La Nina Ends: Final La Nina Advisory Issued
Apr 19, 2025, 3:30 PM | Skymet Weather Team
La Niña Ends With The Beginning of ENSO-neutral phase | Image: Skymet
La Niña, a natural climate pattern that can influence chaotic weather conditions over many parts of the globe, has ended. The La Niña pattern started emerging at the fag end of last year and effectively lasted in Jan and Feb 2025. There were enough indications of its likely collapse in March 2025, and it eventually faded at the start of the spring season. The ENSO Alert System Status by the Climate Prediction Centre (CPC) has now changed and a Final La Niña advisory has been issued. Earlier, the La Niña Advisory remained in vogue from the autumn of last year till March 2025. A La Niña Advisory is issued when La Niña is observed and expected to continue. The final La Niña Advisory is issued when La Niña conditions have ended.
The tropical Pacific had started cooling during Autumn (Northern Hemisphere) of last year, but then the cooler-than-average ocean temperatures in the tropical Pacific Ocean that typically mark the commencement of La Niña, did not reach the threshold until the end of the year. It was the shortest La Niña event since the records began in 1951. The ONI remained -0.5°C or less just for two quarters, Nov-Dec-Jan and Dec-Jan-Feb. The La Niña event this season had the dual distinction of being the weakest and shortest.
ENSO: Now, neither La Niña nor its counterpart El Niño are present and the ENSO-neutral state has begun. This neutral phase is forecast to last through the rest of spring, summer and into at least early fall of 2025. This has happened after more than a decade that just before and after the commencement of the southwest monsoon, the Pacific conditions will remain neutral. Though officially, La Niña has made an early exit, the remnants and fingerprints will linger for a few more weeks or possibly months. Water has a long memory and the sea conditions do not get turned over like any on/off switch. But, it is difficult to qualify as to how long and to what extent the residual effect of La Niña could stick around.
In March 2025, sea surface temperatures in the central and east Pacific were no longer as cool as before. NOAA scientists had confirmed that conditions have shifted back to ENSO-neutral. In the Nino 3.4 region, which tracks the ENSO status, the monthly average anomaly was nearly zero-zero degree Celsius, much warmer than the La Niña threshold of -0.5°C. During first half of April 2025, the SST anomaly is stuck at -0.1°C. This is expected to get warmer during rest of April and upcoming month of May.
IOD: The Indian Ocean Dipole is an inherent mode of climate variability over the Indian Ocean, independent of El Nino/ La Niña phenomenon. In the positive IOD phase, higher than normal SST’s and increased convective activity is seen over western part of tropical Indian Ocean. Such conditions boost the rainfall during Indian Monsoon. The IOD is neutral. The latest value of the IOD index for the week ending 13thApr 2025 was 0.11°C. Neutral IOD values, between +/- 0.4°C are likely in the next 4 weeks. As per BoM, neutral IOD conditions are likely until at least August 2025. However, the skill for IOD forecasts at this time of the year has historically been low for forecasts beyond a month ahead.
MJO: The Madden Julian Oscillation has been inactive since late March. The pulse is likely to meander with in the unit circle for couple of weeks. Cessation of La Niña and return of ENSO-neutral presage tropical forcing. The ensemble model suggests reemergence of MJO across Western Pacific in the last week of April 2025. Suppressed convective activity is expected on either side of the coastline in the Indian Seas. Formation of any tropical cyclone is highly unlikely over Bay of Bengal and Arabian Sea during April 2025.
Neutral ENSO and IOD has left the monsoon to fight its own battle. Though, ENSO-neutral reduces the probability of drought or excess rainfall during monsoon season, but overall, Monsoon is much more difficult to predict under ENSO-neutral conditions. Spring barrier and quick transition from La Niña to ENSO-neutral leave the forecasters in limbo. Predictability drops and uncertainty catches up till the tropical conditions get stabilized.
