the season may be hotter than normal! Climate expert Paola Bueno explains to us

O autumn in Brazil has been quite anomalous in relation to the expected climatological pattern for the season. To the rains have been concentrated in the extremes of the countrysuch as in parts of the South, Northeast and North regions, regions that in fact tend to receive more rain during this period, but these rains have exceeded expected volumes, especially now in the South region, as we have been reporting.

About that, Much of central Brazil experiences an extremely dry period, with no significant rain and low relative humidity values. Result of the establishment of an atmospheric blockage which, in addition to preventing the formation of rain, has substantially increased temperatures, configuring a very atypical heat wave for this time of year. This makes us wonder: will winter follow this trend or can we expect a more severe cold pattern?

What ocean patterns could influence winter?

As we mentioned in a previous article, We are going through an El Niño-Southern Oscillation (ENSO) transition periodwith El Niño in its final stage and models indicating the emergence of La Niña during the winter and early spring.

While La Niña develops at a very slow pace, the positive phase of the Indian Ocean Dipole will take shape during the winter, potentially influencing the Brazilian climate during this season!

In fact, we will begin to observe the emergence of negative Sea Surface Temperature (SST) anomalies associated to La Niña over the Tropical Pacific throughout the winter quarter, however, the phenomenon should actually be established between the end of winter and beginning of spring, as ocean-atmosphere coupling may take time to occur. That way, we do not expect major effects of La Niña on Brazil during the winter.

Stopping looking at the Pacific and turning our eyes to the Indian Ocean, a well-known oceanic pattern has already taken shape there and is expected to form before La Niña: the positive phase of the Indian Ocean Dipole (DOI)! The last observed SST anomaly fields in the tropical portion of the Indian Ocean already show a difference in SSTs between the eastern and western portions of the basin.

Forecasts indicate that From May this difference in SST anomalies in the Indian Ocean will increase, configuring the positive dipole that should gain strength throughout the winter. The configuration of this dipole, despite being very far from Brazil, can generate anomalous wave patterns that modulate the patterns of troughs and crests over Brazil, consequently changing the intensity and positioning of low and high pressure systems.

What to expect from rain during winter in Brazil?

As we know, winter is the driest period of the year for much of Brazil, however, This winter could be drier than normal! The models have pointed out a trend of negative rainfall anomalies mainly over the Center-South of Brazil, as well as in parts of the Center-West and Southeast, in addition to the northern and western portions of the South region.

South region ends the week with a stationary front: warnings of very intense rain and high volume

One of the possible culprits for this rainfall deficit could be the positive phase of the DOI, which usually favors the establishment of atmospheric blocks over the Center-South. Often this type of blockage, very similar to the configuration that currently predominates, favors the convergence of humidity over the extreme south of Brazil, in addition to restricting the action of frontal systems, causing parts of the South, such as the state of Rio Grande do South, receive large volumes of rain in a few days.

Therefore, even if there is not a very intense signal of positive precipitation anomalies in the model predictions – with a slightly more evident signal on the coast of the South region in June – there is the possibility of extreme rain events occurring in the southern region at certain times of winter.

Heavy rains than normal may also occur in the extreme north of Brazil, also due to the action of the Intertropical Convergence Zone (ITCZ) driven by the warmer than normal waters of the tropical Atlantic. In some areas of the east coast of the Northeast We can also expect above-normal rainfall, but these anomalies will be less intense and widespread.

And what to expect from the temperatures?

As mentioned, we do not expect the influence of La Niña in the winter of 2024, which could favor the entry and action of polar air masses that would drop temperatures, making the next winter more “rigorous”. However, looking at the forecast maps for the months of June, July and August, we see a very opposite scenario, with positive temperature anomalies being predicted for much of Brazil!

To the Temperatures are expected to be above normal, especially in the Center-South of Brazil, which may also be associated with a greater occurrence of atmospheric blockages due to the action of the positive phase of the DOI. Although, This does not mean that we will have a winter with several days in a row of very hot and exceptionally high temperatures. Hotter periods can be interspersed with colder days, with the presence of cold air masses. But in any case, the tendency is that we will have a winter with average temperatures above normal.