The neutral El Nino-Southern Oscillation (ENSO) conditions are now expected to persist for a couple of months, but the setup is far from the usual that we have come to expect in the past. It will be important to watch how the sea surface temperature patterns evolve over winter and early spring.
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The Australian Bureau of Meteorology has a La Nina watch in place for spring, but all this means is that there is about an equal chance of a La Nina and neutral ENSO conditions in the same outlook period.
As is the case when an El Nino breaks down, SSTs in the central Pacific have been steadily cooling in recent months and this cooling has been supported by a significant amount of sub-surface cooling as well, resulting in a quite rapid breakdown in the El Nino. In the past month or two, cloud amounts and the atmospheric pressure patterns are also now neutral, with the 30-day running mean of the Southern Oscillation Index continuing to slowly increase; it is now sitting around +2.
Further cooling in SSTs in the central tropical Pacific is likely to continue over the coming months but major models are almost equally divided in forecasting whether this cooling will cease in late winter, leaving a neutral pattern or whether it will continue into the La Nina "range".
To the west, the Indian Ocean Dipole is neutral with the latest week just below the positive IOD threshold. Predictability of the IOD is low at the moment because most of the Indian Ocean is warmer than normal, and this warmth looks likely to be maintained into winter.
As noted previously there are a few complicating factors. Global SSTs have been the warmest on record for each of the past 14 months. This global pattern is affecting the typical historical patterns of SSTs associated with ENSO and the IOD. As the current global ocean conditions have not been observed before, historical comparisons become unreliable as predictive tools.
In addition, closer to Australia, SSTs were up to 3 degrees warmer than usual off much of Australia's eastern coastline, south of Tasmania and around northern Australia. In the past month, SSTs have increased a little to the south-east of Australia and decreased slightly off the coast of Queensland but are still up on normal overall.
Regardless of any other indicators, these warmer than normal waters increase the potential for rain whenever there are deep onshore wind flows. Such occurrences are rare in the winter months but can provide significant rainfall in short events for parts of the eastern states, but such events can be separated by extended dry spells.
