Western Australian rainfall outlook

Issued 26 March 2014

Wetter season more likely for western and southern WA

Summary

  • A wetter than normal season is more likely for western and southern WA, whilst a drier than normal season is likely in parts of the Kimberley.
  • Climate influences include a warming tropical Pacific, and a warm to near-normal Indian Ocean
  • Outlook accuracy is moderate to high over most of eastern and northern WA, whilst outlook accuracy is low to very low in parts of western and central WA.
Probability of exceeding median rainfall, large image

Details

The chances of exceeding the median rainfall are 60 to 70% over western and southern WA. For every ten autumn outlooks with similar odds to these, about six to seven of them would result in above-average rainfall over these areas, while about three to four would be below average.

Conversely, the chances of exceeding the median rainfall during April to June are 35 to 40% in parts of the Kimberley. In other words, the chances of below average rainfall are 60 to 65% over this region.

Climate influences

The El Niño-Southern Oscillation (ENSO) currently remains neutral, but the tropical Pacific is currently warming. Dynamical models surveyed by the Bureau indicate that further warming of the tropical Pacific is likely in the coming months, with most models approaching or exceeding El Niño thresholds during the southern winter.

Sea surface temperatures around Western Australia, are expected to be near normal to warmer than normal in the April to June period. These conditions may lead to increased evaporation and atmospheric moisture, and thus potentially explain the wetter than normal outlook for parts of the west.

The Indian Ocean Dipole (IOD) influence is minimal during the first part of the outlook period, with a neutral IOD likely for the second part.

How accurate is the outlook?

Outlook accuracy for the autumn period is:

  • Moderate to high over eastern and northern WA
  • Low to very low over parts of western and central WA