Seasonal Climate Outlook September - November 2007
The latest rainfall outlook was released by the Bureau of Meteorology on 23 August. The outlook for total spring rainfall generally shows no strong swings in the odds towards wetter or drier conditions in south-east Australia. However, there is a moderate shift in the odds favouring a drier than average spring in south-west Victoria and south Gippsland. The chance of accumulating at least average rainfall is 35-40% in the State’s south-west increasing to 45% in the north and 50% in the east.
Averaged over spring, the chances are between 60 and 65% for above-normal maximum temperatures over much of Victoria.
The Bureau issued the latest ENSO Wrap-Up on 29 August. Since late July there has been a gradual strengthening of most indicators to near La Niña thresholds. Overall, there was further cooling of the ocean in the eastern equatorial Pacific, normal to stronger than normal Trade Winds and less than average cloudiness from July to August. Furthermore, the SOI remains at +2, a modest rise from -4 for July.
However, the Bureau reports that further cooling of the ocean remains unlikely as computer model guidance suggests ocean temperatures will remain near La Niña thresholds until the end of the year. Historically, most significant La Niña events are firmly established by winter’s end.
For a La Niña to develop in 2007 the SOI needs to rise to around +7 for several months and the present patterns of La Niña indicators maintained.