ENSO-Neutral Strengthen Over Pacific Ocean: Conditions Favoured Through The Monsoon

ENSO is a climatic phenomenon that keeps cropping up due to variations in winds and sea surface temperature over the tropical Pacific Ocean. These variations have an irregular pattern but do have some semblance of cycles. El Niño and La Niña both generally last for a year or so and typically occur every 2-7 years with varying intensity.

Of course, there are exceptions of El Niño lasting for over 18 months (1957-59, 1986-88, 2014-16) and occurrences of triple-dip La Niña (1954-56, 1973-76, 2020-22). ENSO-neutral remains the least known phenomenon for its consequences on global weather. A key mechanism of ENSO is the Bjerknes feedback, in which the atmospheric changes alter the SSTs that in turn modify the atmospheric winds. The exact mechanism that causes the oscillation remains unclear. The Pacific event occurring so frequently still leaves many unanswered questions:

What starts El Niño or La Niña?

How and why does it terminate?

Can we actually predict natural disasters in association with El Niño/La Niña?

Do we have the ability to predict the scale of climate change on account of these events and build the capability to read the collapse or growth of El Niño/La Niña midway?

ENSO: The ENSO is Earth’s main source of year-to-year climate variability. Future trends in ENSO due to climate change are uncertain. But, in the long run, it is quite likely that the precipitation variance related to ENSO will increase.

Equatorial sea surface temperatures are near average across most of the Pacific Ocean. ENSO-Neutral is likely to become sturdier and is favored for the entire monsoon season. The Nino 3.4 index, the marker for ONI and ENSO, is nearly zero-zero for the last three weeks. The latest value of the index as of 12th May 2025 was +0.1°C. The mean value of the index for the last eight weeks was -0.04°C. Both the dynamical and statistical models are indicating an average value of +/- 0.2°C till fall of the year.

IOD: The Indian Ocean Dipole is neutral. The latest value of the IOD index for the week ending 11th May 2025 was +0.39°C. The index , after staying above the positive threshold  of +0.4°C , has come down to the borderline of ‘neutral.’ Most models are predicting the IOD to remain neutral for at least the next two months.

MJO: The Madden-Julian Oscillation is likely to meander within the unit circle with one of the lowest amplitudes. Models are largely unsupportive of coherent MJO reemerging later in May. ENSO-Neutral and weak MJO may not give any push to the monsoon current. However, small-scale circulations over the Bay of Bengal and the Arabian Sea may speed up the cross-equatorial flow and monsoon stream. 

The scientific consensus is that 'it is very likely that rainfall variability-related change in the strength and spatial extent of ENSO telecommunication will lead to significant change at a regional scale'.  Without any external push, the monsoon has made an early time entry over the South Andaman Sea. Conditions are favorable to cover more parts of the Bay of Bengal, Sri Lanka, Comorin, and the Maldives region before the scheduled date.  Kerala is likely to see the earliest onset of monsoon since 2009.