La Nina, a cold event that leads to heavy rainfall and floods in Asia particularly India, is expected to emerge by October as the rate and extent of cooling of sea temperatures at the surface and depth have slowed since June, Australia’s Bureau of Meteorology (BoM) has said.
“Compared with earlier forecasts, the potential for La Nina development is now later in (southern hemisphere) spring,” it said in its latest update. The southern hemisphere spring begins around September 22 and lasts till December 22.
BoM said 4 of 7 climate models suggest the possibility of sea surface temperatures (SSTs) reaching the La Nina threshold — which is below −0.8 °C — by October. The remaining three models maintain predict the conditions will be El Nino-Southern Oscillation (ENSO) neutral.
CPC prediction
Over the past couple of weeks, only three of the seven models predicted the emergence of La Nina. Initially, La Nina - known as “Little Girl” in Spanish - was expected to emerge in June but weather agencies across the globe are now predicting it will set in between August and October.
La Nina and El Nino (which brings drought and prolonged dry periods in Asia) are both triggered by the sea surface temperatures in the Pacific Ocean.
Earlier this week, the Climate Prediction Center — a unit of the National Oceanic and Atmospheric Administration (NOAA) of the US — said the ENSO-neutral condition is expected to continue for the next several months.
ENSO-neutral conditions
It said there is a 70 per cent chance of La Niña developing during August-October and a 79 per cent chance of the weather event persisting into the Northern Hemisphere winter 2024-25 that lasts till January 2025.
The APEC Climate Center in its update a week ago said La Nina will emerge between August 2024 and January 2025.
BoM said SSTs, which began cooling in December 2023 in the central Pacific Ocean, are ENSO-neutral. This surface cooling was sustained by deep waters surfacing in the central and eastern Pacific before the slowdown began.
“Atmospheric patterns, including cloud and surface pressure, are currently ENSO-neutral,” the Australian weather agency said, adding that ENSO is likely to remain neutral until at least early spring.
Problems with future predictions
On the other hand, the Indian Ocean Dipole (IOD) is currently neutral. The latest model outlooks indicate that the IOD is likely to remain neutral until at least the end of (southern) winter (August). “Three of 5 climate models suggest that during spring, negative IOD development is likely, while 2 maintain a neutral state of the IOD,” BoM said.
Pointing to global SSTs being the warmest on record for each month between April 2024 and June 2024, the Australian weather agency said the current global pattern of warmth differs to historical patterns of SSTs associated with ENSO and IOD.
“This means future predictions based on SSTs during past ENSO or IOD events may not be reliable. Phenomena such as ENSO and the IOD are only broad indicators of the expected climate,” said BoM.