The Fast Break Newsletter 26 June 2020 Seasonal climate risk information for South Australia Volume 3 | Issue 6 |26 June 2020 If you like this publication, please consider passing it on through your networks and subscribing. 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. Soil moisture increased along southern coastal areas and parts of the Eyre Peninsula but remained unchanged across most other areas. Rainfall and plant water use were in balance, but many soils are only half full with spare capacity. In the Pacific Ocean, around a third of the models surveyed predict a weak “just at threshold” La Niña can form in coming months and why the BoM moved to La Niña watch. The eastern Pacific surface cooled further, but the central Pacific is unchanged, both slightly cooler but neutral. The amount of colder water to depth has reduced, particularly in the central Pacific. The atmosphere is where the success of this La Niña attempt lies. At the moment, only less cloud at the Dateline matches the ocean. It needs more support from the trade winds and the pressure patterns, as without those, it will struggle to form. The Indian Ocean is even more delicately poised. This region is worth watching intently in coming weeks and months. About half of the models surveyed are predicting a weak to moderate negative IOD in coming months. Major changes are needed off Africa for this to occur. In the last month there has been no change to the SST anomalies to our NW after they neutralised from warm to normal in May. Current ocean temperatures are much warmer off Africa and normal around Sumatra. This has caused the Dipole Mode Index to be at around the threshold for +IOD in recent weeks. Warmer water to depth, lower pressure and more cloud off Kenya is also more reminiscent of a +IOD. Fortunately, normal water at the surface and warmer at depth, normal pressure and cloud off Sumatra are not features of the eastern part of a positive dipole. Despite this, a
Transcript
The Fast Break Newsletter 26 June 2020
Seasonal climate risk information for South Australia
Volume 3 | Issue 6 |26 June 2020
If you like this publication, please consider passing it on through your networks and subscribing.
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.
Soil moisture increased along southern coastal areas and parts of the Eyre Peninsula but remained unchanged across most other areas. Rainfall and plant water use were in balance, but many soils are only half full with spare capacity.
In the Pacific Ocean, around a third of the models surveyed predict a weak “just at threshold” La Niña can form in coming months and why the BoM moved to La Niña watch. The eastern Pacific surface cooled further, but the central Pacific is unchanged, both slightly cooler but neutral. The amount of colder water to depth has reduced, particularly in the central Pacific. The atmosphere is where the success of this La Niña attempt lies. At the moment, only less cloud at the Dateline matches the ocean. It needs more support from the trade winds and the pressure patterns, as without those, it will struggle to form.
The Indian Ocean is even more delicately poised. This region is worth watching intently in coming weeks and months. About half of the models surveyed are predicting a weak to moderate negative IOD in coming months. Major changes are needed off Africa for this to occur. In the last month there has been no change to the SST anomalies to our NW after they neutralised from warm to normal in May. Current ocean temperatures are much warmer off Africa and normal around Sumatra. This has caused the Dipole Mode Index to be at around the threshold for +IOD in recent weeks. Warmer water to depth, lower pressure and more cloud off Kenya is also more reminiscent of a +IOD. Fortunately, normal water at the surface and warmer at depth, normal pressure and cloud off Sumatra are not features of the eastern part of a positive dipole. Despite this, a north west “lack of cloud” anomaly streaming across southern Australia is also more like a +IOD.
The Southern Annular Mode has been in a persistent moderate positive phase for June. This would be expected to pull fronts away from SE South Australia and the lower rainfall this month would suggest this has been at least partly to blame. The SAM is currently normal and models are mixed as to which direction it’s going to head in coming weeks.
Pressure patterns are a mixed bag, the absolute latitude of the sub-tropical ridge is at a helpful more northern winter position. The position of the high has seen SA on average in the dead zone, just to the west of the high’s centre. The other major problem has been higher than normal pressure all over the country, chasing fronts further south and not assisting moisture transport from the tropics.
My assessment of 12 climate models for South Australia shows a marked change from last month’s wetter forecasts, now showing a split between likely wetter and neutral rainfall and neutral temperatures. There is greater consensus for a wetter Eyre Peninsula.
Soil Moisture
File - soil moist SA.pngAlt text- map of SA showing soil moisture probes measurements. Some probes wet up this month, particularly along the coast, where most remained unchanged. The Pinnaroo probe was the only one to decrease.Caption – The BoM Australian Water Resources Assessment (AWRA) modelled plant available soil moisture (10-100cm) shows that profiles are slowly filling in the lower Eyre Peninsula, South East, Kangaroo Island, Adelaide Hills and Fleurieu Peninsula. Other areas show plenty of room in the profile. The soil moisture probes (courtesy of NR-SAMDB, EPARF, SARDI, AgByte and MFMG) show a number moved by greater than 10% this month on the EP and along the coast. Most other sites remained unchanged with rainfall matching water use. Lock increased from 52 per cent to 67 per cent and Rendelsham increased rapidly from around 50 per cent to 100 per cent. Pinnaroo decreased from 62 per cent to 52 per cent from crop water use.
Model distribution summary for the next three months
File - 1-3 month SA.pngAlt text - Graphs showing the distribution of 12 global model forecasts for July-September, with a split between likely wetter and neutral rainfall, with a neutral temperature forecast.
Model distribution summary for the next four to six months
File- 4-6 month SA.pngAlt text - Graphs showing the distribution of nine global model forecasts for October-December, with models split between likely wetter and neutral rainfall, with a neutral temperature forecast.
