The Pacific basin El Nino event has officially ended up quite a bit quicker than originally expected.
Both Oceanic and atmospheric indicators have returned to a neutral pattern. Sea surface temperatures (SSTs) in the central Pacific have been gradually cooling but there has been a substantial cooling over the past two to three weeks.
This surface cooling is supported by a significant cooling in sub-surface waters underneath the central and eastern Pacific, which is typical at the end of the El Nino event. With atmospheric indicators, the Southern Oscillation Index (SOI) is back in the neutral range as well, with a 30-day running mean around -5 - still at the low end of neutral but it is trending more towards the positive. Most long-term international models are supporting neutral conditions for at least a few months, while almost half the major models believe a La Nina pattern will return by around August. It is becoming increasingly likely a La Nina will return in spring, but it is still far from certain.
The sea surface temperatures throughout all oceans on Earth have been the warmest on record for each of the 12 months to March 2024 and it looks as though this trend will continue in April. The global pattern of warmth has not occurred before and therefore climatic predictions involving SST patterns and their developments have a lower level of confidence than usual. This also applies to the Indian Ocean.
The Indian Ocean Dipole (IOD) is currently negative because of unusually warm water in the Indian Ocean but above normal ocean temperatures are also occurring in the NE Indian Ocean south of Indonesia, thus negating the influence of a positive IOD. How this will develop over winter remains unclear as a forecasting tool.
As far as the other climate indicators are concerned at the moment, the Southern Annular Mode (SAM) is fluctuating between neutral and positive as is often the case at this time of year. It is likely to remain neutral for the coming few weeks resulting in minimal rain in Victoria and Tasmania.
Finally, to the north, the Madden-Julian Oscillation (MJO) is weak and little change is expected. It is likely to move away from the Australian tropics anyway and have little or no effect now until spring.
So what this means for rainfall in summary is that over the next six months to late October, there is a 70 per cent chance of above average rainfall in SE and Central eastern Queensland and eastern NSW, a 60pc chance in central and northern inland NSW and at 50pc chance in Victoria, SE South Australia and southern NSW.
