Seasonal climate risk information for Southern NSW
Volume 2 | Issue 1 | 12 February 2020
Welcome to the “Fast Break” newsletter for the Southern New South Wales grains industry. We have been constructing these summaries for the last 11 years in Victoria, and started last year in South Australia, New South Wales and Tasmania as part of the GRDC funded “Using Seasonal Forecasts Project” project. If you like it, 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.
The +IOD and the -SAM that conspired to give eastern Australia very dry and hot weather in December both died around new year. The northern wet season which had been inhibited by these drivers at that time was then able to kick off. Since then, summer weather has been a bit erratic.
At the moment, both the El Nino Southern Oscillation and the Indian Ocean Dipole are in neutral phases as is normal for now. We reach the dodgy time of the year where random things can happen to push them in a direction for winter, with limited predictability. Ocean temperatures to our north are generally much warmer, which instigates greater evaporation. Models agree that the Indian and Pacific Oceans are likely to stay warmer for the next three months to the north of Australia.
We currently have enhanced cloud formation over the Coral Sea to the north-east of Australia. This is providing a good moisture source but only if the right triggers drift past. Decreased cloud to our north and increased pressure, are a hang-over from mid-January, where more recent measurements of cloud at least, are closer to normal. The higher pressure north of Darwin is normally not a good omen for moisture transport and probably not helping the western regions.
The Southern Annular Mode is now behaving itself, bouncing around from weakly positive to weakly negative. This would be expected to have little influence on NSW’s climate.
Pressure has been lower due to the positioning of large stable highs to our west and east. If this pattern continues, we could expect some more humid and unstable weather.
For the next three months models are firmly sitting on the fence for any outcome is possible, drier, average or wetter, but there are sniffs of drier from a few. There is a strong consensus for warmer temperatures.
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The BoM Australian Water Resources Assessment (AWRA) modelled soil moisture shows the Riverina has not enjoyed the rainfall that areas further north have received. The Central West has had the best recent falls of up to 100mm and increasing stored moisture. That region is currently rated very much above average.
Model distribution summary for the next three months
Model distribution summary for the next four to six months
Model consensus forecast for the next six months
Current outlook (to 11 February)
Previous outlook (to 28 November)
Slightly warmer/ slightly cooler
Average/ slightly drier
Sea surface temperature anomalies
The +IOD finally broke down in the first week of January which was historically very late. Current values of the Dipole Mode Index are -0.06oC (as of 11 February) which are totally neutral. This is to be expected for this time of the year. Sea surface temperature (SST) anomalies along the Equatorial Pacific have slightly cooled over summer to remain at neutral temperatures. NINO3 is at +0.11oC and NINO3.4 is +0.24oC (as of 11 February). The Coral, Arafura and Timor Seas to our north are warmer than normal and evaporating more moisture. If the right trigger can be received summer rainfall is possible.
Equatorial pacific sub-sea temperature anomalies
The Pacific Ocean Equatorial sub-surface temperatures anomalies have changed little over the last three months. A warm patch exists below the western Pacific, which could be vulnerable to reversed trade winds pushing it under and over to South America.
Southern oscillation index
The SOI has been in neutral territory for the last three months. The value is currently neutral at +0.1 (as at 11 February). In summer, the SOI is a less reliable indicator, due to large swings in local pressure at Darwin and Tahiti when cyclones occur.The SOI has been in neutral territory for the last three months. The value is currently neutral at +0.1 (as at 11 February). In summer, the SOI is a less reliable indicator, due to large swings in local pressure at Darwin and Tahiti when cyclones occur.
Pacific ocean surface wind anomalies
The Equatorial Pacific Easterly Trade Winds have shown stronger easterly behaviour in the Central Pacific. Paradoxically there is some reversal to westerly off Papua New Guinea. The convergence of these two is causing greater cloud formation.
World cloudiness anomalies
Cloud at the International Dateline (180oW) junction with the Equator is much greater (blue colour) which is suggestive of El Niño, but the projection of greater cloud further west into the Coral Sea is not in keeping with El Niño. The lack of cloud (brown colour) over Indonesia still shows some hang over from the +IOD pattern of last year. Greater cloud over eastern Australia has been from moisture streaming in from the warm Coral Sea
Southern annular mode
The Southern Annular Mode (SAM) or Antarctic Oscillation (AAO) was negative into December but has remained close to normal during January and into February. In summer a negative SAM would classically cause drying along the eastern half of NSW. The finger can be pointed at SAM for aiding the dry spring and early summer. NOAA predicts that for the next 14 days the SAM will have a small negative burst. Once we reach autumn SAM has a variable effect on our climate.
In the past 30 days, the Sub Tropical Ridge of High Pressure (STR) has been slightly north of the normal summer position of Melbourne. This has been inhibiting the tropical air from getting to the western regions. We have been situated between two high pressure systems which has been moderating the extremes of climate. There has been more troughing of moisture from the north.
Air pressure anomalies
The Sub Tropical Ridge of High Pressure has been lower over SE Australia, indicating more opportunity for rainfall and unstable weather. The position of low pressure put the western region in the drier zone. Pressure at Darwin and Tahiti is slightly higher which is why the SOI is neutral. Slightly higher pressure to our tropical north is linked to the lack of cloud in that region too.
Modelled Climate and Ocean Predictions for Southern NSW from January 2020 run models
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