El Nino seems to have past its peak. Nino 3.4, representing the Oceanic Nino Index (ONI) has retained the contracted anomaly for the second consecutive week. It is expected to dwindle and commence the march towards neutral ENSO by the close of the spring season of the Northern Hemisphere. IOD has plunged below the positive threshold. Further drop is quite likely, albeit in small slices. The fall of the index may get arrested around the zero-zero mark by early April. SOI is also weakening and may turn absolutely neutral over the coming fortnight.
ENSO: There are only incremental changes in the Nino indices across the central and eastern tropical Pacific Ocean. These changes are on the expected lines and are aligned with the normal process of transition from El Nino to neutral conditions. Ocean waters, as such, have a strong memory and accordingly retain the warmth for fairly long. Oceanic and atmospheric conditions over the tropical Pacific continue to be consistent with the ongoing El Nino event, though, the atmospheric indicators are weakening at a faster pace than estimated. The Southern Oscillation describes a bimodal variation in sea level barometric pressure between observation stations at Tahiti and Darwin (Australia). The weakening of SOI is considered strongly coincidental with the softening of El Nino warmth in the Pacific.
The probabilistic ENSO forecast depicts a somewhat abnormal pattern. The forecast, with strong El Nino at the beginning of the year, collapses by mid-month (May/Jun) and abruptly rises indicating La Nina build-up by the end of the year. A similar pattern was observed in the year 2016, after the cessation of the strong El Nino event of 2015.
IOD: The Indian Ocean Dipole index remained positive since August 2023. The DMI achieved a peak value of 1.92°C during the week ending 15 Oct 2023. The index retained the warmth anomaly of >/= 1°C for nearly four months between Aug 23 and Dec 23. The IOD index has dropped to the season’s low of +0.27°C for the week ending 28 Jan 2024. Crashing of the index below the threshold of +0.4°C typically spells a breakdown of the event. By the way, the event decay has been later than usual, this season. The IOD event, as a routine, builds up between April and November and decays between December and March.
MJO: The Madden-Julian Oscillation has propagated eastward from the Maritime Continent to the Western Pacific in Phases 6 & 7. The enhanced convection elevates the probability of tropical cyclone formation over the Southern Pacific. The tropical oceans over the northern half of the globe do not anticipate any cyclone formation. Tropical disturbances, as such, are the least around this time over these parts. The MJO pulse is likely to move to the Western Hemisphere during the second half of February in Phase 8 with a consistent drop in the amplitude.
Dilution of El Nino conditions to neutral first and immediately building to possible La Nina during the same year will be an interesting feature. A simple corollary, in the Indian context, will be better prospects for the southwest monsoon. But, the Pacific conditions alone can not be considered decisive. Other global parameters impacting the health of the monsoon will have to be factored in, at the appropriate time.