Fast Break: Season climate risk information for South Australia

Volume 1 | Issue 2

Welcome to the second “Fast Break” newsletter aimed at the South Australian grains industry. Our team has been preparing this monthly newsletter for more than 12 years in Victoria and with GRDC funding we are now able to present it for South Australians. If you like it, please consider passing it on through your networks so that others may subscribe.

The Pacific and Indian Oceans are still neutral, but local weather patterns consisting of very high pressure systems over Australia, are resulting in a continuation of the drier weather over the vast majority of South Australia.

Cloud patterns at the Dateline are still La Niña like, but other indicators (trade winds, SOI and surface temperatures) are normal. Surface heat under the Pacific increased during May, but didn’t track much further east.

The SAM is also neutral, meaning frontal systems are in a normal position spinning around Antarctica.
What isn’t normal is the blocking high over the Bight, chasing fronts and lows away and, of such strength, that its movement eastward is painfully slowly.

This large high is also having an impact on the water temperature in the Timor Sea, where stronger easterly winds are stirring the surface up and making it cooler. Cloud patterns off Sumatra are also not ideal.

All these things are hopefully temporary, but until they change, dry conditions seem likely.

Current predictions for the Pacific and Indian Oceans are all over the shop, but mainly sitting around neutral. A couple more models jumped on the El Niño train this month, and a few models got off the -IOD bandwagon.

Most models are still sitting on the fence with average rainfall for winter and spring, with warmer to average temperatures. Remembering that an average forecast in this context means an equal chance of above or below average rainfall.

If you would like more explanation of the contents of this newsletter, why not join our webinar for South Australia on 19 June. Follow this link for details.

Soil Moisture

map of Tasmania showing dry soil to depth but moisture probes showing higher values
The BoM AWRA modelled soil moisture map plant available soil moisture (10-100cm) is higher in the South East, the Mt Lofty Ranges and western Kangaroo Island. The rest of the state is dry to depth. The modelled soil moisture presumes pastures (weeds) have been using available water over summer, as opposed to croppers spraying out summer fallows to retain moisture. A selection of moisture probes (courtesy of EPARF, SARDI and Agbyte) shows generally high moisture levels, but it’s highly variable (30-100cm). The Pt Kenny, Warramboo, Pinkawillinie, Kimba, Rudall, and Ungarra probes have unfortunately dried significantly this month. The Parndana probe has been the only fortunate one to wet up. Other probes have had little change.

Model distribution summary for the next three months

Graphs showing the distribution of June-August modelled rainfall as average, and temperature as warmer to average.
Distribution of June-August modelled rainfall as average, and temperature as warmer to average.

Model distribution summary for the next four to six months

graphs showing the distribution of September-November modelled rainfall and temperature is for average
Distribution of September-November modelled rainfall and temperature is for average

Model consensus forecast for the next six months

Current outlook (28 May)

Previous outlook (28 April)

Jun-Aug outlook

Sept-Nov outlook

Jun-Aug outlook

Sept-Nov outlook

Pacific Ocean

Neutral

Neutral (possible El Niño)

Neutral

Neutral

Indian Ocean

Neutral

Neutral

Slightly warmer/neutral

Slightly warmer/neutral

Rainfall

Average

Average

Average

Average

Temperature

Slightly warmer/average

Average

Average

Average

Equatorial Pacific and Indian Ocean Sea surface temperature anomalies are normal. Seas to the north of Australia have cooled
Sea surface temperatures (SST) along the Equatorial Pacific have warmed a little further in the last month. NINO3 is at +0.21oC and NINO3.4 is +0.15oC (as of 28 May), both now slightly warmer, but neutral ENSO temperatures. The Coral Sea is hanging in warmer, as is the central Indian Ocean. Temperatures in the Timor Sea have cooled rapidly as the result of stronger than normal easterly winds resulting from the large high pressure in the Bight. Time will tell whether this is permanent or an aberration that changes if the large highs disappear. Underlying warmer ocean at depth in this region would suggest a return to normal.
Undersea warm temperatures have increased in the central Pacific but haven’t progressed far eastwards.
The Pacific Ocean Equatorial sub surface temperatures warmed further at depth, without any major eastwards progression. The models which are predicting an El Niño must be getting the majority of the signal from here. For an El Niño to happen trade winds would need to reverse and the SOI go negative. With the current position of the heat, an El Niño would be unlikely to occur until spring, if at all.
The SOI value is currently at +0.3 and rising
The SOI is currently close to zero at +0.3 (as of 28 May). Pressure patterns around the Equator as measured at Darwin and Tahiti are both higher which is somewhat different from them being both normal. The northern wet season is over and values of the SOI are more meaningful now that tropical pressure can’t be mucked around by tropical weather.
The Equatorial Pacific trade winds have been normal throughout May. Equatorial Pacific trade winds. Anomalies: Five-day mean ending on may 26 2018.
The Equatorial Pacific easterly Trade Winds were again normal through May (shown by the small or non-existent arrows). This has led to the slow re-warming of sea surface temperatures across this region. In coming months watch for reversed trade winds (westerlies) around PNG (El Niño), or stronger easterlies in the central Pacific (La Niña), or just normal trade winds (neutral).
there has been less cloud at the junction of the Equator with the Dateline, which is consistent with La Nina and there has been less cloud off Sumatra which is more like a +IOD.
Cloud at the International Dateline (180oW) junction with the Equator has been less (brown colour) in the last 30 days. Still a La Niña like cloud pattern but the only evidence anywhere of one. The cloud to the north of Australia became more normal but the cloud off Indonesia is more reminiscent of a weak +IOD.
the SAM has spent May behaving normally.
The Southern Annular Mode (SAM) has done nothing during May and Kangaroo Island has been wetter than normal. We are only just approaching the winter period where SAM has its greatest influence over frontal system positioning in southern regions. The BoM and NOAA models suggest a quick dip into negativity and a return to neutral in coming weeks.
the STR of high pressure has been at a winter position at the top of the Bight.
In the past 30 days, the Sub Tropical Ridge of High Pressure has been in a slightly better position centred just south of the Bight. This could be expected to be letting frontal systems through. The problem is the position over the Bight, leading to a classic blocking pattern for SE Australia. Until this shifts, good rainfall seems unlikely.
pressure at Darwin and Tahiti are both higher, where pressure over SE Australia has been much higher.
The Sub Tropical Ridge of High Pressure was much higher in pressure over SE Australia. This meant the highs moved very slowly, keeping them in the blocking position and effectively forcing fronts and lows further south. In past memory, this is a classic dry pattern if it occurred in winter. Pressure at Darwin and Tahiti are both higher which is why the SOI is neutral. The high pressure at Darwin is as a result of the large high and not a wholesale change to the world’s Equatorial pressure patterns.

Modelled Climate and Ocean Predictions for South Australia from May 2018 run models

To view the table below, please download the word document with the table contained inside.

12 climate models show their predictions for the next six months for the Pacific Ocean, Indian Ocean, rainfall and Temperature for South Australia.