Summary: A developing El Niño
Current Pacific climate patterns are typical for the development phase of an El Niño event. The key indicators include sea-surface temperatures above El Niño thresholds, sustained negative values of the Southern Oscillation Index (SOI), weaker than average Trade Winds during the past two months and increased cloudiness in the central to west Pacific.
However, to qualify as an El Niño event, these key indicators (especially the ocean temperatures) would need to remain at their present levels until the end of the year. There is a strong likelihood that this will occur, given what we know from previous events. Furthermore, most computer models indicate continued warming in the Pacific, implying a strengthening of the developing El Niño pattern.
The observed below average rainfall since late autumn across Australia's southern half, especially in the southeast and southwest, is also consistent with the early stages of an El Niño event. Furthermore, even if El Niño thresholds are not maintained across the range of indicators, a warming Pacific and a low SOI bias the climate towards being drier and warmer than average across eastern and northern Australia for the remainder of 2006. This is reflected in the October-December outlooks for rainfall and temperature.
In Brief
* Pacific climate patterns are indicative of a developing El Niño.
* Equatorial Pacific SSTs have continued to warm and are now over El Niño thresholds.
* Subsurface temperatures have also increased. A Kelvin Wave of increased temperatures is in the eastern Pacific, propagating towards the South American coast.
* The SOI, though still negative, has risen to a current (25th September) 30-day value of −5.
* After being much weaker than normal for nearly a month, the The Trade Winds have been near-normal in the second half of September. However, a strong westerly wind burst is emerging in the western Pacific.
* Cloudiness near the date-line along the equator has been above average so far in September. In general, cloudiness has been increasing in this area since late May.
* A majority of computer models now predict El Niño conditions developing or persisting in the Pacific during the rest of 2006.
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