The Australian Bureau of Meteorology (BoM) is predicting that neutral El Nino-Southern Oscillation (ENSO) conditions will continue till the end of the spring in the southern hemisphere (September 22-December 23).
This virtually rules out the La Nina weather event, which results in Asia getting heavy rain and floods, emerging during the southern spring.
Though sea surface temperatures (SSTs) in the central equatorial Pacific Ocean gradually cooled from December 2023 to signal the end of El Nino in April, the extent and magnitude of the water cooling has decreased since last fortnight delaying the onset of La Nina. The rise in SSTs in the central equatorial Pacific Ocean leads to El Nino and the fall to La Nina.
Climate models split
“Atmospheric patterns, including cloud and trade winds, are currently ENSO-neutral,” said BoM in its latest Climate Driver Update.
The Australian weather agency said 3 of 7 climate models suggest the possibility of SSTs in the tropical Pacific exceeding the La Niña threshold (below −0.8 °C) from October, with a fourth just briefly reaching the threshold. “The remaining 3 models suggest SSTs are likely to remain at ENSO-neutral values (between −0.8 °C to +0.8 °C ) throughout the forecast period (September-December),” it said.
A fortnight ago, BoM said three of 7 climate models suggested the possibility of SSTs reaching the La Niña threshold (below −0.8 °C) by October. The remaining 4 models predicted a continuation of ENSO-neutral throughout the forecast period.
Rate of cooling down
It also said the rate and extent of cooling both at and below the surface has decreased since May.
However, the ENSO outlook remains at La Niña Watch. “La Niña Watch does not guarantee La Niña development, only that there is about an equal chance of ENSO remaining neutral or La Niña developing during the remainder of 2024,” said BoM.
For India, the projection means there will unlikely be unseasonal rains that could endanger kharif crops, while weather conditions could be favourable for the sowing of rabi crops.
In 2022 and early 2023, the La Nina weather event resulted in the country receiving unseasonal rains that affected foodgrain and horticulture crops, leading to supply shortages and inflation.
IOD neutral
On the other hand, the Indian Ocean Dipole (IOD) is currently neutral. BoM said the east Indian Ocean has cooled in recent weeks, with the latest weekly IOD index value (as of August 18) at +0.33 °C. However, most models indicate that the IOD is likely to remain neutral until at least the end of spring, it said.
The Australian weather agency said the current global pattern of warmth differs from historical patterns of SSTs associated with ENSO and IOD. This means future predictions of ENSO and IOD based on SSTs during past events may not be reliable.
“Phenomena such as ENSO and the IOD are only broad indicators of the expected climate… Most climate models indicate the IOD is likely to remain neutral throughout spring,” it said.
BoM said SSTs for the week ending August 18 were 0.8 to 2 °C warmer than the 1991–2020 average across much of the Indian Ocean, but close to the average in the far western and eastern equatorial Indian Ocean.