Seasonal Climate Outlook Message for September to December 2009

The bottom line

Unusual El Nino pattern persists Dave McRae, Qld Climate Change Centre of Excellence, 29/09/09.

According to the latest ENSO Wrap-up from the Bureau of Meteorology an El Nino sea surface temperature (SST) pattern continues to persist in the Pacific. However the current El Nino pattern is unusual in that sea surface temperatures along Australia's northern coastline and throughout the Coral Sea are warmer than average. Normally during an El Nino event, ocean temperatures in these regions are average to cooler than average.

The El Nino SST pattern is also not reflected yet in SOI values. The 30 day average of the SOI as of the 29th September is plus 4.3. Negative SOI values (say below minus 5) are normally associated with El Nino events. SOI values are currently being influenced by the warmer than average sea surface temperatures to the north of Australia.

This then raises the question as what impact will the current El Nino SST pattern have on rainfall across eastern Australia. For example, below average rainfall was recorded throughout most of Queensland during winter. While low rainfall is normal between July and September, July and August this year was particularly dry with a state-wide averaged rainfall of 2.0mm for those 2 months. This breaks the previous record of 2.8mm set in 1946.

As well as being drier than normal, temperatures experienced throughout winter across Queensland where also generally warmer than normal. For example, the average daily temperature experienced during winter was the second highest on record. These warmer than average conditions were also reflected by the state-averaged winter maximum temperature being the warmest on record.

These drier and warmer than normal conditions are what is normally expected during an El Nino. Typically during an El Nino event, there is a lower chance of getting above median rainfall during winter, spring and early summer throughout southern and inland eastern Australia. Therefore there will be much interest in which direction SOI values take as the summer rainfall season approaches.

Interestingly six of the seven leading international climate models surveyed indicate an El Nino climate pattern is likely to persist for the remainder of 2009. None of the surveyed climate models are forecasting any potential return of La Nina or La Nina like conditions. Given that El Nino events (and La Nina's) tend to persist from autumn to autumn, this is not a surprise.

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Last updated: 28 September 2009