No La Nina Yet. Dave McRae 20/08/07
According to the Bureau of Meteorology in their "ENSO Wrap-up" (available at www.bom.gov.au) the past three months have seen conditions in the Pacific Ocean fluctuate without any consistent trend towards either a La Nina or El Nino being apparent.
For example during July there where periods of weakening and strengthening south east trade winds, falling and rising SOI values (30day average of the SOI value varied from +4.2 to -11.9) and warming and cooling ocean temperatures.
While the latest runs from the computer models continues to indicate a reasonable chance for a La Nina to develop in 2007, there needs to be some significant changes in our background climate drivers.
This would include consistently stronger than average south east trade winds, positive SOI values and further cooling of the eastern equatorial Pacific Ocean. Interestingly during the last few weeks there has been some evidence of these type of changes starting to occur. However it is too early to state that this is the beginning of a sustained trend.
So while the climate models the Bureau of Meteorology have reviewed do indicate an increased chance of a La Niña developing, they also suggest the event is likely to be weak and persist for only a few months. It is also starting to get late in the year for a La Nina to develop.