Beginning in mid-May 2020, -ve Sea Surface Temperature (SST) anomalies emerged in the east-central and eastern Pacific Ocean. Cooling in the Pacific Ocean strengthened and the La Nina monitoring index (Nino3.4) sustained a long and large -ve phase with anomalies of the order of -1°C to -1.5°C between 27th July 2020 and 08th March 2021. The highest value was -1.7°C in the 1st week of Nov 2020. In the last 2 weeks, -ve anomalies have weakened across the equatorial Pacific Ocean. Nino3.4 index has risen above the threshold value of -0.5°C for the first time since 27th July 2020.
Nino1+2 and Nino3 have turned +ve together for the first time since 11th May 2020. La Nina projection of early March indicates softening during the spring season and a gradual but marginal rise during the monsoon months from July to September.
El Nino factor is the least and the neutral component dominates. La Nina advisory continues as the equatorial SSTs are below the average from the west-central to the eastern Pacific Ocean. There is a ~ 60% chance of a transition from La Nina to ENSO neutral during the Northern Hemisphere Spring 2021 (Apr-Jun).
Closer home, the Indian Ocean is warmer, albeit lightly and the latest value of Indian Ocean Dipole (IOD) has become narrowly +ve at 0.05°C from the earlier mark of -0.15°C on Feb 21. Numerical models suggest the IOD remain marginally +ve till Apr 21 and decline thereafter.
Long term outlook indicates a potential for -ve IOD to develop by Jul 21. Though it is not likely be a strong event threshold of -0.4°C may be breached.
