit areas, recommendations call for more caution. Below is an example of the advice given by Civil Protection of Santa Catarina:

Flooding 

Landslides 

Pay attention to: 

Strong wind 

Find a sheltered location away from trees, signs, posts and other objects that could be thrown; 

Stay away from windows in a sheltered place.

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