El Nino and IOD are both going strong, holding their peak values. They do not seem to be scooting soon. Which one blinks first, is anybody’s guess. Historic records vouch for IOD smoothening first, not later than December. ENSO neutral is likely but not earlier than May 2024.
ENSO: Monitoring of ENSO conditions mainly focuses on sea surface temperature (SST) anomalies in four geographical regions of the equatorial Pacific. SST anomalies =/> than 0.5°C in the Nino 3.4 region (170°W-120°W) are indicative of ENSO’s warm phase. Nino 3.4 has an overlapping layer from Nino 3 & Nino 4 regions. It is taken as a principal measure for assessing, monitoring and predicting El Nino. Nino 3.4 anomalies are averaged over the three months ending with the current month and that value is called the Oceanic Nino Index (ONI). When the ONI exhibits a warm phase ( >/= 0.5°C), for at least five consecutive values, it is declared as an El Nino event.
Although the precise reason for ENSO development still remains far from fully understood, the linkages between its two components have been firmly established. The departure in the SST represents El Nino, the atmospheric arm is attributable to the pressure variation between Tahiti and Darwin.
Nino 4 and Nino 3.4 have recorded the highest positive departure since Feb 2016. Following the strong El Nino of 2015, the warming persisted till spring of next year (May 2016). Similar conditions are expected during the current episode as well.
IOD: The positive Indian Ocean Dipole event continues and is maintaining strong levels. The latest weekly value of the index was + 1.49°C for the week ending 19th Nov 2023. The IOD index value for the event has been the 2nd highest since records of the Australian Bureau SST dataset began in 2001, with the highest value occurring in the strongest positive IOD event of 2019. The highest value of IOD during the current episode was +1.92°C on 15 Oct 2023.
MJO: The Madden Julian Oscillation is currently over the Western Hemisphere and Africa in Phase-1. It is likely to move over the Indian Ocean in Phase 2&3. A Substantial increase in amplitude is anticipated as well. The dominance of ENSO and IOD is making the diagnosis of MJO difficult. Notwithstanding, the current scenario augurs well for enhancing the pulse of clouds and rain over the Indian seas, more so over the Bay of Bengal. An uptick in the weather activity is likely during the last days of Nov and rolling over further to the first week of December. Cyclone formation has already been indicated over BoB anytime soon. This may as well be followed by another cyclone spinning up in quick succession.
While El Nino is expected to accentuate the Northeast Monsoon over South Peninsula, active MJO will trigger strong activity over the Indian seas, in the coming days. ENSO neutral during the next southwest monsoon may be construed as a welcome pointer for the economy.