CPC Changes ENSO Status: Final La Nina Advisory To ENSO Not Active

The ENSO affects interannual variability throughout the tropics. Analysis of observational data over a long period finds a significant correlation between ENSO and Indian Summer Monsoon Rainfall (ISMR). However, the recent studies have revealed that the relationship between ENSO and ISMR is becoming subtle. Human-induced climate change is overwhelmingly altering the governing characteristics, and therefore, a future weakening of the ENSO-Monsoon relationship could occur in the ensuing warmer climate.

ENSO: The Climate Prediction Center (CPC), the forecasting wing of NOAA (National Oceanic and Atmospheric Administration) has revised the ENSO Alert System Status from Final La Nina Advisory to ENSO-Not Active. It means that ENSO neutral is likely for the next few months. As of mid-May 2025, the equatorial Pacific is in an ENSO-neutral state. The IRI ( International Research Institute) ENSO plume forecast indicates a high probability (92%) of ENSO neutral conditions for May to July 2025. These conditions are expected to continue through Aug-Sep with the probability remaining above 50%. ENSO – Neutral remains the most likely outcome even through the fall of the year, albeit with reduced probability of 40%.

IOD: The Indian Ocean Dipole is neutral. The latest value of the IOD index for the week ending 18th Mar 2025 was 0.24°C. The IOD has dropped back to the neutral range after staying close to the positive threshold of +0.4°C for three consecutive weeks. The BoM model predicts a neutral state of the IOD until at least July, after which it forecasts a shift towards negative IOD. This is aligned with the assessment of other international models, which show an inclination to develop negative IOD at some point between June and September. Exercise caution; the skill for IOD forecasts made at this time of the year has been historically low beyond 1-2 months ahead.

MJO: The Madden-Julian Oscillation continues to be weak. It is likely to meander over the Maritime continent in Phase 5, with subdued amplitude. MJO has remained incoherent all through the month of May so far. There could be a slight uptick in the magnitude, but only for a brief period.

Without any support from ENSO, IOD, and MJO, the Indian seas have been the active basins. A pertinent weather system came up in the Arabian Sea, off the Konkan Coast. Another significant monsoon system is likely to form over the Bay of Bengal shortly. The ill effects of the Arabian Sea systems, normally observed during the onset phase of the monsoon, will quickly get overcome. The possible depression over the Western Bay of Bengal will invigorate the monsoon current and facilitate speedy advancement for the next few days.