12-Month Rainfall Forecast

Issue Notes

ENSO status: La Niña Watch. IOD status: Neutral. SAM status: Negative. Trending positive. The El Niño Southern Oscillation (ENSO) is in a La Niña Watch. The current technical definition of a La Niña is only a small chance to be met, although ocean and atmospheric conditions do resemble a La Niña pattern. Trade winds are still stronger than average along the western equatorial Pacific, and Relative-Nino Index (factors in equatorial ocean temperatures elsewhere around the world, compensating for the background warming signal) is below the threshold. A La Niña typically leads to cooler temperatures northern Australia during summer, while producing higher temperatures for western/southwestern WA, Vic and western Tas. The Indian Ocean Dipole (IOD) is in a neutral phase. Recent conditions have been like a negative IOD, but it is too late in the year for this climate driver to develop. Once the monsoon establishes over northern Australia, the IOD has no impact on Australia’s weather. The Southern AnnularMode (SAM) is in a brief negative phase, having switched a positive phase in November. Forecasts predict it will become neural in mid-late December and become positive in January and February. A positive SAM decreases the frequency of cold fronts, with more regular high pressure systems and easterly winds. During summer, this increases rainfall over eastern Australia, and reduces rainfall over southeastern SA, western Vic and western Tas. Rainfall outlooks are showing above average rainfall over large parts of the country during summer, with closer to average conditions for the southwest corner of WA, southern SA and Vic, and central parts of Tas.