Click here to load reader · Web view Jamestown increased by 33 per cent, up from 56 to 89 per cent and Waikerie increased by 28 per cent up from 22 to 50 per cent. Ruddal and Kimba both decreased,

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Text of · Web view Jamestown increased by 33 per cent, up from 56 to 89 per cent and...

The Fast Break Newsletter 27 May 2020

Seasonal climate risk information for South Australia

Volume 3 | Issue 5 |27 May 2020

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We are describing the cropping areas of South Australia broadly as south of a line starting at Ceduna to Pt Augusta and down to Renmark. Uses of the term’s east and west in this region refer to Port Augusta as a reference, or north and south of Adelaide. Local regions will be used if the models are more specific.

Apart from the south east, it has been drier than average in May. There haven’t been many rainy breaks to disrupt the sowing program, but some young crops would welcome a top up.

Much of the EP, except the far south is rated as normal for soil moisture. The rest of the state is generally wetter. Particularly the Upper North and the southern Riverland which is rated at decile 10 for soil moisture. Its early days for season 2020 and only a few sites are 100 per cent full already. Much of the EP in particular has spare capacity to hold more.

The Pacific Ocean made further inroads to looking pre-La Niña like with its pretty blue wiggle along the Equator. The surface cooled substantially due to enhanced trade wind activity in the central Pacific. Cloud patterns at the dateline are also indicative of La Niña, but as is often the case, it’s the pressure patterns not playing ball. The pressure at Darwin is still higher than Tahiti rather than being lower. The system will remain uncoupled if the SOI doesn’t go strongly positive.

The whole Indian Ocean remains warm but did cool off somewhat this month. Things are still very warm off the coast of Africa and until this changes, there will be no -IOD. Winds have picked up blowing from the west into Sumatra which would be needed to continue to kick a -IOD event off. Cloud has also increased over Indonesia for the first time in six months.

The Southern Annular Mode (SAM) had been negative but has recently gone moderately positive.

Pressure patterns whilst in a favourable position, being further north, were set up as a moisture blocking pattern to our north west. This meant just the fronts sneaking through the South East of SA.

My assessment of 12 climate models for South Australia shows a strong consensus for likely wetter rainfall and likely cooler temperatures for the next three months.

Soil Moisture

File - soil moist SA.png

Alt text- map of SA showing soil moisture probes measurements.

Caption – The BoM Australian Water Resources Assessment (AWRA) modelled plant available soil moisture (10-100cm) shows that the northern EP and the western half of KI are rated normal. The rest of SA’s cropping regions are rated as wetter. The soil moisture probes (courtesy of NR-SAMDB, EPARF, SARDI, AgByte and MFMG) show improvements of greater than 10% in yellow. Jamestown increased by 33 per cent, up from 56 to 89 per cent and Waikerie increased by 28 per cent up from 22 to 50 per cent. Ruddal and Kimba both decreased, by 10 and 15 per cent respectively. Ruddal from 44 down to 34 and Kimba from 44 down to 30 per cent.

Model distribution summary for the next three months

File - 1-3 month SA.png

Alt text - Graphs showing the distribution of global model forecasts for June-August, with a consensus of models leaning towards likely wetter and likely cooler temperatures.

Model distribution summary for the next four to six months

File- 4-6 month SA.png

Alt text - Graphs showing the distribution of global model forecasts for September-November, with models leaning towards likely wetter rainfall and split between likely cooler and neutral temperatures.

Model consensus forecast for the next six months

Current outlook (to 27 May)

Current outlook (to 27 April)





Pacific Ocean

Slightly cool

Cool (possible La Niña)


Cool (La Niña)

Indian Ocean

Warm (-IOD)

Warm (-IOD)

Slightly warm

Warm (-IOD)


Slightly wetter


Slightly wetter/ neutral

slightly wetter/ neutral


Slightly wetter


Neutral/slightly cooler


Sea Surface Temperature Anomalies

File - SSTa.png

Alt text - Equatorial Pacific Ocean Sea surface temperatures and the IOD are at neutral levels, oceans are warm to our north east and north west.

