The Fast Break Newsletter 26 June 2020Seasonal climate risk information for Southern NSW

Volume 2 | Issue 6 |26 June 2020

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We are describing SNSW as a line south of Dubbo. In the predictions, I divide this region into quarters, hence N, S, E, W, NW, NE, SW, SE, defines zones in this southern half. If the models are more precise, I might use terms such as coast, Riverina, Central West, etc.

Some higher rainfalls in the north and far south of SNSW have seen increases to soil moisture but in most areas, rainfall has kept up with crop use with small to no increases. The Mallee and western Riverina has plenty of spare moisture 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 southern Victoria. Historically SAM has had an erratic effect on SNSW in winter. 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 SNSW 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 SNSW shows a consensus for wetter rainfall and neutral temperatures for the next three months.

Soil Moisture

File - soil moisture SNSW.pngAlt text - map of Southern NSW showing plant available moisture (%).Caption – The BoM Australian Water Resources Assessment (AWRA) modelled plant available soil moisture shows modest increases for the month in the Central West and the southern Riverina. Most other regions were stable. Profiles are modelled to be half full or lower in most places. The Riverina is on the lower end, with plenty of spare capacity. This month’s decile ranking has decreased for many areas, with the Riverina and west of the Newell Hwy now ranked normal, and the slopes at decile eight to nine. Only a region around Forbes remains at decile 10. The Mallee has now dropped to decile two to three.

Model distribution summary for the next three months

File - 1-3 month SNSW.pngAlt text - Graphs showing the distribution of 12 global model forecasts for July-September, with consensus for wetter rainfall and a neutral temperature forecast.

Model distribution summary for the next four to six months

File - 4-6 month SNSW.pngAlt text - Graphs showing the distribution of nine global model forecasts for October-December, with

consensus for wetter rainfall and a neutral temperature forecast.

Model consensus forecast for the next six months

Current outlook (to 25 June) Previous outlook (to 25 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 Slightly wetter

Temperature Slightly wetter Neutral Neutral/ slightly cooler Slightly 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.png

Alt 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.pngAlt 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. 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. To counter this the large high pressure over southern Australia has put SNSW over a dead zone, just to the west of the pressure centre.Air Pressure Anomalies

File - STR strength.pngAlt text - Pressure was higher over SNSW in June. Pressure is higher at Darwin and normal at Tahiti.Caption - The Sub Tropical Ridge of High Pressure was higher over SNSW in June. This would mean slower moving high-pressure systems chasing fronts away. Pressure has its greatest effects in winter over SNSW. 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 Southern NSW 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 JAS

Rainfall Skill JJA Moderate Moderate - Moderate Low/Moderate Moderate - Moderate Moderate - - -

Winter Pacific Ocean NINO3.4

Slightly cool (weak La Niña)

Slightlycool

Slightlycool

Slightlycool

Cool(Weak La

Niña)Slightly

coolSlightly

cool Slightly

coolCool

(Weak La Niña)

Slightlycool

Cool(Weak La Niña) SOI falling

Winter EasternIndian Ocean

Slightlywarm

Slightlywarm

Normal(+IOD)

Warm(weak -IOD)

Slightly warm (weak -IOD)

Slightlywarm

Warm(weak -IOD)

Slightlywarm

Warm(weak -IOD)

Warm(weak -IOD)

Warm(weak -IOD) -

Winter Rainfall Slightlywetter

Slightlywetter Neutral Slightly wetter

N, neutral SNeutral W,

slightly wetter E

Slightly wetter

Slightlywetter

Slightly wetter

Slightly wetter,

neutral far NW

Slightly wetter

Slightlywetter Neutral

Winter Temperature Neutral Slightlywarmer Neutral

Neutral E, slightly cooler

WNeutral

Neutral, slightly

cooler NE

Neutral W, slightly cooler

E

Neutral, slightly

warmer NW

Slightly cooler, neutral Slopes

Neutral, slightly

cooler SWNeutral -

Forecast months OND OND SON OND OND - SON SON OND SON OND -

Spring Pacific Ocean NINO3.4

Slightly cool (weak La Niña) Slightly cool Slightly cool Cool

(weak La Niña)Cool

(La Niña) - NormalSlightly cool

(weak La Niña)

Slightly cool (weak La

Niña)Slightly cool Slightly

cool -

Spring EasternIndian Ocean

Warm(-IOD)

Slightlywarm Normal Warm Warm

(-IOD) - Slightlywarm

Warm(weak -IOD)

Slightlywarm

Warm(-IOD)

Slightlywarm -

Spring Rainfall Slightly wetter W, neutral E - Neutral Slightly wetter

Slightly wetter W, neutral E

- Slightly wetter S, neutral N Wetter

Slightly wetter,

neutral far WSlightly wetter

Slightlywetter -

Spring TemperatureNeutral E,

slightly warmer W

- Slightlywarmer Slightly cooler

Neutral, slightly

cooler Slopes-

Slightly warmer, neutral

coast

Neutral W, slightly

warmer E

Slightly cooler,

neutral coast

Slightly cooler,

neutral coastNeutral, slightly cooler Slopes -

Notes Operational Operational Experimental Operational Experimental Experimental Operational OperationalExperimentalSummary of 4

dynamic models

ExperimentalSummary of 6

dynamic models

ExperimentalSummary of 8 dynamic

models

5 phase system based on previous 2

months SOI

File- big table SNSW.jpg

Alt text- 12 climate models show their predictions for the next six months for the Pacific Ocean, Indian Ocean, rainfall and temperature for SNSW