The Fast Break Newsletter 27 May 2020 Seasonal climate risk information for Southern NSW Volume 2 | Issue 5 |27 May 2020 If you like the publication, please consider passing it on through your networks and subscribing. 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. It has been drier in May, but few people are complaining, as it’s allowed timely sowing of crops across the region and into perfect moisture. Most of SNSW’s soil moisture is now ranked as wetter than normal. 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. Pressure patterns whilst in a favourable position, being further north, were set up as a moisture blocking pattern to the north west, probably the main reason for the drier month. My assessment of 12 climate models for SNSW shows a strong consensus for likely wetter rainfall and a split between likely neutral or cooler temperatures for the next three months. Soil Moisture
Transcript
The Fast Break Newsletter 27 May 2020Seasonal climate risk information for Southern NSW
Volume 2 | Issue 5 |27 May 2020
If you like the publication, please consider passing it on through your networks and subscribing.
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.
It has been drier in May, but few people are complaining, as it’s allowed timely sowing of crops across the region and into perfect moisture. Most of SNSW’s soil moisture is now ranked as wetter than normal.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.Pressure patterns whilst in a favourable position, being further north, were set up as a moisture blocking pattern to the north west, probably the main reason for the drier month.My assessment of 12 climate models for SNSW shows a strong consensus for likely wetter rainfall and a split between likely neutral or cooler 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 soil moisture shows increases for the month and much of the SNSW cropping region is ranked as wetter than normal. The central Newell Highway is ranked at decile 10. The Riverina still has spare capacity to hold moisture.
Model distribution summary for the next three months
File - 1-3 month SNSW.pngAlt text - Graphs showing the distribution of global model forecasts for June-August, with models predicting higher chances of wetter rainfall, with a split between neutral and cooler temperatures.
Model distribution summary for the next four to six months
File - 4-6 month SNSW.pngAlt text - Graphs showing the distribution of global model forecasts for September-November, with models predicting higher chances of wetter rainfall and cooler temperatures.
Model consensus forecast for the next six months
Current outlook (to 27 May) Current outlook (to 27 April)Jun-Aug Sep-Nov May-Jul Aug-Oct
Pacific Ocean Slightly cool Cool (possible La Niña)
Normal Cool (La Niña)
Indian Ocean Warm (-IOD) Warm (-IOD) Slightly warm Warm (-IOD)Rainfall Slightly wetter Slightly wetter Slightly wetter Slightly wetter
Temperature Neutral/ slightly cooler Slightly cooler Neutral Neutral
Sea Surface Temperature Anomalies
File - SSTa.pngAlt 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.pngAlt 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.pngAlt 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.pngAlt 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.jpgAlt 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. Cloud was normal over SNSW.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 not have a great impact on SNSW during winter. The NOAA 14-day prediction for SAM is trending towards staying weakly to moderately positive.Air Pressure
File - STR posn.pngAlt 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 suggest that frontal systems were able to come closer to SNSW. While rainfall has been erratic in May, temperatures have been moderated by the persistent cool south westerly winds.Air Pressure Anomalies
File - STR strength.pngAlt text - Pressure is slightly higher at Darwin and at Tahiti, the SOI is neutral. A large high as been over Western AustraliaCaption - The Sub Tropical Ridge of High Pressure was normal in pressure over SNSW, but a large high over Western Australia curtailed the north west cloud band activity of the previous month. This has probably been the reason for the drier 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 Southern NSW from May 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 May May May May May May May May May May May May
File- big table SNSW.jpgAlt text- 12 climate models show their predictions for the next six months for the Pacific Ocean, Indian Ocean, rainfall and temperature for SNSW
