Picking up from this thread from July of this year, as indicated in this table from the
Australian Bureau of Meteorology (BOM), the Southern Oscillation Index (SOI) for July,
August and September were strongly positive.
See
http://www.bom.gov.au/climate/current/soihtm1.shtml
This and other observations indicate we are experiencing a La Niņa event
and the high amounts of rain fall of late along the East Coast are testimony to
this.
In a report issued on 29th Sept 2010, BOM reports -
Quote:
A La Niņa remains well-established in the Pacific. Given the current strength of the event and the outlook from long-range models surveyed by the Bureau, this La Niņa is expected to persist into at least early 2011.
All indicators remain firmly at La Niņa levels. The central Pacific Ocean is cooler than the long-term mean both at and below the surface, the Southern Oscillation Index (SOI) remains strongly positive, trade winds are stronger than normal and cloudiness over the central tropical Pacific continues to be suppressed. Such consistent signals indicate the tropical atmosphere and ocean are now clearly reinforcing each other.
La Niņa periods are generally associated with above normal rainfall during the second half of the year across large parts of Australia, most notably eastern and northern regions. Night time temperatures are historically warmer than average and Tropical Cyclone occurrence for northern Australia is typically higher than normal during the cyclone season (November-April).
A negative IOD event is also underway in the Indian Ocean. Negative IOD events often coincide with La Niņa events, and are often, but not always, associated with above average rainfall over large areas of southern Australia during spring. IOD events generally decay in the months of November and December with the onset of the Australian monsoon.
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Full report here -
http://www.bom.gov.au/climate/enso/
In the
National Seasonal Rainfall Outlook issued by BOM on 23rd Sept -
Quote:
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Originally Posted by BOM
The Australian rainfall outlook for the December quarter (October to December) favours wetter than average conditions over large parts of the continent, with strongest odds across northern Australia.
The October to December outlook is the result of warm conditions in the Indian Ocean and cool conditions in the equatorial Pacific Ocean, both of which are associated with the current La Niņa event.
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This chart
http://www.bom.gov.au/climate/ahead/...b.gif?20100923
is a prediction for Oct to Dec 2010 that indicates the probability of a given region
exceeding the median rainfall.