AN ACTIVE monsoon in northern Australia will persist for a while longer increasing the potential for tropical cyclone development to the north east and north west of the continent.
Some moisture will inevitably find its way into the south east states, so the chances of at least average and most likely above average rainfall in much of eastern Australia will remain fairly high into autumn.
The current pulse in the Madden-Julian Oscillation is contributing to increased rainfall potential in the north and most models indicate it will move only slowly to the east and therefore continue to influence our weather for another week or two at least.
- Slightly negative IOD bodes well for autumn
- MJO likely to increase tropical cyclone risk
- La Nina set to weaken as peak is reached
The problem with tropical cyclone formations and movement is that these aspects are very difficult to forecast more than a couple of days ahead.
Cyclone development in the Coral Sea, for example, might form and then move south east dragging moisture away from the continent whereas movement more to the south or south west may result in more severe weather in coastal Queensland but will also increase rainfall potential over large areas of eastern Australia.
Other La Nina type features persist.
The Southern Oscillation Index has completed two months over +15 for the first time since January 2011.
A 10-year break has been quite significant and although the daily contributions to the SOI have started to fall a little, it is expected to remain above the La Nina threshold of around +7 for another couple of months.
The Indian Ocean Dipole remains close to zero (neutral), but has trended very slightly into the negative due to increased water temperatures in the tropical north east Indian Ocean off north west Australia.
As mentioned previously, this has little or no effect on the rainfall in the south east states until around April but the slightly negative readings at times recently is definitely a better sign than the opposite.
Looking beyond the next few months is always a challenge and the scientific basis for six, nine and 12-monthly outlooks is still developmental.
Some longer term analyses coming from research institutes in the US indicated that the La Nina would fade back to a neutral set-up across the Pacific by April, after which the neutral pattern would remain dominant for the rest of the year.
Interestingly, however, is that a few models indicate there could be a slightly increased chance of another La Nina - put at around a one chance in three - by late October while a neutral set-up remains the most likely.
The good news is that the chances of an El Nino any time this year remains even lower.
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