|Southeastern Aust Seasonal Rainfall Outlook: probabilities for Summer 2007/2008, issued 22nd November 2007|
Increased summer rainfall for eastern & northern NSW
For southeastern Australia, the outlook for total summer rainfall (December to February), shows a moderate shift in the odds favouring above average totals in eastern and northern NSW.
The pattern of seasonal rainfall odds across eastern Australia is mainly a result of continuing higher than average temperatures over parts of the tropical and sub-tropical Indian Ocean, with a smaller contribution from cooler than average temperatures in the equatorial central to eastern Pacific.
The chances of exceeding the median rainfall for summer are between 60 and 70% in the east and northern inland areas of NSW (see map). In other parts of southeastern Australia, the chances of exceeding the three-month median rainfall are between 45 and 60%, except in southwest Victoria where the probabilities drop to around 40% along the coastal fringe.
So for every ten years with ocean patterns like the current, about six or seven summers are expected to be wetter than average in eastern and northern NSW, while about three or four are drier.
Outlook confidence is related to how consistently the Pacific and Indian Oceans affect Australian rainfall. During summer, history shows this effect to be moderately consistent across much of the eastern half of NSW and the southern half of Victoria (see background information). Elsewhere the effect is generally only weakly or very weakly consistent.
A late-developing La Niña event is in progress across the Pacific Basin and computer models indicate it will persist at least until the early part of 2008. The 30-day value of the Southern Oscillation Index (SOI) was +11 as at 19th November. 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, NSW, SA, Victoria and Tasmania at the following numbers:
THE NEXT ISSUE OF THE SEASONAL OUTLOOK IS EXPECTED BY 17th DECEMBER 2007