National rainfall outlook

Issued 23 October 2013

Drier season more likely for northeast Australia

Text commentary of chance of increased rainfall

Summary

  • A drier than normal season is more likely for most of northeastern Australia
  • The chances of a wetter or drier than normal season are roughly equal over the remainder of the country
  • Climate influences include locally warm sea surface temperatures around most of Australia, and a neutral tropical Pacific
  • Outlook accuracy is moderate over most of the eastern States, and northern and western WA. Elsewhere, outlook accuracy is weak.
Probability of exceeding median rainfall, large image

Details

The chances of exceeding the median rainfall during November to January are 30 to 40% over most of Queensland, most of the NT, northeast SA and northern NSW. In other words, the chances of below average rainfall are 60 to 70% over these areas. So, for every ten November to January 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.

The chance of receiving a wetter or drier than normal November to January 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 remainder of spring and summer. This means there is no strong shift in the odds from the tropical Pacific in this outlook.

The Indian Ocean Dipole (IOD) is neutral, and is expected to remain so for the next month. Beyond that time, the effect of the IOD on Australian climate from December through to April is limited, and is therefore not an influence in the outlooks during this period.

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

How accurate is the outlook?

Outlook accuracy is related to how consistently the oceans and broadscale climate affect Australian rainfall. During the November to January period, historical accuracy shows the outlook to be moderately consistent over most of the eastern States, and northern and western WA. Over the Top End of the NT, and western Queensland the outlook is weakly consistent, with the rest of the country only very weakly consistent.