|Northern Aust Seasonal Rainfall Outlook: probabilities for August to October 2008, issued 25th July 2008|
Mixed rainfall odds for late winter to mid spring
The outlook for northern Australia for total August to October rainfall shows generally moderate swings in the odds towards below-normal rainfall in much of north and west Queensland. In contrast, higher than average rainfall is slightly favoured in the northwest of NT.
The pattern of seasonal rainfall odds across northern Australia is a result of a continued strong warming trend in the central and southeastern Indian Ocean, off the west coast of WA, and a warming trend in recent months over the equatorial Pacific.
The chances of exceeding the median rainfall over the August to October period are between 25 and 40% over much of northern and western Queensland (see map). This means the chances of below average rainfall are between 60 and 75% in these areas.
So in years with ocean patterns like the current, about six to seven August to October periods out of ten are expected to be drier than average in these parts of Queensland, while three to four are wetter. However it should be noted that this is a seasonally drier time of year in northern Queensland. In the northwest of NT the chances of exceeding the median rainfall are between 55 and 60% for the August to October period.
Over the remainder of northern Australia, late-winter to mid spring rainfall totals have a 40 to 55% chance of exceeding the three-month median. So the chances of being wetter than normal are about the same as the chances of being drier.
Outlook confidence is related to how consistently the Pacific and Indian Oceans affect Australian rainfall. During August to October, history shows this effect to be moderately consistent across most of Queensland and the east and north of the NT. Elsewhere, it is generally weakly consistent, reaching moderate only in patches (see background information).
The 30-day value of the Southern Oscillation Index (SOI) was +3 as at 22 July. Computer models indicate a continuation of neutral conditions across the equatorial Pacific Ocean as the most likely outcome during the forecast period. For routine updates and comprehensive discussion on any developments please see the ENSO Wrap-Up.
Click on the map above for a larger version of the map. Use the reload/refresh button to ensure the latest forecast map is displayed.
More information on this outlook is available Monday to Friday from 9.00am to 5.00pm local time by contacting the Bureau's Climate Services sections in Queensland and the Northern Territory at the following numbers:
THE NEXT ISSUE OF THE SEASONAL OUTLOOK IS EXPECTED BY 27th August 2008