|Northern Aust Seasonal Rainfall Outlook: probabilities for February to April 2009, issued 22nd January 2009|
Mixed odds for late summer to mid-autumn rainfall
The northern region outlook for total late summer to mid-autumn (February to April) rainfall shows mixed odds for exceeding the seasonal median. There is a shift in the odds to lower than median rainfall over parts of central and northern Queensland, while there is a slight shift in the odds favouring above median rainfall over the northern NT/WA border region.
The cooling trend in the Indian Ocean in late 2008 is the dominant factor in this rainfall outlook.
The chance of exceeding median rainfall over much of central and northern Queensland are between 20 and 40%, which means that these areas have a 60 to 80% chance of being drier than normal. This means that for every ten years with similar ocean patterns, about six to eight years are expected to be drier than average in this region, while about two to four years are expected to be wetter.
In contrast, the odds of exceeding median rainfall over the northern NT/WA border region is about 60%, which means this area has a 40% chance of being drier than normal.
Outlook confidence is related to how consistently the Pacific and Indian Oceans affect Australian rainfall. During the February to April period, history shows the effect to be moderately consistent through the central and northern parts of both Queensland and the NT. Elsewhere the effect is only weakly or very weakly consistent (see background information).
The central and eastern equatorial Pacific Ocean cooled further during December. This brings the Pacific Ocean into line with atmospheric indicators, a number of which have been approaching La Niña levels since October 2008. However, most current model outlooks, and a build-up of warmer sub-surface water in the western equatorial Pacific, suggest that the cooler conditions in the Pacific may not persist beyond summer 2009. The most likely scenario is for the central and eastern Pacific to warm over the coming months and hence remain neutral. The SOI remains positive at approximately +13 for the 30 days ending 19 January. 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.
More information on this outlook is available 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 20th February 2009