The exit of the southwest monsoon and entry of the northeast monsoon has happened simultaneously. Winter monsoon season has commenced on the 15th of October 2024. Northeast Monsoon too, is influenced by global climate parameters such as ENSO, IOD, MJO etc. As per the Bureau of Meteorology (Australia), the chances of La Nina developing in the coming months have decreased, compared to the recent outlooks. Even, if a La Nina were to develop, it is forecast to be relatively weak and short-lived. All models are forecasting neutral values in Feb 2025. But then, BoM standards of SST anomaly are different from the Climate Prediction Center (CPC). And therefore, the existence of La Nina during the fall of the year may become contentious. The CPC forecast firmly suggests the occurrence of La Nina, albeit a decrepit and fleeting event.
ENSO: In line with the strengthening of trade winds over the central-eastern Pacific, the sub-surface cold temperature anomalies have built up over the last few weeks. The IRI ENSO prediction suggests borderline La Nina conditions during Oct-Dec 2024 and they continue during the boreal winters. ENSO-Neutral conditions subsequently reemerge as the most likely category during the Northern Hemispheric spring and remain so till the end of the forecast period.
Nino indices in the equatorial Pacific continue to waver. Nino 3.4, the marker index of La Nina has, once again touched the threshold mark of -0.5°C, the second time in the last four weeks. Its consistency is yet to be established with the subsequent reads. The SSTs, by and large, are conforming to neutral conditions. The atmospheric pattern, coherent with the neutral conditions is yet to be ascertained. Actually, the NCEI data ( National Center for Environmental Information) has suffered some outages caused by Hurricane Helene and the products are yet to be restored. The trade wind pattern does indicate alignment of Southern Oscillation Index with the neutral atmosphere, but yet to be authenticated by the center.
IOD: The Indian Ocean Dipole index has dropped below the negative neutral threshold of -0.4°C. The latest weekly value of the IOD, as of 13 Oct 2024 was -0.58°C. All the models indicate that the IOD is likely to remain neutral, but weakly negative for the rest of the year. The index may often exceed the negative threshold in November, but not for long enough to be considered a negative IOD event. In any case, IOD forecast skills are at the bottom low, at this time of the year and forecasts are unreliable, beyond two months ahead.
MJO: The Madden-Julian Oscillation had a very small amplitude last week and was nearly indiscernible for some time over the Indian Ocean. Now, the MJO pulse is likely to reemerge over the Maritime Continent in the coming days and then move eastward gaining strength and speed before entering the Western Pacific. There is no broad agreement between the models, GEFS, ECMWF, and CFS and this leads to uncertainty on the likely role of MJO in enhancing the convective envelope in the equatorial region. Notwithstanding, the uncertainty in the evolution, as per CPC, the large-scale environment is expected to bring an increased chance of tropical cyclone development over the Indian Ocean and Western Pacific during the next several weeks.
Southwest Monsoon 2024, pulled a decent show, even in the absence of La Nina and positive IOD. La Nina during the Northeast Monsoon does not augur well and occasionally suppresses the seasonal rainfall. Like the summer monsoon, the winter monsoon also is energetic enough to sail through on its own. Much will depend on the frequency and track of the storms in the Bay of Bengal during the season. Strong storms heading for Odisha, West Bengal and Bangladesh lead to a long pause in the monsoon activity over Tamil Nadu and Kerala.