Uncertainty prevails over emergence of La Nina

Uncertainty prevails over the emergence of the La Nina weather with Australia’s Bureau of Meteorology saying El Nino-Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) will remain neutral during the southern hemisphere spring.

“The Bureau’s model indicates a neutral but cooler than average ENSO state. Of the remaining 6 international models surveyed by the Bureau, 3 indicate SSTs (Sea Surface Temperatures) in the central tropical Pacific remaining within historically ENSO-neutral values (between −0.8 °C and +0.8 °C), and 3 indicate SSTs exceeding the La Niña threshold (below −0.8 °C) from October,” said the Australian weather agency said in its latest Climate Driver Update. 

Historically, the ENSO forecast skill is high at this time of year for up to 4 months ahead. This means it is possible a La Niña may develop in coming months. ENSO and IOD are currently neutral, BoM said. 

SSTs neutral

Sea surface temperatures (SSTs) in the central equatorial Pacific Ocean are ENSO-neutral, having gradually cooled from El Niño levels since December 2023. This cooling is being sustained by deep waters surfacing in the central and eastern Pacific. Atmospheric patterns, including cloud and trade winds, remain largely ENSO-neutral, it said.

The IOD is currently neutral, with the latest weekly IOD index value (as of 1 September) of +0.15 °C. Most models indicate that the IOD is likely to remain neutral until at least the end of (Southern hemisphere) spring (September 22-December 22).

With the current global pattern of warmth differing from historical patterns of SSTs associated with ENSO and IOD, future predictions of ENSO and IOD based on SSTs during past events may not be reliable, the agency said.