ENSO Turns Neutral: Conditions Favoured Through The Indian Monsoon

After a short stint of La Niña, the tropical Pacific is now ENSO-neutral. These conditions are likely to continue through the Northern Hemisphere summer and may even extend till the fall of the year. ‘ENSO-Neutral' means that neither El Niño nor La Niña are in effect and global seasonal conditions are less predictable. Neutral also means that there is little to no forcing in the Tropical-Pacific. The atmospheric flow is not pushed around in a consistent way and therefore, predictable signals are weaker. Lack of forcing from ENSO pushes the prediction skills of the forecasters to the test. This offers an opportunity to the meteorologists to “look out of the window” to comprehend long-term trends in temperature and changes in the land surface and incorporate them in the seasonal forecasts.

ENSO: While there is generally a relationship between the global impacts of an El Niño/ La Niña event and its intensity, there are hardly any verified inputs available with respect to the ENSO neutral conditions. In the context of the Indian Summer Monsoon, ENSO neutral in 2003 ushered seasonal rainfall of 102% of the Long Period Average (LPA). At the same time, similar neutral conditions in 2012 smashed below normal monsoon at 93% of LPA and akin Pacific conditions in 2013 brought bountiful rains to the tune of 106% of LPA. It may be construed that variability becomes quite large during ENSO-neutral.

The SST anomaly in the Niño 3.4 region during Jan-Mar 2025 was -0.4°C as against the quarterly value of -0.56°C during Dec-Feb 2025. The most recent value in April 2025 has oscillated between -0.1°C and -0.2°C. The IRI ENSO plume forecast indicate a high probability (91%) for ENSO-Neutral conditions for Apr-Jun 2025 and these conditions are favoured to continue through Aug-Oct 2025 with a probability of more than 50%. For the later forecast seasons, Oct-Dec 2025 and Nov-Jan 2026, there is no strong preference for any category, although La Niña share keeps increasing at the cost of neutral till fall of the year.

IOD: The Indian Ocean Dipole is a climate pattern affecting the Indian Ocean. IOD and ENSO together control the monsoon rainfall over Indian Sub-Continent. IOD gains more importance this season as ENSO-Neutral is likely to prevail through the Indian Summer Monsoon. The positive phase of the IOD pushes warm water to the western parts of the Indian Ocean, enhancing monsoon rainfall over India. The IOD is neutral. The latest value of the IOD index for the week ending 20thApr 2025 was 0.07°C. Range of international models are predicting neutral IOD for at least next two months. Skill for IOD forecasts at this time of the year has historically been low for forecasts beyond a month ahead.

MJO: The Madden-Julian Oscillation is characterized by an eastward progression of large regions of both, enhanced and suppressed tropical rainfall observed mainly over the Indian and Pacific Ocean. The pattern of tropical rainfall generally becomes non-descript as the pulse moves over the primarily cooler ocean surface waters of the Eastern Pacific. The wet phase of the enhanced convection and precipitation is followed by a dry phase with suppressed thunderstorm activity. Each cycle lasts approximately 30-60 days. Accordingly, the MJO is also known as 30-60 days intra-seasonal oscillation.

The MJO pulse is propagating over the Western Pacific with slightly increased amplitude. It may enter the Indian Ocean during first week of May, but with smaller amplitude. It may not support any deep convection over the Indian Seas in the next two weeks or so.

None of the oceanic parameters ( ENSO, IOD, MJO ) are in active phase for the next about two weeks. There is least possibility of any storm over the Northern Hemisphere during this period.