Issue Notes

ENSO status: Inactive.
IOD status: Neutral, becoming positive.
SAM status: Neutral, favouring positive in winter.

The El Niño Southern Oscillation (ENSO) is in an inactive phase. 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 firmly neutral after weakening early in the year. A neutral ENSO typically has no significant impact on Australian rainfall during winter.

The Indian Ocean Dipole (IOD) is in a neutral phase. Ocean temperatures are at record levels in the western Indian Ocean, and the IOD index is spiking in response. Persistent southeasterly winds have set in over the eastern Indian Ocean, signalling that the atmosphere is starting to respond to the ocean patterns. A burst of tropical activity expected in mid-May could make-or-break this event, as tropical activity in certain locations could either strengthen or hinder the development of a positive IOD. If this tropical activity is favourable for a positive IOD, significant upwelling near Indonesia may occur as soon as late-May. 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. A positive SAM increases easterly winds, increasing rainfall and thunderstorm activity in the east, while cooling temperatures. A positive SAM reduces cold fronts and rainfall over southern Australia, particularly for southwest WA.

Rainfall outlooks are showing slightly below average rainfall over winter for WA, and the southwest coasts of SA, Vic and Tas. Conversely, above average rainfall is expected for eastern parts of Qld and NSW, and potentially eastern Tas.