Although the Pacific basin El Nino events and the Indian Ocean Dipole are the dominant influences on our weather patterns in the medium term, there are other climate indicators worth having a look at. For example, to our north there is the Madden-Julian Oscillation. It is currently weak, with a pulse sitting in the western Pacific and this contributed to the development of a category 5 tropical cyclone, Lola, near Vanuatu recently which was the strongest system ever to occur so early in the season in the southern hemisphere.
Interestingly, all years that experienced September or October tropical cyclones in the eastern Coral Sea have been El Nino years (since 1982). Conceptually, this makes sense because in a normal year, the main convergence between the Pacific easterly trade winds and the upper westerly winds occurs across northern Australia while in El Nino years, this occurs further east and is a sign that the main tropical convergence is in fact occurring east of Australia. This is likely to remain a feature until the El Nino weakens.
Traditionally, also, when the MJO pulse is situated in the western Pacific, there is an increased chance of moisture feeding into north east Australia, as has occurred in the past week or two. This has also been assisted by the unexpected continuation of slightly above normal sea surface temperatures in the western Pacific, Coral Sea and Tasman Sea - something that has not occurred before with an El Nino. These features will continue to moderate the effects of the El Nino on potential rainfall in eastern Australia, but they are unlikely to have any effect on the increased temperatures that occur with an El Nino event.
Another climatic indicator, the Southern Annular Mode to the south, continues to provide little guidance. It has been fluctuating between weakly positive and neutral for some time now. At this time of year, neutral SAM is associated with typical climate conditions for Australia. Of all the indicators, the SAM is the most difficult to predict as well.
Longer term outlooks - those in excess of five to six months - remain a little experimental. At the moment, the Pacific El Nino is expected to persist until around May with the likelihood that the majority (but not all) of months between now and then will see rainfall deficiencies through eastern Australia, as well as above average daytime temperatures. By the end of autumn, a neutral pattern becomes the most likely scenario and the effects of the El Nino will weaken further during winter. This means rainfall patterns will return to normal in winter but daytime temperatures are likely to remain above the long-term average due to the influences of global warming.
