SOME tropical cyclones do more good than harm, and this was the case with cyclone Trevor is recent weeks.
Despite crossing the northern Australia coast twice, near Lockhart River (far North Queensland) as a category 3 system, and then near Boroloola (Northern Territory) as a category 4 cyclone, its areas of impact were fortunately sparsely populated.
It then dragged down considerable moisture providing parts of central Queensland with the best rains for many years.
By the end of last week, mid-level moisture extended into NSW by which time the remnants of Trevor had disappeared off the charts.
But this residual moisture interacted with the first, strong Southern Ocean cold change of the season last Friday night and brought a band of very good rain stretching from the Hunter Valley to the North West Slopes and lighter falls through other drought effected parts of the state, but a few areas missed out.
Such one off events have been referred to by this column in recent times as being slightly more likely than normal in the current season.
However, the same things still apply to them, namely (1) they are often concentrated in small areas, and (2) a greater than normal dependence on them is likely as other climate indicators are not that positive for the next six months.
This is because it is likely that at least a weak El Nino will be in place during the next six months, although the Southern Oscillation Index for March is likely to be around -6 to -7 which is just on the border of an El Nino (it was as low as -14 in February). It was fortunately that in the recent one off event, the area affected by the remnants of Trevor was relatively large.
There is a reasonable chance that further such events will occur, especially in central to northern NSW and Queensland in the coming one to three months but once again, the areas they are likely to effect will be patchy and probably smaller than the recent event. The other feature of a changing climate is variability and this will also apply to temperatures during the second half of autumn and early winter.
Although the seasons are expected to average out a little warmer than normal overall, the occasional quite significant but brief cold spell will become a feature, especially as we get closer to winter.
So, in summary, patchy falls will relieve dry conditions is some areas but an emphasis on the word "patchy" must be noted. Overall, the chance of above average rain for much of south-eastern Australia in the coming three months remains at only about 40 per cent.
