Western Australian rainfall outlook

Issued 24 July 2014

Equal chance of wetter or drier season likely for most of Western Australia

Summary

  • Equal chance of drier or wetter season for most of WA
  • Climate influences include a brief negative Indian Ocean Dipole, and near-average Pacific waters
  • Outlook accuracy is moderate or better over the Kimberley, Pilbara, Gascoyne, Goldfields and Eucla districts, and in the southwest.
  • Details are summarised in our new monthly Climate and Water Outlook video
Probability of exceeding median rainfall, large image

Details

The chances of receiving above median rainfall for August to October are about 50% over most of WA. This means the odds of above or below rainfall are about equal over most of WA. The chances of receiving above median rainfall in parts of the Northern Interior district lie between 60 and 65%. Northern parts of WA are currently in their dry season, and rainfall at this time of year is far less than is received during the summer months.

Climate influences

Warming of the tropical Pacific Ocean over the past several months has primed the climate system for an El Niño in 2014. However, in the absence of the necessary atmospheric response, Pacific Ocean temperatures have either stabilised, or some cooling has occurred. Despite some further easing in the model outlooks, a majority of international climate models still indicate El Niño is likely to develop during spring 2014. While there are some differences in ENSO outlooks, the near-average to drier-than-average signal across eastern Australia is generally consistent between international models.

The Indian Ocean Dipole (IOD) index has been below −0.4°C (the negative IOD threshold) since mid-June. Model outlooks suggest the IOD is likely to return to neutral by spring. A negative IOD typically brings wetter winter and spring conditions to inland and southern Australia. It is possible that the effects of the Indian Ocean and Pacific are competing to some degree, minimising the likelihood of broader rainfall signals.

How accurate is the outlook?

Outlook accuracy for the August to October period is:

  • Moderate or better over the Kimberley, Pilbara, Gascoyne, Goldfields and Eucla districts, and in the southwest
  • Low to very low over the rest of WA