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MetSul Meteorology warns of unusual weather in Brazil until the end of May, with above-average rainfall in São Paulo, Rio de Janeiro, Paraná, and Minas Gerais, significant heat in the central part of the country, and a new polar air mass bringing frost to the South. El Niño is about to set in and is expected to change the Brazilian climate.
On May 17, 2026, Sunday, MetSul Meteorology published an analysis warning of a weather pattern outside the historical average in Brazil until the end of the month, with a strong impact on the Southeast, Midwest, and South of the country. According to meteorologist Estael Sias, author at MetSul and master in Meteorology from USP, above-average rainfall is expected in states like São Paulo, Rio de Janeiro, Paraná, South of Mato Grosso do Sul, and South of Minas Gerais, significant heat in areas of Goiás, Tocantins, Mato Grosso, and in Minas Gerais, and a new polar air mass advancing over Rio Grande do Sul, Santa Catarina, and part of Paraná, with frosts expected mid-week.
The warning is especially relevant because May usually marks the transition from the summer rainy season to the typical dry season of autumn and winter in Central and Southeast Brazil. Instead of the rain naturally decreasing at this time of year, the models from the European Centre for Medium-Range Weather Forecasts (ECMWF) project high volumes where it should be raining little. This unusual weather coincides with the imminent formation of a new episode of El Niño, which the United States National Oceanic and Atmospheric Administration (NOAA) classified on May 14 as an official alert, with an 82% probability of formation between May and July 2026.
Why the weather deviates from the historical pattern in May in Brazil
The atmosphere undergoes gradual changes that reduce the frequency and intensity of precipitation. The main reason is the weakening of moisture corridors coming from the Amazon, known as atmospheric rivers, which during the summer feed frequent storms in the Midwest and Southeast with strong vertical development.
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With less heat and lower availability of moisture, the formation of convective clouds decreases, those responsible for the typical late afternoon showers. The atmospheric circulation also changes with the more frequent advance of cold air masses through the South of Brazil and the ocean, favoring longer periods of stability. In 2026, however, this stable climate is not being confirmed: rainfall volumes are already above the historical average in capitals like São Paulo and Belo Horizonte, according to data from surface stations.
Rain above average in São Paulo, Rio de Janeiro, Paraná, and Minas Gerais
The numbers show the difference from the pattern. At the Mirante de Santana station, in the northern zone of São Paulo city, the accumulated rainfall between May 1st and 17th, 2026 reached 50.4 millimeters, against a historical average for the entire month of 66.3 millimeters, according to data published by MetSul. As there are still days with rain forecast on the calendar, May is expected to close with São Paulo’s capital having a volume higher than the climatological average.
In Belo Horizonte, the Cercadinho station had already accumulated 30.2 millimeters by the morning of May 17th, surpassing the climatological average for the month, which is 28.1 millimeters. The positive deviation is expected to increase with what is still expected in precipitation until the end of the month, and the largest deviations should occur in the South of Minas Gerais. The atypical climate is also expected to affect areas further north of Paraná, the South of Mato Grosso do Sul, the state of São Paulo, the South of Minas Gerais, and Rio de Janeiro, according to the European model projection.
Strong heat in the Center of Brazil and contrast with the South
While the Southeast and South receive above-average rainfall, the Center of the country is heading for temperatures well above what is expected for the end of May. The ECMWF temperature anomaly maps indicate that the last week of the month should be marked by intense heat in Goiás, Tocantins, Mato Grosso, and Minas Gerais, with significant positive deviations from the historical average for the period. Cities in these regions may record afternoons with temperatures close to or above 35 degrees in the late autumn.
This heat is especially atypical because the second half of May usually signals the beginning of the so-called “veranico,” with mild afternoons and already cool nights. In 2026, however, the climate is expected to maintain low humidity, dry vegetation, and potential for wildfires in rural and cerrado areas, in a risk window that tends to extend over the coming months, as meteorologists monitoring the transition to the new El Niño episode in the Equatorial Pacific warn.
New polar air mass advances over the South with frosts during the week
In the South of Brazil, especially in Rio Grande do Sul, the scenario is the opposite. A new cold air mass began to enter the state at the beginning of the week of May 19th, with a reinforcement of polar air expected for the middle of the week. The combination is expected to result in several consecutive days with negative temperatures, frost, and a wind chill close to zero in municipalities in the regions of Serra, Campanha, and Campos de Cima da Serra, according to MetSul.
The polar air also advances over Santa Catarina and part of Paraná, with the possibility of frost in the plateaus of Santa Catarina and Paraná. From the end of the week, the cold air mass begins to lose strength, with a gradual rise in temperature, but the nights should remain cold and the afternoons mild in the South, without any heat records. For those who live or work in these states, the cold weather requires extra care with agricultural activities, especially those aimed at the production of vegetables, fruit trees, and pastures sensitive to frost.
El Niño is about to settle in and is expected to change Brazil’s climate
In parallel to this scenario of occasional extremes, MetSul points out that the start of a new El Niño episode is considered imminent. MetSul’s analysis, based on oceanic and atmospheric data, indicates that the phenomenon should begin to settle between the end of May and June 2026. This diagnosis is in line with the official NOAA report released on May 14, which raised the status to El Niño alert, with an 82% chance of formation between May and July and 96% for the quarter between December 2026 and February 2027.
The National Institute of Meteorology (INMET), in a technical note from April, also confirms the trend. According to the agency, the probability of El Niño exceeds 60% in the May-June-July quarter and may exceed 90% in the second half of the year. The Brazilian climate is expected to feel the effects gradually between June and July, with intensification throughout the second half of the year. The expected consequences include a significant increase in rainfall in the South, with the risk of floods and storms, a reduction in rainfall and worsening drought in the North and Northeast, and a higher frequency of heat and wildfires in the Southeast and Midwest.
What to expect from the climate in the coming months in Brazil
The scenario projected by meteorology for 2026 reinforces the importance of citizens keeping up with updates from official agencies. For the South, INMET models indicate above-average rainfall already in the May-June-July quarter, with a direct effect on cities in lowland areas, especially in Rio Grande do Sul, still recovering from extreme events recorded in previous years. For the Midwest and Southeast, the signal is for reduced humidity and above-normal heat in the driest months.
For the North and Northeast, the trend of decreasing rainfall tends to intensify from mid-year, with a direct impact on the reservoir levels of the Amazon and on the rainfed agriculture of the northeastern semi-arid region. In all cases, experts emphasize that the climate under the influence of El Niño is more prone to extremes, with short time windows between opposing events, which requires planning by civil defenses, rural producers, and the energy generation sector, which depends on rain to supply hydroelectric plants.
The alert from MetSul for the end of May is just the first chapter of a climate scenario that promises to be challenging in Brazil throughout the second half of 2026. Rain where there is usually little, heat where it was supposed to cool down, and polar cold in the South draw a map of contrasts in just a few weeks. Those working in agriculture, transportation, energy, civil defense, and construction need to pay extra attention, because El Niño tends to amplify all of this starting in June.
Have you felt the weather different in your state in recent weeks? Do you think Brazil is prepared to face a new episode of El Niño, with possible floods in the South and drought in the North and Northeast? Leave your comment, tell us how the weather is in your city at the end of May, and share the article with those who need to prepare for the extremes expected in the coming months.
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