Welcome to the Climate and Water Outlook for October–December 2017.
Some climate drivers are tipping our weather towards drier than average in the coming months,
but others are pushing towards slightly wetter.
First, let's look at recent conditions.
After one of the driest and warmest winters on record for much of Australia, spring has also
started off dry in many parts.
September rainfall has been well below average for most of the country.
Some key agricultural regions of New South Wales and Queensland have only had a third
of their normal September rainfall.
As a result, rainfall deficiencies since March remain at serious to severe levels in parts of
central New South Wales, southeast Queensland and Western Australia.
Many of these same areas have also seen exceptional early spring heat.
Sunny days, dry soils and slow-moving weather systems have seen warm air build up over central
and western Australia, then move over to the east.
Australia had its hottest September day on record on the 22nd.
The next day, New South Wales had its hottest September day on record.
Further heat continued late in the month.
In contrast, clear nights led to frost especially in southeastern Australia during August and
early September, damaging crops and making them more susceptible to later heat.
Further north in New South Wales, Queensland and central Australia, persistent dry and
warm conditions mean lower-level soils are now very dry.
Drier soils can enhance heatwaves, as the soil and the air above it heat up quicker
when there’s little water to evaporate.
Water storage levels in the northern Murray–Darling Basin, where it’s been particularly dry,
have not increased over the past month—nearing the end of the filling season.
Those in the wetter southern regions have risen slightly.
So what's driving our climate right now?
We’re seeing competing influences on Australia’s rainfall from the oceans to our east and west.
The Pacific Ocean has cooled recently in some tropical areas, and half of the models we survey are
pointing towards a borderline or weak La Niña by the summer.
La Niña can result in increased spring and summer rainfall for eastern Australia.
But for the Indian Ocean, half of the models expect a weak positive Indian Ocean Dipole
in spring—warmer waters near Africa than near Australia.
That would typically mean drier conditions over southern and central Australia.
These opposing climate drivers mean the rainfall outlook for October–December shows roughly
equal chances of wetter or drier than average conditions.
That doesn’t mean everywhere will see average rainfall; some places will have above average,
some below—depending on local weather conditions.
In fact, the one-month outlook indicates a wetter-than-average October in eastern and
central Australia and drier in the west is likely.
Keep in touch with local forecasts for more details.
Either way, streamflows remain affected by the dry soils and warm temperatures in many areas.
Near-median to low streamflows are expected for September–November, particularly in the east.
In terms of temperatures: Days and nights are likely to remain warmer than average for
large parts of northern and western Australia, as well as in the southeast.
Vegetation that grew in the wet of 2016 is now drying out, raising bushfire potential
for many parts of Australia.
Significant early season fires have already occurred in Queensland and as far south as Jervis Bay.
More details are available on the Bushfire and Natural Hazards CRC website.
So in summary: The final months of 2017 are likely to be warmer than average over most
of the north and southeast; rainfall is likely to vary across the country,
with our climate drivers having opposing impacts; bushfire and heatwave risk is raised in many areas;
and near-median to low streamflows are expected at most locations.
For more details, visit our website at bom.gov.au/climate/ahead.
You can also get updates via Facebook and Twitter.
For your first look at November–January, our mid-month outlook will be available on Thursday 12 October.
For the Bureau of Meteorology, I’m Paul Feikema.