La Nina Tumble Looms Large, ENSO-Neutral Anytime Soon

ENSO is considered one of the dominant modes of climate variability worldwide. Its effect, of course, has to be read in conjunction with other oceanic parameters like IOD, MJO, and the Southern Annular Mode (SAM). Big swipes over developing La Niña are flattening, and the collapse seems untenable, well before the timelines envisaged earlier. ENSO-Neutral is favored to develop in the next month and persist through Northern Hemisphere summer. This shift is mooted by sea surface temperature in the Niño 3.4 region, which is now closer to average, with anomalies falling well below the threshold mark of -0.5°C throughout the Niño region. What does it mean for the ongoing pre-monsoon spring and the upcoming Indian summer monsoon? Big fortunes are at stake for the agriculture sector. Is it going to be an outright farmer’s delight or an anxious wait for any whimsical outcome?

ENSO: As of mid-March 2025, the equatorial Pacific is transitioning from a weak La Niña to an ENSO-neutral state. Surely, it is not a smooth transition, as the La Niña conditions remained poor for a brief period too. In such cases, any quick changeover is resisted by the long haul of cool temperatures over the equatorial Pacific. The Pacific had started cooling with the recession of El Niño in early spring of last year, but the degree of coolness remained subdued and got extended till the fall of the year. La Niña was barely visible at the fag end of last year.

The equatorial Pacific water has been getting warmer and the Nino indices are steadily rising. However, last week's readings have wavered once again, and all the indices have shown a marginal degree of cooling across the board. Nino 3.4, the marker index for ONI, slumped from 0.3°C to -0.1°C on 24th March 2025. It seems difficult for the fall in temperature to be sustained, but it has arrested the regular decline for the last six weeks. Even with this drop in anomaly, the average Nino 3.4 index for the last six weeks works out to be -0.1°C, far below the threshold mark. For ONI of quarter Jan-Feb-Mar to reach a threshold value of -0.5°C, the Nino 3.4 index needs to register an anomaly of -1.1°C or more. It looks improbable, and the quarterly index may not hold the desired mark of -0.5°C. The likely value of this quarter is assessed to be around -0.4°C. If so, this will mark the end of the La Niña episode, or at least ‘break’ the continuity of La Niña this season.

IOD: The Indian Ocean Dipole is a climate pattern affecting the Indian Ocean. It can adversely or favorably interact with the developing conditions in the Pacific Ocean. The warm phase of the IOD raises sea level in the Western Indian Ocean, favoring positive interaction with La Niña and ENSO-Neutral. It raises the prospects of seasonal rainfall during the Indian Summer Monsoon. The IOD is neutral. The latest value of the index for the week ending 23rd March 2025 was 0.45°C, slightly above the threshold mark of neutral. It is rather early to preempt the role of IOD during Indian monsoon.  However, the precursors do not seem to have any adverse effect and the index may support healthy monsoon.

MJO: After having a slow pace of propagation over the Indian Ocean, the Madden-Julian Oscillation is likely to become centric over the Western Pacific for the next two weeks. Though the amplitude has weakened, it is still good enough to sustain deep convection over the region. It may not have the potential to raise a storm over the Western Pacific, but enhanced rainfall activity is quite likely in the ‘Pacific Rim’ countries, more so during the fag end of March and the start of April, before it recedes far to the east over the Central Pacific. Tropical storm activity will remain confined to the Southern Hemisphere during the next two weeks.

ENSO is likely to enter its decisive phase. A lot is hinged on the likely stance it takes, with enduring timelines.  Spring barrier remains a hurdle for precise and accurate predictions, at least for the next four weeks.