Pacific forecast indicates continued ENSO-Neutral conditions until Sep-Nov 2024. Thereafter, the forecast shows borderline La Nina conditions emerging during Oct-Dec and Nov-Jan. The probability distribution between La Nina and Neutral remains within the spitting distance from each other. Neutral conditions are expected to return again during winter 2025. It means a weak La Nina may cast a shadow on the Northeast Monsoon and winter rainfall 2024-25. El Nino/ La Nina events change the likelihood of particular climate patterns around the globe, but the outcomes of each event are never exactly the same. While there is generally a relationship between the global impacts of an El Nino/ La Nina event and its intensity, there is always potential for an event to generate serious impacts in some regions, irrespective of its intensity. Mild El Nino conditions during the monsoon months in 2009 inflicted severe drought ( LPA-78%) and a moderate La Nina in the year 2000 could not save the monsoon from a near collapse (LPA-92%).
ENSO: Bureau of Meteorology (BoM) Australia and CPC (NCEP) follow different standards for declaring El Nino/ La Nina conditions. While BoM has a threshold of +/- 0.8°C, CPC criteria suffice anomaly of +/- 0.5°C for the commencement of the El Nino/ La Nina cycle. Since evolving La Nina is likely to be a borderline case this season, the temperature anomaly may not make La Nina a grade for BoM. Whereas, the Climate Prediction Center is quite likely to observe mild La Nina for a brief period of one or two quarters, between Oct 2024 and Jan 2025.
During the last four weeks, near to below-average SSTs persisted in the east-central and eastern Pacific Ocean, while above-average SSTs persisted in the western Pacific. The temperature changes across the equatorial Pacific in the Nino region remained marginal. Nino 3.4 region, the marker for the Oceanic Nino Index (ONI) is just not lifting the cap and getting back to 0.0°C, yet again. At this rate, the drop of an anomaly below the threshold of -0.5°C is unlikely in September 2024. Accordingly, the La Nina profile may not surface till autumn of the Northern Hemisphere.
IOD: The Indian Ocean Dipole remains neutral. The IOD index for the week ending 25 Aug 2024 was +0.16°C. The index has taken a dip from its previous week's value of +0.33°C. The IOD is unlikely to breach the threshold mark of +0.4°C, in the monsoon months. Cooler than normal temperatures in the equatorial Indian Ocean, next to the south Arabian Sea have kept the entire zone stable, throughout the monsoon season, so far.
MJO: The Madden-Julian Oscillation continued to propagate eastward over the Indian Ocean. Its interaction with the equatorial wave has led to the loss of amplitude. However, this weakening will be short-lived and MJO will regain strength while continuing to propagate eastward over the Maritime Continent, during the next two weeks. The model ensemble favours tropical cyclone development over the Western Pacific. The MJO pulse also favours enhanced activity in both, the Arabian Sea and the Bay of Bengal. The augmented phase of MJO will keep pushing the monsoon activity over the Indian seas, at least till mid-September.
There is no implicit support of ENSO and IOD for the southwest monsoon over the Indian subcontinent. Still, the monsoon is sailing comfortably, maintaining class and quality. Monsoon has not entered any ‘break’ so far, even defying the most favoured slot of late August. September is likely to make a promising start and plausibly conclude the season on a satisfactory note.
