A majority of global climate models have hinted at the likely re-surfacing of La Nina conditions during the upcoming winter months over the northern hemisphere. At least three models — Bureau of Meteorology (BoM) by Australia, National Centers for Environmental Prediction (NCEP) by National Oceanic and Atmospheric Administration and the Columbia Climate School International Research Institute for Climate and Society (IRI) — in the US — indicate a 70 to 80 per cent possibility of a borderline or weak La Nina conditions to re-emerge during the winter months of the northern hemisphere. Accordingly, the BoM has entered the ‘La Nina watch’ stage since last week.
La Nina is an ocean phenomenon, wherein the sea surface temperatures along the equatorial Pacific Ocean slip below normal. Due to such cool ocean temperatures, La Nina is known to favour Indian summer monsoon, make winters harsher over India and favour development of more cyclones that cross Indian coasts. According to the model suggestions, there are strong chances for La Nina conditions to start developing from October and these could prevail till the end of the winter season over the northern hemisphere.
However, the India Meteorological Department (IMD), in its El Nino Southern Oscillation (ENSO) bulletin for September, has ruled out the possibility of La Nina conditions. It has stated that the prevailing ENSO neutral conditions would last for the next few seasons. Like the IMD’s forecast, the Japan Meteorological Agency, too, has forecast neutral ENSO during the upcoming winter season.
“Though many global models are indicating re-emergence of La Nina conditions, some models do not favour it. Even if La Nina conditions do develop, they may not sustain for a long period as the required cooling, at present, is insufficient,” said O P Sreejith, head, Climate Monitoring and Prediction Group at IMD, Pune.
Using model predictions, the ENSO update issued by the World Meteorological Organisation mentions that ENSO neutral conditions will last till November and there are higher chances of La Nina conditions to develop during December and February next year. 2020 – 2021 was a La Nina year. The peak cooling associated with La Nina was recorded in November last year. Thereafter, the cooling showed a continuous declining trend and it ultimately reached the ENSO neutral condition during May this year. Since then, neutral conditions have lasted till August.