Summary: A strengthening El Niño
There was a general strengthening of all ENSO indicators during October. What will become known as the 2006/07 El Niño, has now developed and is primed to enter the maturing phase, which is characterised by self-sustaining feedback between the Pacific ocean temperatures, winds and cloud patterns. Computer model guidance indicates that Pacific Ocean temperatures are likely to peak around January or February 2007.
What does this mean for Australia? Generally speaking the main impact on rainfall is during winter and spring, with a switch towards wetter conditions having been common, but by no means guaranteed, in January or February during previous El Niño events. For example, widespread moderate to heavy rain fell in February 2003 at the end of the 2002/03 El Niño event, while a similar pattern occurred in January 1995 after the peak of the 1994/95 event. In contrast, there was only patchy relief at the end of the 1965/66 event, with a substantial change in the rainfall patterns not occurring until August 1966. Readers are referred to Australian rainfall patterns during El Niño events as a guide as to how the next few seasons might pan out.
Much cooler than normal tropical ocean temperatures to the north and northwest of the continent, have also played an important role in the drier than average conditions over eastern and southern Australia during recent months.
As for temperatures, the November to January seasonal outlook indicates a moderate to strong likelihood of above-normal temperatures across the eastern half of the country. Furthermore, El Niño events are associated with an increase in the number of extreme fire-risk days over southeastern Australia, that is, days which are hot, dry and windy.
Noteworthy features of the Pacific climate during October were (a) weaker or much weaker than average Trade Winds over most of the basin for most of the month; (b) warming of 0.5 to 0.7°C near South America and by about 0.2°C elsewhere along the equatorial Pacific; (c) a marked drop in the SOI to around −15 or slightly lower; (d) an increase in cloudiness over the western to central Pacific; and (e) further warming of the Pacific sub-surface.
In Brief
* Pacific climate patterns show an intensifying El Niño.
* Equatorial Pacific SSTs have been warming and are over El Niño thresholds.
* Subsurface temperatures have remained warm and have increased in response to a strong westerly wind burst.
* The SOI has fallen to a current (30th October) 30-day value of −15.
* Trade Winds remain much weaker than normal in the western to central Pacific.
* Cloudiness near the date-line has been increasing since late May and was much higher than average in October.
* Computer models are nearly unanimous in predicting El Niño conditions for the rest of 2006 and early 2007.
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