Sometimes, the synoptic weather patterns can have greater influence over periods of a couple of weeks than the climatic indicators on which longer term predictions are based. Usually, the synoptic patterns are used to describe the weather while the longer-term models indicate the climate.
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The synoptic patterns over the past month, and past two weeks especially, have been unusual with strong, nearly stationary high pressure south of Tasmania. It has cradled troughs of low pressure over inland eastern Australia fed by onshore winds picking up moisture from the warm seas to Australia's east.
The unusual warmth of the sea surface temperatures in the western tropical Pacific, the Coral Sea and the Tasman Sea has been the main reason why rainfall in much of eastern and northern Australia has exceeded normal over the past six months or so.
Global SSTs have been the warmest on record for each month between April 2023 and April 2024. This situation appears to be influencing long-term model behaviour. As the current global ocean conditions have never been previously observed, inferences of how the El Nino-Southern Oscillation may develop across the Pacific in 2024 that are based on past events can no longer be made.
That said, most modelling suggests that the ENSO will likely remain neutral until at least early August. This also could mean that the current pattern of occasional rain events for NSW and Queensland could persist in winter, although they will become less frequent. It also means drier than normal weather for Victoria, Tasmania and south east South Australia.
Balancing this prognosis, The Indian Ocean Dipole is likely to stay positive through winter. A positive IOD reduces the potential for north west cloud bands - a pre-frontal phenomenon which brings regular useful rains to all the south east third of the continent. Even the IOD is unusual this year with over 90 per cent of the ocean warmer than normal.
The outlook for spring remains unclear, although the chances of a La Nina returning is the slightly favoured scenario. This would increase the chances of above average spring rains. The alternative is for neutral conditions persisting with on and off rain events keeping overall total to near normal in NSW and Queensland.
With all possible scenarios, it is expected that both maximum and minimum temperatures will remain above average for the rest of the year. However, this expected warmth will not prevent the occasional brief but significant cold spells occurring a couple of times in the winter months. The timing of such events will be critical for the snow season in the Snowy Mountains, but the overall scenario for snow is not great at this stage.
