Seasonal Climate Outlook Message for September to December 2009

The bottom line

El Nino SST persists Dave McRae, Qld Climate Change Centre of Excellence, 14/09/09.

According to the latest ENSO Wrap-up from the Bureau of Meteorology www.bom.gov.au/climate/enso an El Nino sea surface temperature pattern continues to persist in the Pacific.

Sea surface temperatures (SST's) throughout most of the tropical Pacific Ocean remain significantly warmer than the long term average and are above El Nino thresholds throughout the central and eastern equatorial Pacific.

This pattern is also consistent with the output of the leading international climate models. Six of the seven 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.

Of more interest is that monthly values of the SOI have remained near zero. This indicates that the atmosphere is not yet reflecting the El Nino SST pattern. Usually during El Nino events, negative SOI values (for example below minus 5) are experienced. A consistently negative SOI phase at this time of year would mean a significant reduction in the chance of getting above median rainfall. The 30day average of the SOI as of the 14th September is plus 0.1.

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.

The last passage of the Madden-Julian Oscillation or MJO across northern Australia occurred during late August/early September. Therefore the next passage of the MJO would be expected around mid-October.

The MJO is a band of low air pressure which originates off the east coast of central Africa. It travels eastward across the Indian Ocean and northern Australia roughly every 30 to 60 days. Because of the timing of the MJO the phenomenon is also known as the forty day wave. It can be used as an indicator for the timing of potential rainfall events.

The impact of the MJO on rainfall varies between the different seasons and location. For example the MJO has a greater influence on rainfall throughout northern Australia during summer and southern Australia during winter. For more information on the MJO go to www.bom.gov.au

The latest rainfall probability maps are available at www.longpaddock.qld.gov.au

You can receive a text message with the latest SOI values sent to your mobile phone. To subscribe to this free service, call me on (07) 4688 1459 or e-mail david.mcrae@climatechange.qld.gov.au

The full story

SOI remains in "Near Zero Phase" for third month in row. Dave McRae, Qld Climate Change Centre of Excellence, 31/08/09.

Based on the shift in the monthly value of the SOI from plus 2.0 for July to minus 3.9 for August, the SOI is in a "Consistently Near Zero" phase.

An analysis of a Consistently Near Zero SOI phase at the end of August and rainfall records for September to November indicate a 30 to 50% chance of getting above the long term median rainfall throughout northern, central and western Queensland. Across the south east quarter of the state, the chance of getting above the long term median rainfall for the same period is marginally higher at 50 to 60%.

Based on these probabilities, this forecast would not be regarded as indicating a high chance of getting well above average rain during September to November. It's also worth remembering that we are still in our "traditional dry season" of August and September.

These months have the lowest median monthly rainfall totals for most locations in Queensland. For example median rainfall for August and September at Blackall is 9 mm and 6 mm, at Emerald is 11 mm and 9 mm, at Goondiwindi is 26 mm and 34 mm, at Toowoomba is 33 mm and 41 mm and Mareeba is 2 mm and 2 mm.

For those interested in following historical patterns more closely, some of the years that have had the same SOI pattern at the end of August include 2004, 2003, 2001, 1999, 1995, 1992, 1990, 1984, 1980, 1978, 1969, 1968, 1963, 1961, 1959 and 1952.

It can be useful to find out what rainfall and farming conditions where like in your area for September to November in those years. Information on what rainfall patterns where like in those years is available at www.longpaddock.qld.gov.au or in Rainman StreamFlow.

It will be interesting to see what the SOI does over the next few weeks. If it remains in a "Near Zero" phase through to the end of the September there is an increase in the likelihood or chance of severe storm activity across the southern half of Queensland and northern New South Wales.

When using a climate forecast you should remember that the probability or percent chance of something occurring is just that - a probability. For example if there is a 70% chance of recording more than 100 mm there is also a 30% chance of recording less than 100 mm i.e. 70-30; 30-70. It does not mean that you will get 70% more than 100 mm or 100 mm plus another 70%.

The last passage of the Madden-Julian Oscillation or MJO across northern Australia occurred during late August/early September. Therefore the next passage of the MJO would be expected around mid-October.

The MJO is a band of low air pressure which originates off the east coast of central Africa. It travels eastward across the Indian Ocean and northern Australia roughly every 30 to 60 days. Because of the timing of the MJO the phenomenon is also known as the forty day wave. It can be used as an indicator for the timing of potential rainfall events.

The impact of the MJO on rainfall varies between the different seasons and location. For example the MJO has a greater influence on rainfall throughout northern Australia during summer and southern Australia during winter.

According to the latest ENSO Wrap-up from the Bureau of Meteorology www.bom.gov.au/climate/enso an El Nino sea surface temperature pattern continues to persist in the Pacific.

Sea surface temperatures (SST's) throughout most of the tropical Pacific Ocean remain significantly warmer than the long term average and are above El Nino thresholds throughout the central and eastern equatorial Pacific.

This pattern is also consistent with the output of the leading international climate models. Six of the seven 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.

Of more interest is that monthly values of the SOI have remained near zero. This indicates that the atmosphere is not yet reflecting the El Nino SST pattern. Usually during El Nino events, negative SOI values (for example below minus 5) are experienced. A consistently negative SOI phase at this time of year would mean a significant reduction in the chance of getting above median rainfall. The 30day average of the SOI as of the 14th September is plus 0.1.

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.

According to the Bureau of Meteorology (www.bom.gov.au) seasonal climate summary for Queensland, below average rainfall was recorded throughout most of the state during winter. While low rainfall is normal between July and September throughout Queensland, 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. August 2009 was also Australia's warmest on record.

You can receive a text message with the latest SOI values sent to your mobile phone. To subscribe to this free service, call me on (07) 4688 1459 or e-mail david.mcrae@climatechange.qld.gov.au