El Nino will be a matter of concern and remain in the run for the next several seasons like Jan-Feb-Mar, Feb-Mar-Apr, Mar-Apr-May and could be Apr-May-Jun as well. The IOD index has tipped below the threshold value of +0.4°C. As the monsoon trough gets established in the Southern Hemisphere, it is likely to drop further and may reach zero-zero in March 2024. The Southern Oscillation Index, the support arm of El Nino has collapsed and changed signs in the transition month of January 2024. It is too early to speculate the role of MJO in the later months when the ITCZ decisively shifts to the Northern Hemisphere. Devolving El Nino, re-emergence of IOD, postulation of MJO and tentative role of Southern Oscillation will make the upcoming southwest monsoon rather interesting but difficult to decode.
ENSO: After the collapse of triple dip La Nina, the El Nino 2023 build-up was brisk and speedy. The eastern equatorial Pacific Ocean warmed explosively, with the Nino index breaching anomaly of +3°C during July & August 2023. It had all the constituents of being simulated as ‘Canonic’ El Nino. However, the characteristics changed phenomenally during the winter months and the change is still continuing. The central Pacific became much warmer than the flank on either side. This feature is synonymous with ‘Modoki’ El Nino. Both types of El Nino have different implications on the climatic conditions and weather hazards around the globe.
All the Nino indices have retained the positive anomaly. Central Pacific remains warmer than either side. Positive sub-surface temperature anomalies have weakened at depth, but persist in the layers closer to the surface ( ~ 100meter depth) across most of the equatorial Pacific. No rapid cooling is anticipated, particularly in the Oceanic Nino Index region of 3.4. However, the continuation of strong El Nino loses support as the SOI has turned significantly positive. A reversal in the sign of this index may be construed as likely weakening of the El Nino component and a step closer to ENSO neutral.
IOD: Indian Ocean Dipole has turned neutral. The index value for the week ending 04 Feb 2024 was 0.3°C. The index has weakened and remains below the threshold of +0.4°C for the second consecutive week. The model forecast indicates the IOD to be neutral until at least April, which is consistent with the annual cycle of IOD. The fresh build-up, starting from scratch of zero-zero may keep it suppressed below the positive threshold of +0.4°C, till well beyond the onset phase of the southwest monsoon.
MJO: The Madden-Julian Oscillation is currently over the Central Pacific and is likely to remain there for the next 2 weeks, albeit with a shortened amplitude. The pulse will have the positional hazard of weakening the trade winds in the central to western Pacific. This will, in turn, temporarily stall the cooling of SST’s and help El Nino to retain its breath a little longer than anticipated. Enhanced convection associated with MJO is expected to trigger tropical cyclone development over the Southern Pacific Ocean. Northern Hemisphere will remain impervious to any El Nino-related enhanced precipitation in the tropics, except the Pacific coast of the U.S. Possibly, the MJO had earlier aided the deep layers of moisture, off the west coast, generating atmospheric rivers, leading to deluge over California.
Remnant effect of El Nino, the marginal existence of IOD and the uncertain role of MJO will make it challenging to read the monsoon footprints of the season. Although, the preliminary estimates do favour a positive outcome. Confirmation still remains a far-fetched conclusion.