National rainfall outlook

Issued 27 November 2013

Drier summer more likely for parts of northeast Australia

Text commentary of chance of increased rainfall

Summary

  • A drier than normal season is more likely for much of northeast Australia
  • A wetter than normal season is more likely for Tasmania and the eastern parts of the Pilbara and Gascoyne in WA
  • The chances of a wetter or drier than normal season are roughly equal over the remainder of the country
  • Climate influences include a neutral tropical Pacific, and local sea surface temperature patterns
  • Outlook accuracy is moderate over most of the eastern mainland, the Top End of the NT, and most of WA. Elsewhere, outlook accuracy is low.
Probability of exceeding median rainfall, large image

Details

The chances of exceeding the median rainfall during summer are 30 to 40% over eastern Queensland, northeast NSW, and the eastern Top End of the NT. In other words, the chances of below average rainfall are 60 to 70% over these areas. So, for every ten summer outlooks with similar odds to these, about three or four of them would result in above-average rainfall over these areas, while about six or seven would be below average.

Conversely, the chance of exceeding the median rainfall is greater than 60% over Tasmania, and the eastern regions of the Pilbara and Gascoyne in WA.

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 country.

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 broadscale climate affect Australian rainfall. During summer, historical accuracy shows the outlook to be moderately consistent over much of the eastern mainland, the Top End of the NT, and most of WA. Over western Queensland, eastern WA, and central NSW the outlook is weakly consistent, with the rest of the country only very weakly consistent.