Model consensus forecast for the next six months
Current outlook (to 26 June) Previous outlook (to 27 May)Jul-Sep Oct-Dec Jun-Aug Sep-Nov
Pacific OceanSlightly cool (possible weak La Niña)
Slightly cool (possible weak La Niña)
Slightly cool Cool (possible La Niña)
Indian OceanSlightly warm (possible weak -IOD)
Warm (possible weak -IOD)
Warm (-IOD) Warm (-IOD)
Rainfall Slightly wetter/neutral
Slightly wetter/neutral Slightly wetter Cooler
Temperature Neutral Neutral Slightly wetter Neutral/cooler
Sea Surface Temperature Anomalies
File - SSTa.pngAlt text - Equatorial Pacific Ocean Sea surface temperature is slightly cool but neutral and the Indian Ocean Dipole is at weak positive values.Caption – Sea surface temperature (SST) anomalies along the Equatorial Pacific are cooler in the east, but unchanged in the centre this month and still at normal temperatures. NINO3 cooled most, to be at -0.55oC and NINO3.4 is unchanged at -0.20oC (as of 26 June). A La Niña would be when NINO3.4 got below -0.8oC. The western Indian Ocean remains very warm, and around Sumatra is normal. The Dipole Mode Index (DMI) is +0.4, at the threshold for +IOD. Other indicators in the west are +IOD like, but Indonesian indicators are not. The Indian Ocean is a long way from being in a negative IOD phase.Equatorial Pacific Sub-Sea Temperature Anomalies
File - Deep sea a.pngAlt text - Equatorial undersea temperature anomalies in the Pacific have warmed to normal in the central Pacific but remain cooler in the eastern Pacific.Caption - The Pacific Ocean Equatorial sub-surface temperature anomalies have warmed to more normal levels during June in the central Pacific. The Eastern Pacific remains cooler to depth but has lost some coldness too. This would indicate a loss of enthusiasm for La Niña by the undersea.Southern Oscillation Index
File - SOI.pngAlt text - The SOI value is currently at -9.0 (as at 29 June).The SOI took a dive into negativity in June, currently at -9.0 (as at 29 June). This would indicate El Niño like pressure patterns around the Equator. Despite this no other ENSO indicator is in agreeance. The main reason for the negativity is the long remaining high pressure at Darwin, with no change to the pressure at Tahiti. The ocean and atmosphere are uncoupled.Pacific Ocean Surface Wind Anomalies
File - trade winds.png
Alt text - The Equatorial trade winds have been close to normal across the Pacific and Indian OceansCaption –Trade Winds have been normal in the Pacific Ocean. Some small stronger anomalies existed in the central Pacific, but not enough to change the underlying ocean situation. This lack of stronger easterly Trade Winds is why the attempted La Niña at the ocean surface is not getting any support. Most of the Indian Ocean has had normal winds. There has been a small stronger burst of south easterly wind near Java. this is not in keeping with a -IOD, as winds would normally be stronger westerly.World Cloudiness Anomalies
File - OLR.jpgAlt text - Cloud is lower at the Dateline consistent with La Niña. There has been less north west cloud band activity. There is a large amount of cloud off East Africa.Caption - Cloud at the International Dateline (180oW) junction with the Equator is less indicating La Niña like patterns. What is not La Niña like though, is the strong lack of cloud to the west of the Dateline, perplexingly over the top of warmer water. Cloud patterns finally resemble normality to the north of Australia, after 10 months of less cloud. A lack of north west cloud band activity is visible and like the increased activity in March and April, this is a much lower trajectory than normal cloud bands. There has been less cloud over SA. The large amounts of cloud over the warm water north of Madagascar are more in keeping with +IOD than -IOD.Southern Annular Mode
File- SAM.pngAlt text- the SAM has spent most of June in a moderate positive phase.The Southern Annular Mode (SAM) or Antarctic Oscillation (AAO) spent most of June in a moderate positive phase. SAM has its most influence over SE South Australia in winter and an erratic effect elsewhere. A positive SAM would usually mean frontal systems are pulled further away from mainland Australia. The SAM is currently slightly negative and models are mixed as to which direction it’s going to head in coming weeks.
Air Pressure
File - STR posn.pngAlt text - The STR of high pressure was at a winter position centred over the Bight, Caption - In the past 30 days, the Sub Tropical Ridge of High Pressure (STR) has been at a normal winter position centred over the Bight. This happened in late April many weeks earlier than normal. This has been a positive influence allowing fronts to come closer to southern Australia. The large high pressure over southern Australia has put most of SA in a dead zone of high pressure.Air Pressure Anomalies
File - STR strength.pngAlt text - Pressure was higher over SA in June. Pressure is higher at Darwin and normal at Tahiti.Caption - The Sub Tropical Ridge of High Pressure was higher over South Australia in June. This would mean slower moving high-pressure systems chasing fronts away. Pressure has its greatest effects in winter over SA. Pressure was higher at Darwin and normal at Tahiti which is why the SOI is negative. Pressure is higher to our north which is not ideal for moisture transport down. La Niña would normally see lower pressure at Darwin and a -IOD would see lower pressure at Sumatra. At the moment, pressure patterns are far from interested in these two phenomena.
Modelled Climate and Ocean Predictions for South Australia from June 2020 run models
Ocean-Atmosphere Coupled Models Multi Model Ensembles Statistical
System 5ECMWFEurope
ACCESS-SBoM
Australia
SINTEX-FJAMSTEC
Japan
CFSv2NCEPUSA
GEOS-S2SNASAUSA
EPSJMA
Japan
CSM1.1mBCCChina
GloSea5UKMO
UK
NMMEUSA
C3SEurope
MMEAPCCKorea
SOI phaseUSQ/QldAustralia
Month of Run June June June June June June May June June June June June
Forecast months JAS JAS JJA JAS JAS JAS JAS JAS JAS JAS JAS JASRainfall Skill MJJ
File- big table SA.pngAlt text- 12 climate models show their predictions for the next six months for the Pacific Ocean, Indian Ocean, rainfall and Temperature for South Australia.
