Brazil's MetSul weather agency believes that La Nina has finally developed in the Pacific Ocean after months of anticipation and an unusually delayed onset. According to MetSul, the US National Oceanic and Atmospheric Administration (NOAA) is about to officially declare La Nina, possibly this January.
It is quite unusual for a La Nina event to begin or be declared in January. If confirmed, this would be the latest onset of a La Nina observed in the past 50 years.
La Nina is defined as a combination of ocean and atmosphere patterns in the tropical Pacific Ocean. La Nina is a phenomenon in which the surface water of the tropical Pacific Ocean is at least 0.5 degrees Celsius cooler than the long-term average (1991-2020) accompanied by changes in the Walker atmospheric circulation.
These atmospheric signals include stronger winds in the upper and near-surface levels (trade winds) in the tropical Pacific, more than normal rainfall in Indonesia, and less rainfall in the central Pacific – all of which have been observed in recent weeks.
For a La Nina event to be declared, both the ocean and the atmosphere must exhibit these changes, as their interaction helps La Nina form and persist for months. Therefore, there are two necessary criteria: ocean and atmospheric indicators.
Although atmospheric conditions have shown signs of La Nina, initial sea surface temperature anomalies were not consistent with the phenomenon. However, in recent weeks, sea surface temperatures have dropped by 1.1 degrees Celsius, indicating the onset of La Nina.
Unlike the La Nina event that lasted from 2020-2023, this phenomenon is predicted to be weaker and shorter, lasting only about 3-5 months. NOAA forecasts show that the probability of La Nina occurring in the period from January to March 2025 is estimated at 63%; from February to April is 51%; from March to May is 32%; from April to June is 29%; from May to July is 27%, while El Nino is 10% during the same period.
For Vietnam, in January and spring, La Nina could bring more than average rainfall, especially in the Central and Central Highlands regions. The risk of flash floods and landslides could increase. At the same time, the North could experience longer-than-normal cold spells, while the South is likely to experience cooler weather and unseasonal rains.
Scientists say that although La Nina may appear to cool global temperatures slightly by 2025, the planet is still warming at an alarming rate.
According to European scientists, 2024 is set to be the hottest year on record and the first to see global average temperatures surpass the Paris Agreement target of 1.5 degrees Celsius above pre-industrial levels.
According to analysis of data from the World Meteorological Organization, the high temperatures in 2024 are partly due to El Nino climate conditions.
