El Niño or La Niña? Anomalous temperature pattern keeps confusion alive Premium

India awaits monsoon forecast with anxiety, pondering El Niño or La Niña impact on 2025-2026 weather patterns.

It’s that time of the year again. India waits eagerly for the summer monsoon forecast, tinged with some anxiety about whether it will be ‘normal’. The fate of the monsoon also raises the question of whether 2025-2026 will be an El Niño year or a La Niña year. Even though only 60% of deficit and surplus years have historically been accounted for by El Niño and La Niña events, respectively, they have been perceived as the harbingers of bad news or good news about the monsoons.

There have been many headlines over the last few months claiming the world is in the grip of a La Niña. Is this true? Sea surface temperature (SST) patterns in the tropical Pacific Ocean have evolved in a rather unexpected way since early 2024.

Recall that the El Niño forecasts issued in early 2023 turned out to be quite accurate even as the 2023 summer monsoon was essentially ‘normal’ in terms of total seasonal rainfall.

Recall also that a normal monsoon hardly means an even distribution in space or time. Heavy spells were reported across many States even as parts of Karnataka, Kerala, Uttar Pradesh, West Bengal, and the Northeast registered shortfalls.

The forecasts at the beginning of 2024 seemed equally confident about a strong La Niña for the latter half of 2024. They appeared to validate the presence of cold SST anomalies appearing early in the far eastern tropical Pacific Ocean, which is an expected early symptom of La Niña. Strangely, however, the cold SST anomalies began shifting westward, towards the international dateline, with warm SST anomalies appearing in the far east by early summer 2024.

Anomalies in wind patterns were equally strange: strong easterly anomalies blew in the central-western tropical Pacific even as there were westerly anomalies in the far eastern tropical Pacific.

The unusual pattern of cold SST anomalies to the west of warm SST anomalies in the far east have persisted to date. In the last few decades, the reverse pattern — with warm SST anomalies around the dateline and cold SST anomalies around the Galapagos — has been more common. This pattern has been called the Dateline El Niño or a Central Pacific El Niño.