Equatorial sea surface temperatures (SST’s) are near to above average across most of the Pacific Ocean. After the collapse of ‘Triple Dip La Nina’, negative SST anomalies weakened across most of the equatorial Pacific Ocean starting December 2022. Beginning in January 2023, positive SST anomalies strengthened in the eastern equatorial Pacific. Since early April2023, above average SST’s have persisted across most of the tropical Pacific Ocean.
ENSO : El Nino ‘watch’ was issued in April 2023, indicating start of the warm phase of ENSO. All the Nino indices have remained +ve neutral or above the threshold, since then. The western half of the equatorial Pacific Ocean hosting Nino indices continue to be a borderline case whereas the eastern portion is consistently showing adequate warming.
El Nino is characterized by a +ve ONI (Oceanic Nino Index) >/= 0.5°C. The ONI is in turn based on SST departure from average in the Nino 3.4 region. This also is the principal measure for monitoring, assessing and predicting ENSO. Nino 3.4 has observed marginal changes during May 2023.
IOD: The Indian Ocean Dipole is currently neutral. The IOD index value for the week ending 28 May 2023 was + 0.26°C. The index has turned positive neutral after staying in the negative neutral regime for 3 weeks. Climate models suggest a +ve IOD event may develop in the coming weeks. However, the model predictions are not commensurate with the existing track of IOD. A strong +ve IOD has the potential to dilute the typical drying effect of El Nino over the Indian sub-continent.
MJO: The Madden Julian Oscillation had been quite active over Western Pacific despite super typhoon Mawar navigating through the Philippines Sea. MJO is now in phase-8 and heading for phase 1&2 in the 1st week of June and later getting positioned over the Indian Ocean in the 2nd week of June. The potential for cyclogenesis finds favour over the Indian seas, both Bay of Bengal and the Arabian Sea. There is some disagreement amongst climate models, with some indicating marginal strengthening and continued eastward propagation while others suggest the MJO phase to weaken rapidly and become indiscernible. If the MJO pulse maintains strength and track across central Pacific, it may weaken the trade winds over equatorial Pacific Ocean. This, in turn, would escalate warming of the equatorial Pacific Ocean and speed up El Nino build up.
Indian seas are likely to be active basins during the 2nd week of June. The trio of El Nino, IOD and MJO has a significant role in accelerating the monsoon stream during the initial onset phase. While the forecast tools favour cyclone formation in the Indian Seas, the discrepancy in the timings remains a contentious issue.