September begins with a stark contrast between rainfall and temperature.

The forecast for September indicates above-average rainfall and incursions of cold air in the Central-South region of Brazil, while the North and Northeast are expected to face above-normal temperatures and below-average precipitation. This scenario marks a stark climatic contrast in the country at the start of the meteorological spring, which begins on September 1st.

The monthly precipitation anomaly forecast from the ECMWF model, trusted by Meteored, points to a strong contrast between Brazilian regions throughout September. In the Center-South, rainfall is expected to be above average across much of the area. In the North, however, volumes are expected to be below normal, while the Northeast coast is likely to experience slightly below-average precipitation.

The largest negative deviations in precipitation, up to -50 millimeters, are predicted for an area on the border between Amazonas and Pará. Below-average values are also expected in practically the entire North region. On the northeastern coast, the forecast indicates rainfall slightly below average, while in the rest of the region, volumes should be close to the historical average.

The weekly forecast indicates that, in the first half of September, the largest positive deviations in precipitation should be concentrated between northern Rio Grande do Sul and Central Brazil. A wide area with weekly anomalies exceeding 50 millimeters should extend across the Southeast, Midwest, and southern part of the North region.

In the second half of the month, the largest positive deviations will again be concentrated in the South and nearby areas, including southern Mato Grosso do Sul and São Paulo. Even so, above-average rainfall is still expected over Central Brazil as well.

At the beginning of the month, the Northern region may still experience areas with above-average rainfall. In the first half of the month, positive deviations should appear mainly in the south of the region, also reaching the western half during the second week. Throughout September, however, water deficit conditions tend to expand and predominate in most of the northern states.

Along the Northeast coast, the pattern is also expected to fluctuate. The forecast indicates a shift from below-average rainfall to above-normal volumes during the first two weeks of the month. In the second half of the month, however, below-average rainfall is expected to predominate again along the coast. In other areas of the Northeast, rainfall is expected to be close to average.

The temperature anomalies predicted for September partly follow rainfall patterns. While the drier areas of the North and Northeast are expected to experience above-average temperatures, regions with higher rainfall tend to have temperatures closer to normal.

The largest temperature deviations are predicted for the area between Amazonas and Pará, precisely where the greatest negative rainfall anomalies are also expected. In the Northeast, monthly anomalies may exceed 2°C above average, while in the North, deviations may exceed 4°C.

The weekly temperature forecast from the ECMWF model indicates the distribution of anomalies throughout the month and reinforces the scenario of a higher frequency of frontal systems over the South-Central region.

In the first half of the month, cold air incursions should contribute to below-average temperatures in parts of the region. In the second half of September, however, the cold anomalies should weaken and give way to temperatures closer to the average in the South-Central region.

In the North and Northeast, on the other hand, above-average temperatures are expected to prevail throughout the month. The largest deviations, exceeding 4°C, are predicted for the first week of September. Although they will decrease slightly in the second week, the warm anomalies are expected to expand again and intensify from the second half of the month.

The forecast for September suggests a strong influence from El Niño and the frequent activity of frontal systems over the Central-South region of Brazil. According to the scenario presented by Meteored, the main mechanisms of intraseasonal variability do not show robust signs of activity on the scale analyzed.

The Madden-Julian Oscillation (MJO) is expected to remain weak and disorganized, while the Antarctic Oscillation (AAO) tends to oscillate around neutrality. Therefore, the above-average rainfall pattern and cold air incursions expected for the South-Central region should be determined primarily by the combination of El Niño and mid-latitude systems.

The predicted scenario for the first month of the meteorological spring is one of strong climatic contrast between Brazilian regions. In the Center-South, the combination of frequent frontal systems and the influence of El Niño should favor rainier periods and incursions of cold air.

In the North and Northeast, the scenario is the opposite, with above-average temperatures and a tendency for reduced rainfall, especially in the Amazon region. For agriculture, the irregular distribution of rainfall and temperatures throughout the month reinforces the importance of monitoring the evolution of meteorological conditions in the different producing regions.