Caption – Sea surface temperature (SST) anomalies along the Equatorial Pacific cooled significantly this month but are still at normal temperatures. NINO3 is at -0.21oC and NINO3.4 is -0.28oC (as of 25 May). A La Niña would be when NINO3.4 got below -0.8oC. Oceans are still warmer to the north-west and north-east, an enhanced moisture source. The Dipole Mode Index is +0.31oC (as of 25 May), which is neutral. Positivity is being driven by the warm African box, but encouragingly the NE corner of this western IOD region cooled this month. Admittedly there is a lot of cooling that needs to occur in that region before anything reminiscent of a -IOD. The threshold for IOD events is +/- 0.4oC.

Equatorial Pacific Sub-Sea Temperature Anomalies

File - Deep sea a.png

Alt text - Equatorial undersea temperature anomalies in the Pacific have further cooled in May, showing a pre La Niña like pattern with upwelling at the surface.

Caption - The Pacific Ocean Equatorial sub-surface temperature anomalies have cooled further during May. Upwelling in the eastern Pacific is now occurring and is visible as the wavy blue region in the SST anomaly map. Such behaviour is consistent with developing La Niña’s, but it doesn’t guarantee they happen.

Southern Oscillation Index

File - SOI.png

Alt text - The SOI value is currently at +1.5 (as at 25 May).

The SOI spent most of May in neutral territory, currently at +1.5 (as at 25 May). More convincing evidence for a La Niña would be a significantly positive SOI. This would be when pressure is lower at Darwin and higher at Tahiti, with a sustained SOI value above +7. Until the pressure patterns and the ocean surface are reinforcing each other, the system will be uncoupled.

Pacific Ocean Surface Wind Anomalies

File - trade winds.png

Alt text - The Equatorial trade winds are stronger in the western/central Pacific. The trade winds are stronger westerly off Sumatra.

Caption –Trade Winds have been blowing slightly stronger in the central Pacific helping to upwell the cooler water at depth. This would need to keep going, to cool off the Pacific further. From the SST anomaly chart it can be seen that the stronger Trade winds have pushed warmer water around PNG. In the Equatorial Indian Ocean, winds were normal in the middle of the month, but have recently started blowing stronger westerly towards Sumatra. This positioning is more in keeping with a -IOD and would be needed to continue for that to occur.

World Cloudiness Anomalies

File - OLR.jpg

Alt text - Cloud is decreased at the Dateline and normal to the north of Australia. Greater cloud is off Sumatra.

Caption - Cloud at the International Dateline (180oW) junction with the Equator is reduced, this is more in keeping with La Niña (brown colour). A more convincing La Niña pattern would be if the cloud anomaly was more centred over the Equator. For the last six months cloud over Indonesia and north of Australia has been less. A welcome change to this pattern has finally occurred with greater cloud off Sumatra and normal to greater cloud in the Arafura Sea. The north west cloud band pattern visible last month has disappeared.

Southern Annular Mode

File- SAM.png

Alt text- the SAM spent May split between weakly negative and moderately positive.

The Southern Annular Mode (SAM) or Antarctic Oscillation (AAO) spent May split between weakly negative and moderately positive. A positive SAM means the westerly winds around Antarctica have sped up and are pulling fronts further south of Australia. SAM would traditionally have a greater impact on SE SA during winter. The NOAA 14 day prediction for SAM is trending towards staying weakly to moderately positive.

Air Pressure

File - STR posn.png

Alt text - The STR of high pressure is in a winter position centred over the Bight.

Caption - In the past 30 days, the Sub Tropical Ridge of High Pressure (STR) has been positioned at a normal winter position over the Bight, some two months earlier than normal. This would have suggested that frontal systems were able to come closer to SA. While rainfall has been erratic in May, temperatures have been toned down by the persistent cool south westerly winds.

Air Pressure Anomalies

File - STR strength.png

Alt text - Pressure is slightly higher at Darwin and at Tahiti, the SOI is neutral. A large high has been over Western Australia

Caption - The Sub Tropical Ridge of High Pressure was higher in pressure over SA, due to a large high over Western Australia. This was curtailing the north west cloud band activity of the previous month. The pressure is slightly higher at Darwin and at Tahiti which is why the SOI is normal. More convincing La Niña pressure patterns would see the pressure drop at Darwin.

Modelled Climate and Ocean Predictions for South Australia from May 2020 run models

Ocean-Atmosphere Coupled Models

Multi Model Ensembles


System 5