Winter begins this week in the Southern Hemisphere

Winter in the Southern Hemisphere begins on June 21, 2023, at 11:58 am, and ends on September 23, at 3:50 am (Brasília time). Climatologically, the season is marked by a less rainy period in the Southeast, Central-West and parts of the North and Northeast of Brazil. On the other hand, the highest volumes of precipitation (rain) are concentrated in the northwest of the North Region, east of the Northeast and in part of the South of the country (figure 1a).

The reduction in rainfall in a large part of Brazil at this time of year is due to the persistence of dry air masses, which causes a decrease in relative air humidity and, consequently, favors the occurrence of fires and forest fires, as well as an increase in of respiratory diseases.

In addition to the lower incidence of solar radiation, the season is also characterized by the incursions of cold air masses coming from the south of the continent, causing a drop in air temperature and average values ​​below 22ºC in the eastern part of the South and Southeast regions of Brazil (figure 1b).

The decrease in temperature can cause: i) formation of frost in the South and Southeast regions and in the state of Mato Grosso do Sul; ii) snowfall in mountainous areas and plateaus in the South Region and, iii) episodes of cold weather in MatoGrosso, Rondônia, Acre and southern Amazonas. Furthermore, in winter, due to thermal inversions in the morning, it is common for fog and/or humid fog to form in the South, Southeast and Central-West, with reduced visibility, especially on roads and airports.

El Niño

In the Equatorial Pacific Ocean, the monthly averages of the Sea Surface Temperature (SST) of the reference area for defining the El Niño Southern Oscillation (ENSO) event, called the Niño 3.4 region (between 170°W-120°W), recorded SST anomaly values ​​lower than -0,5°C from August 2020 to January 2023, indicating a long period under the influence of the La Niña phenomenon.

In March of this year, the end of the La Niña phenomenon was confirmed after three years of duration, indicating the beginning of neutral conditions. However, between April and May, it was possible to notice a rapid warming of the waters of the Equatorial Pacific, extending from the west coast of South America to the central part of the Equatorial Pacific basin. Furthermore, coupling conditions between the ocean and the atmosphere have intensified in recent weeks, confirming the onset of the El Niño phenomenon, as declared by the United States National Oceanic and Atmospheric Administration (NOAA) this month.

Several models indicate a high probability of El Niño persistence in the coming months. The forecast from the APEC Climate Center (APCC) model, a research center based in South Korea, points to a probability of over 90% of El Niño conditions remaining in winter/2023, with a chance of lasting until spring/ 2023. Furthermore, the model also indicates that the phenomenon may vary in intensity, ranging from moderate to strong (figure 2).

To check the Climate forecast for July, August and September/2023 in the regions of Brazil, click here.