Mixed El Nino signals in Australia; development slows

An El Nino climate episode in the Pacific Basin is showing mixed signals with its development slowing in the past two weeks, the Australian government's Bureau of Meteorology reported Wednesday (August 19).

Furthermore, a coupling between the Pacific Ocean and atmosphere which amplifies and maintains El Nino events has so far failed to eventuate, with a neutral Southern Oscillation Index, or SOI, and sub-surface cooling of the Pacific Ocean being evidence of this, it said.

Still, the trade winds are weakening over a broad area, which might promote renewed warming of the ocean, and "leading climate models continue to predict further development of the El Nino, although not as emphatically as a month or two back, it said.

"Therefore, the odds remain strongly in favour of 2009 being recognized as an El Nino year," the bureau said in a weekly review of indicators.

The SOI has been falling steadily since the middle of January, and now measures -4 for the 30 days ended Aug. 16, down from a peak of +12 on July 19. The average SOI in July was +2, it reported. Typically, sustained negative values for the SOI, say around -10, are associated with an El Niño.

"Six of the seven leading international climate models surveyed by the Bureau predict the tropical Pacific to continue to warm and to remain above El Niño thresholds for the remainder of 2009," it said.

El Nino periods are usually but not always associated with below normal rainfall in the second half of the year across large parts of southern and inland eastern Australia.