Western Australian rainfall outlook

Issued 27 November 2013

Wetter summer likely for northwest Western Australia

Summary

  • A wetter than normal summer is more likely for parts of northwest WA
  • The chances of a wetter or drier than normal summer are roughly equal for the remainder of the State
  • Climate influences include a neutral tropical Pacific, and local sea surface temperature patterns
  • Outlook accuracy is moderate over much of WA
Probability of exceeding median rainfall, large image

Details

The chance of exceeding the median rainfall during summer is greater than 60% over parts of the eastern Pilbara and adjacent northeastern Gascoyne. For every ten summer outlooks with similar odds to these, about six of them would result in above-average rainfall over these areas, while about four would be below average.

The chance of receiving a wetter or drier than normal summer period is roughly equal (i.e., close to 50%) over the remainder of the State.

Climate influences

The tropical Pacific has remained ENSO-neutral since mid-2012. Dynamical models surveyed by the Bureau suggest ENSO-neutral conditions are likely to persist at least for the austral summer. This means there is no strong shift in the odds from the tropical Pacific in this outlook.

With major climate influences likely to remain neutral (and hence have lesser impact upon Australia), secondary influences, such as the pattern of warmer-than-normal sea surface temperatures around the Australian continent are tending to drive the Australian climate.

How accurate is the outlook?

Outlook accuracy is related to how consistently the oceans and broad scale climate affect Australian rainfall. During summer, historical accuracy shows the outlook to be moderately consistent over most of WA. Over parts of the eastern and southern WA, the outlook is weakly consistent.