Wet­tish weather

It’s a mixed bag as we move to­wards a weak La Niña

Farms & Farm Machinery - - Contents -

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

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