According to the August ENSO outlook, ENSO -Neutral conditions remain across the Pacific, with La Nina favoured to develop during Autumn ( 66% chance), before persisting through the Northern Hemisphere winters ( 74% chance Nov-Jan ). During the last four weeks, there has been no clarity on the behaviour of Nino indices in the central and eastern Pacific. While, both negative and positive SST anomaly changes were observed in the eastern equatorial Pacific Ocean, mostly negative changes were evident in the central and east-central Pacific Ocean. Also, the negative sub-surface temperature anomalies have persisted in the eastern equatorial Pacific Ocean and extended to the surface. Below-average temperatures remain at depth in the central Pacific Ocean. It seems the transition from El Nino to ‘Neutral’ first and then ‘Neutral’ to La Nina remains in an unsettled phase. The La Nina signal is expected to remain weak for the next few weeks.
ENSO: The meteorological and oceanographic data that depict El Nino and La Nina episodes is drawn from various observation platforms. The integration and processing are carried out under programs coordinated by the World Meteorological Organization. The oceanic and atmospheric indicators do not seem to be inclined completely, even for ‘true’ ENSO-Neutral conditions. The Southern Oscillation Index (SOI) has been changing stance, with a large swing from positive to zero, earlier in June 2024 and turning substantially negative again in July. The mismatch between the atmosphere and the ocean has led to the inconsistent state of the ocean.
The uncontrolled fluctuations in the Nino indices in the Pacific Ocean are quite visible. The Nino 3.4 index, the representative of Oceanic Nino Index (ONI) is the marker for monitoring, assessing and predicting ENSO. The index is literally meandering for the last few weeks, beyond any conclusive inference. The index had earlier turned negative, last week, after nearly a gap of 18 months, since March 2023. However, it again reached zero-zero on 12th August 2024. The index necessarily has to drop at or below -0.5°C for the commencement of La Nina conditions. Such anomalies must be forecast to persist for 3 consecutive months before the announcement of the La Nina event.
IOD: The IOD events are frequently observed to co-occur with the El Nino Southern Oscillation (ENSO) conditions in the tropical Pacific. Specifically, positive IOD events are typically accompanied by El Nino and Negative IOD events are commonly linked to La Nina events. ENSO, being a prominent interannual climate variability, can extend its reach to bring about global climate change through atmosphere and oceanic teleconnections. The IOD is currently neutral and reached nearly zero-zero after staying negative for nine weeks. The latest value of the index for the week ending 11th August was +0.05°C. The models project it to become further positive and cross the threshold of 0.4°C in September.
MJO: The Madden-Julian Oscillation is propagating eastward over the Western Hemisphere. Going further, the models have been consistently favouring robust Indian Ocean MJO events that propagate eastward into the Maritime Continent during the next several weeks. With the enhanced phase of MJO gaining amplitude over the Indian Ocean, there are chances of some disturbance coming up, north of the equator, to the east of the Arabian Sea. However, there is a lack of support and the monsoonal shear may not allow it to sustain and grow.
In the absence of any constructive support from La Nina and IOD, the monsoon is driving with its own force. As is normally seen, it is likely to slow down in the second half of August 2024. It may not lead to a typical ‘break monsoon’ as is commonly observed in August, but the spatiotemporal distribution will differ from the first half of August. The northern half of the country is likely to be the main beneficiary during the 3rd week of August.
