Responsible for the increase in temperatures in the city of São Paulo, which make them the highest level of the year, the heat wave which has hit eight Brazilian states since December 23 has led the National Institute of Meteorology (Inmet) to issue a “Great Danger” alert due to health risks. Able to cause thermometers to record up to 5°C above what is expected for the period, the heatwave is caused by a high-level cyclonic vortex (VCAN).
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This involves the formation of intense high-altitude winds that rotate clockwise. The VCAN helps maintain a dry air mass over part of the country by promoting atmospheric blocking, thus preventing the advance of a cold front. In regions located on the outskirts of the vortex, the effect is the opposite, with greater chances of rain.
— Generally, these heat waves occur more frequently in January and also in winter, September, August, September — explains meteorologist Andrea Ramos. — We have a cyclonic vortex favoring atmospheric blocking. Cyclones are linked to low pressure. But VCAN is at high levels. Thus, below, this mass (of hot air) forms because its center is dry, characteristic of high pressures. In the periphery, there is instability.
Inmet has issued two alerts for the heatwave. The first of these, classified as “Great Danger”, affects Rio de Janeiro, São Paulo and parts of Minas Gerais, Paraná, Goiás, Santa Catarina and Espírito Santo. The second, “Potential Danger”, extends from the coast of Espírito Santo to the central part of Goiás, including Goiânia. Belo Horizonte is also in the area of this alert. Both are valid until the 29th.
At the end of November, when publishing the forecast for the month of December, Inmet had already highlighted the tendency for temperatures to be above average in almost the entire country. According to the institute, the largest increases would be concentrated in the North, the Northeast and the Center-West. Only in the South, some regions would go as planned.
Despite the phenomenon, rain is forecast for the coming days, specifies meteorologist Andrea Ramos.
— Models are already showing signs of isolated rain Saturday, part of Saturday, and getting heavier over the next few days. There will still be some erratic rain, but it will reach the areas where this heatwave is located. Especially because we have humidity.
In the case of Rio de Janeiro, Climatempo highlights the possibility of rain showers starting Monday, which will continue the next day. In São Paulo there is a risk of precipitation in the afternoon this Friday. Over the weekend, afternoon and evening showers continue in the capital São Paulo.
São Paulo, as well as parts of Goiás, Minas Gerais, Paraná and Mato Grosso do Sul, appear both in the heatwave zone and in a yellow warning, of “potential danger”, for the appearance of storms. According to Inmet, precipitation can reach up to 50 mm/day, with intense winds between 40 and 60 km/h. There is a small risk of power outages, crop damage, falling tree branches and flooding.
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