Northern Australian rainfall outlook

Issued 22 May 2013

A wetter dry season likely for northern Australia

Summary

  • A wetter than normal June to August period is more likely for most of northern Australia
  • Chances of above or below normal rainfall are roughly equal over the Roper-McArthur, Gulf Country and the north Tropical Coast
  • Climate influences include a warmer than normal eastern Indian Ocean, a neutral tropical Pacific, and warm sea surface temperatures across the north
  • Forecast skill is moderate over most of north-eastern Australia, except for the far south of the NT, and the far north Cape York Peninsula.
Probability of exceeding median rainfall, large image

Details

The chances of above-median winter rainfall are 60 to 70% over a broad area of northern Australia including the Top End, the far north Cape York Peninsula, the southern NT and Queensland (see map above). Such odds mean that for every ten years with similar climate patterns to those currently observed, about six or seven years would be expected to be wetter than average over these areas, while about three or four years would be drier. However, for many areas in the north, the median June to August rainfall is between 0 and 1 mm and even a small amount of rain would be enough to exceed the median.

Climate influences

The tropical Pacific has remained ENSO-neutral since mid-2012. Climate models surveyed by the Bureau of Meteorology suggest sea surface temperatures in the tropical Pacific Ocean are likely to sit on the cool side of neutral throughout the dry season.

Four of five international models surveyed by the Bureau favour the development of a negative Indian Ocean Dipole (IOD) event sometime in late 2013. A negative IOD increases the chances of above normal humidity levels and rainfall over northern and central Australia during the dry season. In addition, warmer than normal sea surface temperatures currently surround northern Australia. Warmer ocean temperatures can provide more moisture to the atmosphere, which in favourable weather conditions may result in increased rainfall.

How accurate is the outlook?

Outlook confidence is related to how consistently the oceans and broadscale climate affect Australian rainfall. During June to August, model accuracy shows the outlook to be moderately consistent over most of the NT and Queensland, except for the far south of the NT, and the far north Cape York Peninsula.