Uncertainty prevails over the strength of a potential drought-bearing weather event, El Nino, though models suggest it could be of at least moderate strength, Australia’s Bureau of Meteorology (BoM) has said. 

This is based on the level of warming in the central tropical Pacific. “A strong El Nino signal in the Niño3.4 region (central tropical Pacific) does not necessarily mean strong impacts…,” it said in its climate drive update on Tuesday.  

All models, including BoM’s, forecast the tropical Pacific to continue warming in the coming months, with sea surface temperatures (SSTs) likely to reach El Nino thresholds by early southern hemisphere winter starting in June. However, for El Nino to be considered established, a corresponding atmospheric response would need to be observed, said BoM.

Warmer-than-average ocean temperatures are expanding over much of the waters surrounding Australia (up to 2°C above average). This is the case in the Tasman Sea, where the forecast points to further warming through winter.

But for El Nino to be considered established, there must be a corresponding atmospheric response, it said. ENSO conditions are neutral, but climate models suggest the trend of warming in the Pacific will persist.

There has been substantial warming in the central tropic Pacific region in recent weeks, with the index warming by about 0.3 °C in the past fortnight and by 1.0 °C since early March. Significant warmth in the sub-surface suggests further warming of SSTs is likely in the coming weeks, the Australian weather organisation said.

The El Nino–Southern Oscillation (ENSO) is currently neutral, although there are signs of possible El Nino development. The latest relative Niño3.4 index value for the week ending 10 May 2026 is +0.52 °C, within the ENSO-neutral range (−0.80 to +0.80 °C). 

Past instances

In the past, El Nino events have led to either late arrival of the South-West monsoon or deficient rain, besides prolonged dry spells. However, before El Nino emerges, India could receive above-normal rainfall.

Atmospheric indicators, including trade winds, pressure and cloud patterns in the tropical Pacific, are consistent with ENSO-neutral conditions.

The Madden-Julian Oscillation is weak, but forecasts indicate it may strengthen again in late May over the Western Pacific and Western Hemisphere regions. If this happens, associated westerly wind anomalies over the western Pacific may further enhance tropical Pacific warming, said BoM.

The 30-day Southern Oscillation Index (SOI) as of 10 May 2026 is −5.9, which indicates a period of more settled weather and above-average pressure over Darwin. The 60 and 90-day SOI values are also showing neutral ENSO values, −5.4 and +3.1, respectively. Sustained values below -7 are indicative of an El Nino state.

The SOI is calculated based on the standardised anomaly of the mean sea level pressure (MSLP) difference between Tahiti (central Pacific) and Darwin (western Pacific).

IoD neutral

The Indian Ocean Dipole (IOD) is neutral at present. The IOD index is -0.04°C as of May 10, 2026. There is a large uncertainty in the forecast state of the IOD.

Most models indicate the IOD is likely to stay neutral at least into early winter (June), with a positive IOD event possible during winter-spring (September). There is a great deal of variation in the model forecasts of the timing and strength of this potential event and the potential outcomes.

The Indian Ocean Dipole is a climate phenomenon that occurs over the Indian Ocean. During a positive phase, warm waters are pushed to the western part of the Indian Ocean while cold deep waters are upwelled to the surface in the eastern Indian Ocean. The pattern reverses during the negative phase of the IOD.

The Southern Annular Mode (SAM) is almost neutral. Over the next two weeks, it is expected to stay largely neutral.

SAM is the dominant climate driver of the Southern Hemisphere, defining the north-south movement of the westerly wind belt that rings Antarctica.

Published on May 12, 2026