Welcome to the Climate and Water Outlook for summer 2017–2018.
While La Niña looks likely during summer, it's expected to be short-lived and have
less effect on rainfall and temperatures than recent La Niña events.
But first, let's look at recent conditions.
Spring saw a mixture of both very dry and very wet periods.
After a dry start to the season in eastern Australia,
October turned very wet in Queensland and northern New South Wales.
In November, tropical air from the north fed thunderstorms through central Australia and
into the southeast.
In some places, rainfall was extremely heavy—coming at the wrong time for the 2017 harvest.
The heavy spring rain helped ease rainfall deficiencies in northern areas, but serious
deficiencies remain in parts of the southeast.
Spring has been warmer than average in most areas.
September set records for extreme temperatures, but November has seen record-long periods
of warmth, particularly in the southeast.
Melbourne had a record run of nine consecutive November days over 28°C,
while Hobart had six days in a row over 26°C, equalling its record for any month.
The warm and calm conditions led to exceptional ocean temperatures, with waters off Victoria
and Tasmania warming up to 3°C above normal—a record for November.
Despite this warmth, a burst of cold air in early November brought late frosts that
damaged crops ready for harvest, particularly in western Victoria and eastern South Australia.
Soil moisture has responded quickly to recent rains, but is still drier than average in
those parts of the south that missed out.
Going into summer, water storage levels in Tasmania and the South West Coast are higher
than at this time last year; but in the Murray–Darling Basin and across southern Victoria,
storage levels are lower.
So what's driving our climate right now?
Our ENSO Outlook has been raised to La Niña ALERT, which means there's
three times the normal chance of La Niña this summer.
While La Niña normally brings above-average rainfall to Australia, if it develops this summer
it’s likely to be short-lived and weak.
The tropical Pacific Ocean is showing a typical La Niña pattern, but the big difference this year is
the ocean temperatures around northern Australia and in the eastern Indian Ocean.
Both would normally warm during La Niña, but this time they are forecast to stay average
or even cooler than average, which is less likely to drive widespread rain over Australia.
As a result, the summer rainfall outlook is neutral for much of the country, although
above-average rainfall is likely for parts of the southeast.
For streamflows, mostly low and near-median flows are expected for November–January,
largely across southern Australia.
High flows for this time of year are forecast for much of coastal Queensland, following
high spring rainfall.
In terms of temperatures, days and nights are likely to remain warmer than average for
large parts of central and southeastern Australia.
A shift towards a weak La Niña can make periods of warm weather in southern Australia
hang around much longer.
Check our website to see heatwave forecasts for the week ahead.
The seasonal bushfire outlook for southern Australia was updated at the end of November.
Bushfire potential remains above average in several southern areas, including close to capital cities.
So, in summary, summer is likely to be warmer than average over large parts of central and southeastern
Australia; the rainfall outlook is neutral for much of the country; and
low to near-median 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.
Our next video will be released on Thursday 21 December.
For the Bureau of Meteorology, I’m Paul Feikema.