El Nino Triggers September As Second Hottest Globally

Key Takeaways:

• El Niño intensifies: The Niño 3.4 temperature anomaly has reportedly reached +3.4°C, exceeding previous strong-event benchmarks.
• Global temperatures surge: September 2026 was reported as the second-warmest September, with temperatures 1.63°C above pre-industrial levels.
• Positive IOD possible: The Indian Ocean Dipole index reached +0.88°C on 11 October, indicating strengthening positive conditions.
• Northeast Monsoon outlook: A developing positive IOD could enhance rainfall over southern India during the second half of October.
• Forecast Validity: Till Next Update.

Strengthening El Niño conditions have pushed sea surface temperatures (SSTs) to record highs. Even the sub-surface temperatures have crossed the earlier benchmarks of very strong El Niño years. Exceptionally high sea surface temperatures have persisted over much of the tropical Pacific, where El Niño conditions are strengthening to set a new benchmark. The weekly temperature anomaly in the Niño 3.4 region has exceeded previous levels. The mean ocean surface temperature in September over the Niño region, a marker for monitoring, assessing and predicting El Niño, had reached 29.7°C. This is an unprecedented temperature anomaly, which overtakes the previous highs during the very strong El Niño years of 1982–83, 1991–92 and 2015–16.

September 2026 was the second-warmest September ever recorded, as the Pacific Ocean continued to heat up under a strengthening El Niño. As per records at ECMWF, global temperatures in September were 1.63°C above pre-industrial levels, and it was the second consecutive month in 2026 to cross the 1.5°C mark, following August. August was the joint-hottest month ever recorded globally, along with July 2023, with temperatures 1.65°C above pre-industrial levels. It is feared that El Niño-associated warming, coupled with human-induced climate change, may trigger frequent breaches of 1.5°C, and this may continue into 2027.

ENSO: Weather experts from across the world are warning about the speedy intensification of El Niño, reaching unprecedented territory. It is feared that a large area of planet Earth will experience unusually warm conditions as the Pacific Ocean releases enormous amounts of trapped heat. El Niño is near record levels. Both oceanic and atmospheric conditions are aligned and reflect values consistent with a strong El Niño, with further intensification during the fall of the year.

This year's El Niño continues its wrath, heating surface and sub-surface waters to levels unrivalled during previous very strong El Niño events. The Niño 3.4 region anomaly has touched 3.4°C above normal, higher than any prior El Niño event on record. In its forecast, WMO has stated that there is an overwhelming likelihood of above-average sea surface temperatures across large parts of the globe during the final months of 2026. The SSTs in the central and eastern tropical Pacific, the region at the heart of the El Niño phenomenon, were expected to reach a record 3.7°C above normal during the October–December 2026 quarter.

IOD: The Indian Ocean Dipole is currently neutral, although the weekly index value as of 11 October 2026 was +0.88°C. This is the fifth consecutive week that the index has exceeded the positive threshold (+0.4°C). A similar trend over the next 3–4 weeks will qualify as a positive IOD event.

MJO: El Niño continues to overshadow any coherent MJO activity over the global tropics. There has been little shift in the background state in response to the emerging positive IOD in the Indian Ocean. Dynamical models continue to favour an MJO signal reaching the Indian Ocean. The amplitude of the MJO is likely to increase as it propagates from the African phase to the Indian Ocean in Phase 2. However, favourable conditions for cyclogenesis will remain confined to the western and eastern Pacific Ocean. The Indian seas will have to wait for their maiden cyclone of the post-monsoon season.

The Northeast Monsoon has set in, albeit under the growing shadow of El Niño conditions in the Pacific. A likely positive IOD is a good sign for the enhancement of monsoon rains over the southern peninsula. The large deficit across the southern peninsula during the Southwest Monsoon may be partially covered during the second half of October.