El Nino Unstoppable: Peak Likely In November

Key Takeaways:

• Nino 3.4 has reached 2.1°C, its highest value of the season, while BoM's Relative Nino 3.4 stands at +2.53°C.
• Forecasts indicate Nino 3.4 could climb above 3°C during October-November 2026 as the El Nino continues to intensify.
• The IOD has remained positive for a second consecutive week, reaching +0.7°C, its highest level since March 2026.
• The MJO is gaining amplitude near the Indian Ocean, but its signal continues to be overshadowed by exceptionally strong El Nino conditions.
• Forecast Validity: Until Next Update.

A super El Nino event is firmly established in the tropical Pacific Ocean and is racing towards historic ‘very strong’ intensity. Both oceanic and atmospheric indices reflect values consistent with a strong El Nino, with further intensification likely during autumn.

As per the Bureau of Meteorology, the latest Relative ONI value for the week ending 20th Sep 2026 was 2.53°C. The Climate Prediction Center updated its weekly index dated 21st Sep at 2.1°C. All models continue to support the Pacific warming to peak sometime during late autumn. Relative Nino 3.4 values are forecast to reach levels above the warmest observed since reliable records began. The majority of models are indicating a sharp increase in the index value above 3.0°C. The stronger the event, the longer it is expected to persist and will therefore go beyond spring 2027. Maybe at the cost of repetition, a strong El Nino signal in the Nino 3.4 region does not necessarily mean a strong climate impact all over. After all, El Nino is not the only factor controlling climate change, and the fact becomes more pertinent when the IOD is showing signs of bouncing back to become positive anytime soon.

ENSO: The presence of a very strong El Nino is quite evident from the weakening/reversal of trade winds in the Western to Central tropical Pacific and the reduced cloud cover over the Maritime Continent. The strong El Nino signal is not allowing the MJO pulse to recuperate and recover from the stifling effect of excessive warming of the Pacific Ocean. The Southern Oscillation Index (SOI), a measure of the atmospheric component of the ENSO, remains strongly negative and far below the El Nino threshold value. It shows persistent and abnormally high air pressure over Darwin (West Pacific) and significantly low pressure over Tahiti (East Pacific). Realistically, the great difference between the two leads to weakening or even reversal of the normal Pacific trade winds that usually blow from east to west.

With respect to the last week, all four Nino indices have warmed up, albeit marginally. Nino 3.4, the marker index of ENSO, has reached its highest value of this season at 2.1°C. As per IRI, a very strong El Nino is intensifying, with Nino 3.4 hitting 3.0°C in October-November and sub-surface heat still surging. The Relative Nino 3.4 index of BoM, placed at +2.53°C, will also cross 3°C around that time.

IOD: After four weeks in the neutral range, the index has turned positive for the second consecutive week. The IOD index value for the week ending 20 Sep 2026 was +0.7°C, the highest since March 2026. Overall, the forecast strongly favours the development and persistence of a positive IOD from Sep to Dec 2026, followed by a transition back towards neutral conditions in early 2027. The emergence of a strongly positive IOD accompanies the exceptional evolution of El Nino, consistent with the documented tendency for these two climate modes to co-occur, while having the feasibility to develop independently as well.

MJO: The Madden-Julian Oscillation will propagate eastward over the Western Hemisphere before retreating westward to the Western Pacific during the first week of October 2026. During the fag end of September, the MJO pulse is gaining amplitude in the proximity of the Indian Ocean in Phase 2. This is significant for triggering convection in the Indian seas. But overall, strong El Nino conditions will dominate the global tropics, and MJO activity remains difficult to discern due to highly anomalous warm waters in the equatorial Pacific.

The active El Nino has suppressed Atlantic hurricanes and tropical storm activity, breaking records for the longest stretch without an Atlantic hurricane in the satellite era as of mid-September, while driving heightened storm activity in the Pacific Ocean.