Issue Notes

ENSO status: Inactive. El Niño ended.
IOD status: Neutral, becoming positive.
SAM status: Positive, favouring positive.

The El Niño Southern Oscillation (ENSO) has returned to an inactive phase for the first time since August 2021. 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 high across most of the 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. All international models are suggesting the IOD will strengthen into a positive phase over the next 2-3 months, with significant upwelling to start near Indonesia possibly in 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 positive and will favour a positive phase during autumn and into winter. A positive SAM increases easterly winds, increasing rainfall and thunderstorm activity in the east. A positive SAM also reduces cold fronts and rainfall over southern Australia, particularly for southwest WA.

Rainfall outlooks are showing 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.