Seasonal Climate Outlook Message for February to May 2008

The bottom line

MJO powers up the monsoon

The monsoon trough has been re-established across northern Australia with this passage of the MJO through the tropics. The MJO is in Phase 5. Much of Queensland is expecting rain over the next few days.

During summer northern Australia can expect MJO enhanced rainfall probabilities Phases 4 through 7 during summer. We expect to see a greater impact from the MJO on our (northern Australian) rainfall during our summer and autumn.

The MJO often initiates the onset of the Australian monsoon, and is also associated increased rainfall for northern Australian. During summer the MJO is typically associated with Southern Hemisphere tropical storms, and cyclones in the Indian Ocean and western Pacific Ocean. A cyclone watch is current (Tuesday 12 February) for northern WA.

The MJO is a tropical band of low air pressure originating off the east coast of central Africa travelling eastward across the Indian Ocean and northern Australia roughly every 30 to 60 days. While the MJO is restricted to the tropics it affects areas well out of the tropics via teleconnections. This means that systems like the MJO interact with other weather and climate systems.

The MJO influences and is influenced by these other factors. Research has shown the MJO to be a useful indicator of the timing of potential rainfall events in Australia. For more information try www.apsru.gov.au/mjo/ or www.bom.gov.au

A mature La Nina event continues in the Pacific basin. Most models show equatorial SST's staying cooler than normal until at least autumn. Sea surface temperatures around the Australian coastline are anomalously warm, helping to induce the flow of moist air across the continent.

As at 11 February the 30 day average of the SOI was plus 11.6.

The 30 day average of the SOI remained positive through January, and was plus 12.7 for the month. The SOI Phase for January was 'Consistently Positive' (Phase 2). The outlook for February to April shows a 50 to70 % chance of above median rainfall for most of Australia.

Some regions, particularly along the southern coast, only have a 40 to 50% chance of exceeding median rainfall. Further isolated southern coastal areas only have a 30 to 40 % chance of exceeding their median February to April rainfall.

Further analysis indicates rainfall for much Australia is more likely to be close to or above the long term average (or middle third to upper third) rather than below or well below average. The Bight coastal regions are more likely to be below average, rather than close to or above average.