El Nino/La Nina advisory is issued when the event makes a beginning and is likely to continue. The sea surface temperature in the equatorial Pacific has signs of breaching the threshold mark. The latest projections from NOAA’s Climate Prediction Center show a weak La Nina during winters of the Northern Hemisphere. First things first, these patterns suggested by the models are not guarantees but it does indicate proclivity favouring such trends. What does it mean for climate variability and does it impose any costs? Winter La Nina, as such, has a stronger impact on temperatures but conforming to any typical moisture template remains a grey area. Odds do get tilted in favour of cooler-than-normal conditions.
The Food and Agriculture Organization of the United Nations (FAO) has called for immediate global action to address the impending impacts of La Nina. It follows one of the strongest 2023-24 El Nino climate events on record that affected more than 60 million people worldwide, including severe drought in South Africa. La Nina is not considered kind in all parts of the globe and does impact adversely, the vulnerable sections, like agriculture. Anticipated between Oct-Nov 2024, and expected to persist through Jan-Mar 2025, La Nina will lead to weather extremes with serious consequences for food security, particularly, for those who urgently need assistance.
ENSO: The forecast indicates equal chances for continued ENSO-Neutral conditions in Sep-Nov and a potential transition to La Nina in Oct-Dec 2024. Thereafter, weak La Nina conditions are likely to remain dominant till Jan-Mar 2025. In Feb-Apr 2025, ENSO-Neutral becomes again the most preferred category and remains so for the remainder period of forecast. The probability of return of El Nino lies quite low. However, caution is advised in adopting these forecasts, as the skills of the models degrade at longer leads.
Oceanic and atmospheric conditions across the tropical Pacific favour ENSO-Neutral conditions. However, the Southern Oscillation Index display an inclination to migrate into the La Nina domain, earlier than the oceanic component. The Nino indices in the equatorial Pacific Ocean seem to be unsettled. Nino 3.4, the marker of ONI, for the first time has breached the threshold value of -0.5°C. It remains to be seen whether these conditions will be sustained.
IOD: The Indian Ocean Dipole is currently neutral. For the last three weeks, on the trot, the index is hovering close to zero. The weekly IOD index value as of 22Sep2024 was -0.03°C. Most models indicate that the IOD is likely to remain neutral, but slightly negative during the fall of the year. An IOD event is unlikely.
MJO: Madden-Julian Oscillation pulse was nearly stalled for quite some time over the Western Pacific and Western Hemisphere. The amplitude of the MJO signal kept fluctuating but it has now regained strength. It is likely to resume eastward propagation and enter the Indian Ocean during the first week of October 2024. Climatologically, the Bay of Bengal basin experiences its second mode of tropical cyclone formation, entering October.
The monsoon withdrawal commenced, a little later than the schedule. The retreat of monsoon favours the incremental rise of sea surface temperature. Accordingly, Indian seas become more active basins to host tropical cyclones. The position of MJO over the Indian Ocean will increase the potential of cyclogenesis in the first half of October 2024.