It’s a mixed bag as we move towards a weak La Niña
The Bureau of Meteorology has forecast a 50 per cent chance of above-average rainfall for much of Australia from now until the end of January.
And the latest BoM rainfall outlook shows that November to January daytime and overnight temperatures are likely to be warmer than average for most of the country, with the highest chances over Tasmania, Victoria and northern Australia.
Elsewhere, the chance of a warmer three months is close to 50 per cent.
Ocean temperatures have been cooling rapidly in the Pacific Ocean, and this is likely to continue towards La Niña levels over the coming months.
However, given the competing influence of other climate drivers (weakly warm waters to the north of Australia, and cooler waters in the Indian Ocean), current outlooks do not favour widespread rainfall across Australia that is typical of most (two thirds) of past La Niña events.
Ocean temperatures around Australia are forecast to be near average during the November to January period, which is also providing little push towards wetter or drier conditions.
In addition to the natural drivers such as the El Niño-Southern Oscillation and the IOD, Australian climate patterns are being influenced by the long-term increasing trend in global air and ocean temperatures.
“Most models now suggest that La Niña might form by late 2017, so our ENSO Outlook has moved to La Niña Watch,” BOM senior climatologist Dr Andrew Watkins says.
“If La Niña does develop it’s likely to be short lived and much weaker than the last event in 2010 to 2012, when Australia experienced its wettest two years on record.
“The rainfall outlook for November to January is mostly neutral,” Watkins adds.
“That means climate drivers are not pushing us towards a particularly wetter or dryer season than usual.
“When this is the case, rainfall can still range from average to substantially above or below average – but it’s less likely to be at the extreme ends of the scale.”
Looking back to October, Watkins says that, following a very dry winter in many parts of the country, October rainfall was above average in Queensland and northern New South Wales.
“In some areas this produced flooding,” he says. “Bundaberg received its October average rainfall in one day … not just once but three times in the month.
“However, the heavy rains failed to reach some southern areas. Serious rainfall deficiencies remain in parts of New South Wales and South Australia.
“The extra cloud cover over parts of Queensland meant warmer nights than usual in October, but cooler days. On the other hand, much of southern Australia had warmer than average days.”
Soils remain dyer than average for time of year across NSW, eastern Victoria and the eastern agricultural regions of South Australia. Further north, where the most rain fell, soil moisture levels have improved significantly.
Watkins says southern water shortages are nearing the end of their traditional winter filling season.
In Tasmania and the South-West Coast levels are higher than at this time last year (62 per cent vs 56 per cent, and 50 per cent vs 41 per cent, respectively).
However, storages are lower in the Murray-Darling Basin and southern Victoria (73 per cent vs 81 per cent and 51 per cent vs 60 per cent, respectively).
Turning to streamflows, Watkins says that, after a mostly dry winter, “rains in October soaked into dry soils at first so the streamflow outlook for October to December is for mostly near-median or low streamflows – particularly in the east where soils are driest”.
In terms of temperatures, days and nights are likely to remain warmer than average in large parts of northern Australia as well as in parts of the south-east.
A shift towards a weak La Niña can increase the chance of heatwaves for south-eastern Australia.
“Tropical cyclone season also begins in November,” Watkins says. “On average 10 to 13 tropical cyclones develop in our region each year, and about four cross our coast.
“This year’s outlook suggests a typical season is likely.”
A shift towards a weak La Niña can increase the chance of heatwaves for south-eastern Australia
The chance of above-median maximum temperature for November to January. Source: BOM Rainfall totals that have a 75 per cent chance of occurring for November to January. Source: BOM Photo: Southern Lightscapes-Australia/Moment/Getty Images Photo: Mariusz Kluzniak/Moment/Getty Images