National rainfall outlook

Issued 24 April 2014

Wetter season more likely for much of WA

Text commentary of chance of increased rainfall

Summary

  • A wetter than normal season is more likely for the southern two-thirds of WA and the far southeast of Australia
  • A drier than normal season is more likely for some parts of the northern tropics
  • The chances of a wetter or drier than normal season are roughly equal over the majority of Australia
  • Climate influences include a warming tropical Pacific, and a warm Indian Ocean
  • Outlook accuracy is moderate over large parts of Australia, with low accuracy generally over northwest Australia and parts of outback SA.
Probability of exceeding median rainfall, large image

Details

The chances of exceeding the median rainfall during May to July are greater than 60% over southern and western WA. Chances rise to 65 to 70% over the southwest and Pilbara regions of WA (see map above). For every ten May to July outlooks with similar odds to these, about six or seven of them would result in above-average rainfall over these areas, while about three or four would be below average.

Conversely, the chance of exceeding the median rainfall is less than 40% over the Top End of the NT, and the northern tip of Queensland. In other words, the chances of below average rainfall are greater than 60% over these areas. However, it should be noted that average rainfall at this time of year is far less than is received during the summer months for most of northern Australia (see Rainfall averages tab).

Over the rest of the country, there is no significant shift in the odds towards either a wetter or drier than normal season.

Climate influences

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

Sea surface temperatures in the eastern Indian Ocean, to the south of Australia, and in parts of the Tasman Sea are currently warmer than normal, and are generally expected to remain warm through the forecast period. The warmer waters to the west of the continent may lead to increased evaporation and cloudiness, and hence a wetter than normal outlook for parts of the west. These warmer waters surrounding Australia are not typical of El Niño, and may be somewhat negating the effect of the developing El Niño on the eastern regions.

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 May to July period is:

  • Moderate over western and southern WA, the southern NT and eastern Australia
  • Low to very low over most of eastern WA, the northern half of the NT, and outback SA