Western Australian rainfall outlook

Issued 25 June 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 warm Indian and Pacific oceans
  • Outlook accuracy is moderate over western and far northern WA
Probability of exceeding median rainfall, large image

Details

The chances of receiving above median rainfall for July to September are about 50% over most of WA. This means odds of above or below median rainfall are about equal in these areas. The chances of receiving median rainfall are less than 40% in the eastern Northern Interior. In other words, the chances of below median rainfall are above 60% in the region. However, it should be noted that northern WA is presently in its 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, the increase in Pacific Ocean temperatures has levelled off in recent weeks. Despite some easing in the model outlooks, international climate models surveyed by the Bureau still indicate El Niño is likely to develop by spring 2014. While POAMA, the model that produces the seasonal outlooks, does not forecast a high probability of El Niño, it retains a drier signal across the country due to patterns in the ocean and atmosphere across the Pacific. This drier signal is consistent between international models regardless of their ENSO forecast.

Models indicate the currently warm Indian Ocean is likely to remain warm. 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.

How accurate is the outlook?

Outlook accuracy for the July to September period is:

  • Moderate over western and far north of WA
  • Low to very low over the rest of WA