Oleochem Analytics — Strengthening model outlooks and recent cooling in the tropical Pacific Ocean has raised the chance of La Niña forming in the fourth quarter of 2021, the Australian Bureau of Meteorology (BOM) said in its latest Climate Driver Update issued September 14.
Australia’s BOM has lifted its El Niño–Southern Oscillation (ENSO) outlook status to La Niña WATCH, meaning around a 50% chance of La Niña forming. This is approximately double the normal likelihood, the BOM informed.
La Niña events increase the chances of above-average rainfall for South East Asia (SEA) and northern and eastern Australia during spring and summer, according to the BOM.
Also, according to the US National Oceanic and Atmospheric Administration (NOAA), during a La Niña year, winter temperatures are warmer than normal in the southern US and cooler than normal in the North area of the US. La Niña can also lead to a more severe hurricane season.
Although most oceanic and atmospheric indicators of ENSO remain within the ENSO-neutral range, sea surface temperatures in the central tropical Pacific Ocean have cooled over the past two months, supported by cooler than average waters beneath the surface, the BOM said.
Five of the seven surveyed models anticipate La Niña thresholds will be met or surpassed for some or all of the months from October to January.
Most surveyed models indicate central Pacific sea surface temperatures (NINO3.4) are likely to cool over the coming months, with three of the seven models suggesting the cooling will be sufficient, and sustained for long enough, to meet minimum La Niña event criteria.
Two additional models briefly touch on La Niña thresholds during the outlook period, with the remaining two models predicting a neutral ENSO to persist through to early 2022, the BOM said.
El Niño and La Niña can both have global impacts on weather and wildfires, among others. Episodes of El Niño and La Niña typically last nine to 12 months, but can sometimes last for years, according to NOAA.