12-Month Rainfall Forecast

Issue Notes

ENSO status: La Niña Watch declared. IOD status: Neutral, becoming positive. SAM status: Neutral, favouring positive in winter. The El Niño Southern Oscillation (ENSO) is now in a La Niña Watch, meaning there is approximately a 50% chance of a La Niña developing this year. Ocean cooling is occurring in the eastern Pacific, with 3 out of 7 global models forecasting a La Niña to develop in 2024. Warmer than normal waters are situated in the Coral Sea, providing moisture and humidity to the east coast. The atmosphere continues to be neutral. A La Niña typically increases rainfall over central Australia, Qld and NSW, but has little effect on southern WA, SA, Vic and Tas during winter. The Indian Ocean Dipole (IOD) is in a neutral phase. Ocean temperatures are at record levels in the western Indian Ocean, and upwelling is occurring along the Java Coast in Indonesia. However, the upwelling is mostly occurring outside the IOD East region, and is therefore not reflected in the IOD Index, which is sitting justbelow thresholds. Persistent southeasterly winds have set in, and look to remain strong despite a burst of tropical activity in the region. Models are suggest a tropical low could form in the Bay of Bengal over the coming fortnight, that would help solidify a positive IOD event. A positive IOD reduces the number of northwest cloudbands that cross Australia during winter and spring, reducing rainfall across central and southeastern parts of Australia. The Southern Annular Mode (SAM) is neutral but is expected to favour a positive phase during winter. Furthermore, the long-wave pattern around Antartica is favouring high pressure near Australia for most of June and July, akin to a positive SAM. A positive SAM increases easterly winds across Australia. This leads to increased rainfall and thunderstorm activity in the east, while reducing cold fronts and rainfall over southern Australia, particularly for southwest WA. Rainfall outlooks are showing slightly below average rainfall over winter (mostly June andJuly) for WA, and most of SA, Vic and Tas. Conversely, above average rainfall is expected for eastern parts of Qld and NSW, and potentially eastern Tas. Outlooks turn close to average in August throughout mainland Australia, with Tas still showing drier than normal.