The Civil Defense of Rio Grande do Sul has issued an alert regarding the possibility of storms in the state between Thursday, the 16th, and Saturday, the 18th. The forecast points to intense rain, wind gusts, and potential hail in several locations, with the greatest impacts expected for the night of Friday, the 17th, and Saturday morning.
Although the instabilities are expected to primarily affect the Western, Campanha, and Southern regions of Rio Grande do Sul, the projection indicates that severe conditions may advance to almost the entire state territory, including the Metropolitan Region of Porto Alegre. Accumulated precipitation volumes could reach 150 millimeters, with periods of very concentrated rain.
The formation of these storms is linked to a combination of atmospheric factors, notably the action of the Low-Level Jet (LLJ). This is an intense flow of winds that transports heat and humidity from the Amazon to the South-Central part of South America. Under certain circumstances, this moisture flow can intensify or generate atmospheric rivers, which are defined by the transport of large amounts of water vapor through the atmosphere.
The Low-Level Jet consists of a current of winds located between about 1 and 3 kilometers in altitude, traversing the interior of the South American continent. This system moves large volumes of warm and humid air, creating conditions favorable for the emergence of storms when it interacts with other weather patterns. The National Institute of Meteorology (Inmet) explains that the interaction between this moisture corridor and cold fronts coming from the south increases the concentration of water vapor and atmospheric instability, favoring heavy rains and more structured storms.
In a note sent to BBC News Brazil, Inmet stated: 'When the LLJ interacts with frontal systems coming from the south of the continent, there is an increase in moisture convergence and atmospheric instability, favoring the occurrence of severe storms.'
The National Center for Monitoring and Alerts of Natural Disasters (Cemaden) also signaled the possibility of significant rainfall accumulations. Marcelo Seluchi, general coordinator of Operations and Modeling at Cemaden, reported that a cold front should remain over the area for several days, sustaining the pattern of prolonged rain. However, the specialist emphasized that despite the influence of so-called flying rivers, the transport of moisture coming from the Amazon tends to be lower during winter due to lower temperatures and less availability of water vapor.
Besides Brazil, Chile may also suffer consequences related to an atmospheric river in the Pacific Ocean. According to MetSul Meteorology, this system may reach high intensity, causing extreme rain, strong winds, storms, and snow in the Andes Mountains. The Chilean areas considered most susceptible include Coquimbo, Valparaíso, Metropolitana, O’Higgins, Maule, Ñuble, and Biobío.
Atmospheric rivers are vast bands of water vapor that move through the atmosphere, typically originating in tropical zones and moving towards higher latitudes. Although invisible to the naked eye, these corridors can be detected by satellites using specific observation frequencies. These systems are responsible for transporting about 90% of the water vapor circulating in the planet's mid-latitudes. While low intensity can help with the water balance of certain regions, more powerful versions have the potential to cause floods and landslides.
In South America, part of these moisture corridors originates from evaporation in the Amazon Forest. When encountering the natural barrier of the Andes Mountains, the flow is diverted to places such as Central-West, Southeast, and South Brazil, as well as neighboring countries. Such mechanisms are crucial for the continental rainfall regime, as the transported moisture sustains ecosystems and agricultural activities, but it can also exacerbate extreme events when combined with other climatic conditions.
Deniz Bozkurt, a meteorologist from the University of Valparaíso in Chile, clarified that Amazonian atmospheric rivers are influenced by other elements, such as the equatorial rain belt, trade winds, and the Andes Mountains. He explained to BBC News Brazil: 'These elements together can guide the moisture, making it travel south, leading to heavy rains and floods in other regions.'
Experts point to the destruction of the Amazon Forest as a major concern for this climate system, since the decrease in vegetation cover can reduce the amount of available water vapor and impact moisture circulation in various parts of South America. Research also indicates that rising global temperatures have increased the amount of vapor in the atmosphere in recent decades, which can make atmospheric rivers more intense and increase the capacity of these systems to concentrate large volumes of rain in short intervals.
The railway operator of Uzbekistan, Temiryo'lexpress, has announced the temporary introduction of speed restrictions on certain sections of its railway network due to abnormally hot weather.
This measure is aimed at ensuring passenger safety and the uninterrupted operation of trains, as well as maintaining the stable functioning of the railway infrastructure during periods of high temperatures.
According to the operator, the restrictions will be in effect on selected sections of the railway where enhanced monitoring of track and infrastructure condition is required during the heat. As a result of these temporary speed limitations, some passenger trains may arrive at their destination later than scheduled.
Temiryo'lexpress has urged passengers to take into account possible changes in train arrival times and asked for understanding regarding the implemented measures, which are necessary to ensure the safety of rail transport.
A cold front will continue to affect the weather in Brazil between Thursday, the 16th, and Friday, the 17th. According to Inmet, the forecast points to rain, strong winds, and falling temperatures in various regions.
While the South of the country returns to the risk of storms, the Northeast will maintain rain on the coast. On the other hand, the Southeast and much of the Central-West are expected to have stable weather and low humidity.
The combination of a low-pressure area located over Argentina and another high-pressure area in the Atlantic Ocean strengthens the Low-Level Jet (LLJ). This system enhances the transport of heat and moisture, generating conditions favorable for the formation of new instabilities.
Rio Grande do Sul is the main highlight. On Thursday (16th), rain accompanied by thunderstorms is expected in the south and west of the state. The following day, instabilities will spread throughout almost all of the state's territory, except for the far north and the rest of the Southern Region, which should remain dry.
The main warnings issued include a yellow alert for storms in Rio Grande do Sul on Thursday and in almost the entire region on Friday. Additionally, there is a yellow alert for strong winds in western Paraná, western Santa Catarina, and Rio Grande do Sul on Thursday, escalating to an orange alert in these same areas on Friday. There is also a possibility of frost between dawn and early morning in southern Paraná.
On the eastern strip of the Northeast, the cold front continues to bring rain showers, affecting states such as Bahia, Sergipe, Alagoas, Pernambuco, Paraíba, Rio Grande do Norte, Ceará, Maranhão, and much of Piauí. The next day, the intensity of precipitation decreases, concentrating between the coast and the Agreste. In northern Maranhão, there is still a chance of thunderstorms, while the interior of the region should have clear skies, maintaining yellow alerts for heavy rain and strong winds in parts of the coast.
The scenario in the Southeast presents predominantly clear skies, but frost is predicted in southern Minas Gerais, Campos do Jordão (SP), and the mountainous areas of Resende (RJ). In the higher parts of Southern Minas and Campos do Jordão, minimum temperatures may reach around 3°C, and parts of São Paulo and Minas Gerais remain under a low humidity alert.
In the North, isolated rains persist and strengthen on Friday in Roraima, Acre, Amazonas, Amapá, and in the northern and western parts of Pará. Tocantins and southeastern Pará are expected to have clear skies. In the Central-West, Mato Grosso has the highest probability of rain, especially in the northern and western regions. The Pantanal of Mato Grosso do Sul may record scattered precipitation, while Goiás, the Federal District, and part of Mato Grosso do Sul stand out for the low air humidity.
In summary, while the South deals with risks of strong winds, rain, and storms, other regions face morning frosts, low humidity, and warmer afternoons. This contrast will define the country's meteorological outlook until Friday, according to Inmet information.
