US weather agency cuts chances of La Nina emerging before December

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The Climate Prediction Centre (CPC), an arm of the US National Oceanic and Atmospheric Administration (NOAA), has further cut the chances of La Nina emerging before December. It expects the weather event, which brings heavy rainfall to India and other parts of Asia, to persist through January-March 2025.

In its latest update, CPC still maintained a La Nina watch, though the chances have been lowered to 57 per cent from 60 per cent last month and 66 per cent earlier.

In contrast to CPC’s prediction, Australia’s Bureau of Meteorology said earlier this week that La Nina is unlikely to emerge until February 2025.

Shorter duration event?

“The IRI (International Research Institute for Climate and Society) plume predicts a weak and a short duration La Niña, as indicated by the Niño-3.4 index values less than -0.5C. The latest North American Multi-Model Ensemble (NMME) forecasts are cooler than the IRI plume and predict a weak La Niña,” the US weather agency said. 

Due to La Niña-like atmospheric circulation anomalies over the tropics, “the team still favours the onset of La Niña”, but it is likely to remain weak and have a shorter duration than other historical episodes, it said. 

“A weak La Niña would be less likely to result in conventional winter impacts, though predictable signals could still influence the forecast guidance (e.g., CPC’s seasonal outlooks),” CPC said.  

IOD may emerge in Nov

ENSO-neutral continued in October, as evidenced by overall near-average sea surface temperatures (SSTs) observed across the central and eastern equatorial Pacific Ocean. Similar to September, the latest weekly Niño indices ranged from +0.2C (Niño-4) to -0.3C. 

Below-average subsurface temperatures persisted across the east-central and eastern equatorial Pacific Ocean. Collectively, the coupled ocean-atmosphere system reflected ENSO-neutral, it said.

While projecting that La Nina is unlikely to emerge before February 2025, BoM said negative Indian Ocean Dipole (IOD) will likely emerge this month and will continue till December. 

Initially, La Nina was projected to emerge in July this year but meteorological agencies have found that the weather event is yet to emerge. BoM said the sustained nature of significant global ocean heat suggests that climate indicators such as ENSO (El Nino Southern Oscillation) and IOD may not behave or evolve as they have in the past.