The tropical north of Australia and western Western Australia are more likely to have a wetter autumn than average, according to the Bureau of Meteorology’s latest three monthly seasonal outlook.
The report also suggests that parts of southeast South Australia and western New South Wales are likely to have a drier season from March to May.
The drivers of the outlook are a warmer than normal Indian Ocean and cool conditions in the tropical Pacific associated with La Niña.
The chances of receiving above median rainfall during the February to April period are above 60pc over the tropical north of Australia and western WA).
Probabilities rise to between 70 and 75pc over parts of western WA, particularly the Gascoyne region.
Such odds mean that for every ten years with similar ocean patterns to those currently observed, about six or seven years would be expected to be wetter than average over these areas, while about three or four years would be expected to be drier during the February to April period.
Conversely, the chances of receiving above normal rainfall are between 35 and 40pc over southeast SA, the far southwest of Queensland and far western of NSW.
“In other words, the chances of below normal rainfall is between 60 and 65pc,” the bureau reports.
“However, the outlook skill is not high over these regions, so this outlook should be used with caution.”
Over the rest of the country, the chances of a drier or wetter February to April are roughly equal.
La Niña conditions persist across the tropical Pacific. Computer models surveyed by the Bureau suggest the current La Niña event will persist through the remainder of the southern hemisphere summer and early autumn.
The national outlook averaged over February to April 2012 shows that warmer days are more likely over southeastern Australia, cooler days and nights are more likely over northwestern Australia and warmer nights are more likely over northeastern and southwestern Australia.
The chance that the average February to April maximum temperature will exceed the long-term median maximum temperature is 60 to 70pc over southeast SA, southern NSW, Victoria and Tasmania.
This means that for every ten years with ocean patterns like the ones currently observed, about six or seven February to April periods would be expected to be warmer than average in these areas, with about three or four being cooler.
“The user should note that skill is patchy in this area, particularly over SA and NSW,” the bureau said.
In contrast, there is a 40pc chance of warmer than normal days over the eastern interior of WA, near the NT border. In other words, there is a 60pc chance of cooler days over this region.
The chance that the average minimum temperature for February to April will exceed the long-term median minimum temperature is above 60pc across northern Queensland and the southwest half of WA. Probabilities exceed 80% across the Gascoyne region of WA.
Conversely, there is a 25 to 40pc chance of warmer than normal nights over northern WA, the southern NT, southwest Queensland and northern SA. This means there there is a 60 to 75pc chance of cooler nights over this region.
History shows the oceans' effect on minimum temperatures during the February to April period to be moderately consistent over northern parts of Australia, Tasmania, the southern half of SA and southwest WA. Over the remainder of the country skill is only weakly to very weakly consistent. Users should exercise caution when using this outlook in these areas of low skill.