Western Australian rainfall outlook

Issued 28 May 2014

A drier winter likely for northwestern and southern Western Australia

Summary

  • A drier than normal winter is more likely for the northwestern and southern parts of WA
  • Climate influences include a warming tropical Pacific, and an easing of the warm eastern Indian Ocean
  • Outlook accuracy is moderate to high over much of western, central and southern WA
Probability of exceeding median rainfall, large image

Details

The chances of receiving above median rainfall for winter are 30 to 40% in the northwestern and southern parts of WA. In other words, the chances of below average rainfall are 60 to 70% in these areas. For every ten winter outlooks with similar odds to these, about six or seven winters would be below average, while only about three or four of them would result in above-average rainfall over these areas.

For the remainder of the State, there is no significant shift in the odds towards either a wetter or drier than normal season.

Climate influences

The El Niño-Southern Oscillation (ENSO) is currently in a state of transition towards El Niño. Dynamical models surveyed by the Bureau indicate that further warming of the tropical Pacific is likely in the coming months, with models approaching or exceeding El Niño thresholds during late winter.

Models indicate the currently warm tropical eastern Indian Ocean is likely to return to near normal. The Indian Ocean Dipole (IOD) is expected to remain neutral for the next three months, and is therefore unlikely to have a significant influence upon this outlook. Positive IOD events often coincide with El Niño and are typically associated with lower than average winter and spring rainfall over parts of southern and central Australia.

How accurate is the outlook?

Outlook accuracy for the winter period is:

  • Moderate to high over much of western, central and southern WA
  • Low over northern and eastern WA