The Pacific Ocean has continued to warm up across the eastern equatorial region, which is typical of a developing El Nino situation. Cool water persists in the north east Pacific off the North American coastline, which is unusual in an El Nino, but elsewhere much of the eastern Pacific Ocean is well above average. The warm water off the South American coastline is likely to spread westwards across the surface further in the coming months.
Also unusual for a developing El Nino, the western Pacific (Coral Sea, Tasman Sea) remains mostly warmer than normal, which adds uncertainty into any normal El Nino prediction. Regardless of whether this persists or not, the very warm water in the eastern Pacific should be more than sufficient to push the Pacific Ocean into an official El Nino as early as June. This is reinforced by a large area of warm sub-surface water in the tropical Pacific near the International Date Line. This should upwell in the coming weeks and months, helping to maintain the warm water anomalies and the El Nino pattern. So, by winter the impacts of the El Nino should become more apparent.
In addition, it is increasingly likely that the Indian Ocean Dipole will become positive. It appears that tropical cyclone Ilsa caused upwelling of cool water and produced a broad region of cool water anomalies here which is artificially inflating the positive IOD signal, but it may also act as a catalyst to push the Indian Ocean more quickly into a positive IOD phase. This will decrease moisture availability feeding into Australia and lower the chance of northwest cloud bands occurring during the winter-spring period.
Considering the developing situation in both the Pacific and Indian oceans, it seems likely that below average rainfall is going to be a feature of the weather in south east Australia for not only winter, but much of spring as well because the developing patterns are approaching those that existed in 2019.
Last spring (2022) was made wetter by a sudden stratospheric cooling event due to the Tongan volcanic eruption and this adds an element of confusion to the long-range forecast with an unknown influence of whether this may continue to have an impact on climatic conditions into 2023.
Overall, however, drier conditions are still favoured, and these tend to result in colder minimums but warmer maximums through the winter period, with an earlier and hotter start to spring/summer. An increase in winter westerlies is likely to see an increase in showers in southern Victoria in the coming one to two months. However, such an assessment has a degree of speculation attached as long term models are often less reliable at this time of year.
