If you thought the torrential rain in Sydney might be a one off not to be repeated again this year, you may need to think again.
Two of our biggest climate drivers are weaker than usual. And what will be good news for farmers, that might just give a few more downpours a chance to squeeze in over the coming months. But they will be accompanied by scorching heat.
The season officially ticks over on Saturday and the Bureau of Meteorology has issued its outlook for the summer months. It comes as the El Nino climate driver waits in the wings, ready to make an imminent entrance.
“Summer is looking drier than average across the north and warmer than average for most of the country,” said Dr Andrew Watkins, the Bureau’s manager of long-range forecasting.
But in the south there is still a 50/50 chance of a season of average rainfall. And states like New South Wales and Victoria need it with parched earth and low dam levels, despite recent torrential downpours.
“The drought continues even though El Nino is not locked in. Inflows into water storages are far lower than at this time last year,” Dr Watkins said.
“Storages in the northern Murray Darling basin are down to 17 per cent and Sydney’s main water storage, the Warragamba Dam, dropped almost a quarter of its capacity and is at the lowest levels since the end of the millennium drought.”
The Warragamba Dam has recovered slightly since Wednesday’s record breaking torrential downpours to 63.9 per cent. But this is still far below the 85.7 per cent 12 months ago.
SCORCHING SPRING
“It was Australia’s driest September on record but some places had heavy rainfall in October and November thanks to tropical moisture and spring thunderstorms,” Dr Watkins said.
Birdsville’s high of 44.7C on 25 October was the highest temperature recorded that early in Spring. Just this week, Cairns Airport recorded its hottest ever temperature of 42.6C, although it was smidgen hotter down the road at the post office in 1923.
Dr Watkins said all indications were pointing towards Spring 2018 as having been one of the 10 warmest on record for the country as a whole.
One of the reasons behind the big dry has been the Indian Ocean Dipole (IOD), one of the two big climate drivers of Australia’s weather. When it’s in positive mode — as now — it can contribute towards drier conditions in the south east.
EL NINO, WHERE ART THOU?
Looking ahead, Dr Watkins said it was likely the IOD would soon decay. At the same time, with Pacific seas surface temperatures rising there was every indication the main Pacific climate driver, the ENSO, would head into positive territory and become an El Nino. But so far, it hadn’t had its usual effect of drying the southern states.
“The atmosphere yet to fully respond (to the positive ENSO) so until cloud, wind and pressure patterns reinforce those in the oceans the event is not locked in. As a result our ENSO outlook remains at El Nino alert,” he said.
Even if El Nino does make an appearance, its power to suck moisture from southern Australia is generally diminished during the summer months.
This weakness from both the IOD and El Nino was letting other factors in on the weather action.
“In the southern Tasman Sea high air pressure is likely to drive more humid air inland than normal and this has reduced the chance of dry conditions in south east Australia,” Dr Watkins said.
That doesn’t mean it’s definitely going to be wetter, just there’s now a fair chance of a rainy summer.
“Locally heavy rainfall events similar to what we have seen in NSW in the last two days are always a possibility during summer, no matter what the outlook is showing,” he said.
SCORCHING SUMMER
Wherever you are, it’s going to be hot though with an 80 per cent chance of warmer than average days and nights all the way through to at least February.
“We’ve already seen extremely hot temperatures through parts of north and central Queensland in recent days and this should act as an important reminder of the kinds of conditions we can get during an Australian summer.”
That doesn’t bode well for bushfire season.
So if you’re in Sydney, Melbourne, Canberra, Adelaide, Hobart and everywhere in between, fish out the beach towel by all means. But maybe keep the umbrella close by too.
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