|National Seasonal Rainfall Outlook: probabilities for Autumn 2009, issued 20th February 2009|
Wetter autumn favoured for northern Queensland
The national outlook for total autumn rainfall, shows mixed odds for exceeding the seasonal median. There is a moderate shift in the odds favouring higher than normal rainfall over much of northern Queensland and southeastern SA. Conversely, there is a moderate shift in the odds favouring lower than normal rainfall over the southwest corner of WA.
The pattern of seasonal rainfall odds across Australia is mainly a result of warm conditions in the Indian Ocean in January, the Pacific Ocean had little contribution to this forecast.
The chance of exceeding median rainfall over northern Queensland and southeastern parts of SA during autumn is between 60 and 70%. This means that for every ten years with ocean patterns like the current, about six or seven years are expected to be wetter than average in these regions, while about three or four years are expected to be drier.
In contrast, the odds of exceeding median rainfall over the southwest corner of WA are around 40%, which means that these areas have a 60% chance of being drier than normal.
Across the rest of the country, the chance of exceeding the median rainfall during autumn is between 40 and 60%, meaning that above average falls are about as equally likely as below average falls in these regions.
Outlook confidence is related to how consistently the Pacific and Indian Oceans affect Australian rainfall. During autumn, history shows the effect to be moderately consistent across much of the west and the north of the country. Elsewhere the effect is only weakly or very weakly consistent (see background information).
Some warming of the equatorial Pacific Ocean occurred in January, following cooling in December, so that sea surface temperatures (SST) in the central Pacific have now eased back to neutral values. While sub-surface waters are cool in the eastern Pacific, those in the west of the basin are warmer than normal and there are indications that these will impact on the surface in coming months. Furthermore, most current model outlooks suggest further warming in the Pacific. The most likely scenario is for conditions to remain neutral. The SOI remains positive at approximately +15 for the 30 days ending 17 February. 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 detailed forecast maps, including the probabilities of seasonal rainfall exceeding given totals, can be found here.
|The following climate meteorologists in the National Climate Centre can be contacted about this outlook: Lynette Bettio on (03) 9669 4165, Brad Murphy on (03) 9669 4409, David Jones on (03) 9669 4085,|
Regional commentary is available from the Climate Services Sections in the Bureau's Regional Offices:
THE NEXT ISSUE OF THE SEASONAL OUTLOOK IS EXPECTED BY 24th March 2009