There is yet no consistent or sustained signal of the La Nina weather pattern, which results in heavy rainfall in Asia and drought in the Americas, emerging, Australia’s Bureau of Meteorology (BoM) said on Tuesday.
This is despite some atmospheric indicators such as pressure, cloud and trade wind patterns over the Pacific being more La Nina-like over the past few weeks, it said in its latest Climate Driver Update.
“The El Nino–Southern Oscillation (ENSO) is neutral, with both sea surface temperatures (SSTs) in the central equatorial Pacific Ocean and atmospheric patterns at ENSO-neutral levels,” said BoM.
Within neutral range
The Bureau’s model suggests that sea surface temperatures (SSTs) will likely remain within the ENSO-neutral range (−0.8 °C to +0.8 °C) throughout its forecast period to February 2025.
Of the 6 other climate models surveyed, 3 suggest SSTs in the tropical Pacific are likely to exceed the La Nina threshold (below −0.8 °C) from October, and another 3 models forecast SSTs to fall just short of the threshold from November, said the Australian weather agency.
“Should a La Nina develop in the coming months, it is forecast to be relatively weak (in terms of the strength of the SST anomaly) and short-lived, with all models indicating a return to neutral by February,” said BoM.
US agency forecast
The Climate Prediction Center (CPC, an arm of the US National Oceanic and Atmospheric Administration (NOAA), said the departure in SSTs (Nino 3.4 index) is currently -0.4ºC, which indicates that the emergence of La Nina is getting delayed.
CPC considers El Nino or La Nina conditions to occur when the monthly Niño3.4 departures in Ocean Index Sea Surface temperatures meet or exceed +/- 0.5ºC along with consistent atmospheric features. These anomalies must also be shown to persist for 3 consecutive months.
The Australian weather agency said the Indian Nina or Indian Ocean Dipole (IOD) is currently neutral, with the weekly IOD index of −0.39 °C (as of 29 September). Most models indicate that the IOD is likely to remain neutral, but weakly negative, for the rest of the year. An IOD event is unlikely.
Sea surface temperatures
Sea surface temperatures (SSTs) for the week ending 29 September 2024 were 0.8–2 °C warmer than the 1991–2020 average across much of the central and eastern Indian Ocean but close to average in parts of the western Indian Ocean.
Some cooler than average waters have expanded near the Horn of Africa in the last fortnight over the western pole of the IOD. Closer to Australia, SSTs were up to 2 °C warmer than average for waters surrounding northern WA, said BoM.
Most climate models indicate the IOD is likely to remain neutral, but weakly negative, for the rest of the year. One model indicated a negative IOD during October and November, the Australian weather agency.