La Nina continues in the Tropical Pacific and has been raging in the largest and deepest ocean of the world, since the time monsoon arrived in June 2020. Ocean and atmospheric indicators reveal a mature La Nina lingering for quite some time without any significant change. Numerical models also suggest that the event has reached its peak at a moderate level and is likely to taper soon to turn neutral during the spring season.
All the 4 Nino Indices in the Central and Eastern Pacific have remained below the threshold value of -0.5°C consistently for the last 3 months. The decisive index of Nino3.4 region crossed the threshold of - 0.5°C in August itself and peaked at -1.7°C in the 1st week of November. La Nina index has peaked for a couple of weeks and now shows signs of decline.
Most numerical models suggest that the current La Nina will persist until Jan 2021. The threshold value of -0.5°C may be breached in March-April. The La Nina pattern has followed a typical seasonal cycle of 12 months with the peak reaching during the fall of year or winter months.
Large parts of the Central Indian Ocean are warmer than the average but IOD (Indian Ocean Dipole) remains neutral. The latest weekly value of the IOD index of 20th Dec stands at +0.1°C. Practically there is no change in this value during the last couple of weeks. IOD values generally oscillate within the normal range during the winter months of December and January. ITCZ (Inter Tropical Convergence Zone), the chief driver of IOD remains over the equatorial region of Indian Ocean and therefore large fluctuations are not observed.
Madden Julian Oscillation (MJO) is relatively weak in amplitude. To start with it is lying over the Maritime Continent, closer to Indonesia and is likely to shift eastward. Its presence there is going to be inconsequential for the Indian Sub- Continent.
La Nina is linked with severe winter over North India and subdued Northeast Monsoon over South Peninsula. Harsh winter is quite evident over the northern parts this season but the phenomenon has a partial verdict for southern states. The winter months of January and February will see the impact of La Nina conditions over North India in the coming days. Northeast Monsoon is going to conclude shortly on a positive note.