The Fast Break - Victoria

Seasonal climate risk information for Victoria

Volume 15 | Issue 7 | 29 July 2019

Soil moisture

The BoM Australian Water Resources Assessment (AWRA) modelled plant available soil moisture shows the higher rainfall areas with filling soil profiles. The northern Mallee and central Gippsland are drier.

Most of the north west and north central probes as well as central Gippsland have not moved significantly for the month at 30cm, with rainfall being too light to reach that depth. South west and north east probes continue to get wetter.

Model distribution summary for the next three months

Graphs showing the distribution of global model forecasts for August-October, with models leaning towards drier rainfall and no strong signal for temperatures.

Model distribution summary for the next four to six months

Graphs showing the distribution of November to January forecasts with models leaning towards average/slightly drier rainfall and average to warmer temperatures.

Model consensus forecast for the next six months

Sea Surface Temperature Anomalies

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Sea surface temperatures (SST) anomalies along the Equatorial Pacific have cooled a little bit further over July and remain at neutral temperatures. NINO3 is at +0.28°C and NINO3.4 is +0.49°C (as of 29 July), the threshold for an El Niño is +0.8°C.

The anomalies compare the current temperature to the average temperature over the last 25 years on this date. Cooler waviness in the eastern Equatorial Pacific is because of the cooler water at depth upwelling from the easterly Trade Winds.

The Dipole Mode Index (DMI) shows a neutral IOD at +0.18 (as of 29 July), the threshold for +IOD is +0.4°C.

Despite the cooling off Sumatra not quite being in the right spot, with a Javan style +IOD and some normality to the West African temperatures, the wind and cloud patterns are in keeping with a classic +IOD event.

Equatorial Pacific Sub-Sea Temperature Anomalies

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The Pacific Ocean Equatorial sub-surface temperatures have done very little during July.

A cooler anomaly in the east is starting to upwell at the surface, but the warmth in the central Pacific is negligible compared to a classic El Niño.

Southern Oscillation Index

The SOI value is currently at -7.8 (as at 29 July) and spent all of July at a significantly El Niño level of negativity (El Niño SOI level kicks in at negative 8 and beyond).

This suggests pressure patterns around the Equator are weakly El Niño like, but the main driver is still the increased pressure at Darwin. Regardless, the Pacific Ocean is not remotely interested in El Niño.

Pacific Ocean Surface Wind Anomalies

The Equatorial Pacific Easterly Trade Winds had some westerly reversed activity for 12 days of July but this doesn’t seem to have had any effect on the Pacific surface or the undersea. Now the Trade Winds are behaving normally.

World cloudiness anomalies

Cloud at the International Dateline (180^oW) junction with the Equator is normal (white colour) suggesting there is no El Niño in play.

The lack of cloud (brown colours) off Indonesia and the greater cloud off Africa (blue colours) is a classic +IOD pattern. There has been a lack of cloud over SE Australia.

Southern Annular Mode

The Southern Annular Mode (SAM) or Antarctic Oscillation (AAO) started positive but flipped into moderate negativity for half the month.

A negative SAM means a weakening of westerly winds around Antarctica and a pushing of frontal systems and storm tracks closer to southern Victoria.Winter is when the SAM has its greatest influence.

Air pressure

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This has been letting frequent fronts through, particularly in southern areas. The higher than normal pressure has been putting stronger than normal easterly winds around Indonesia helping to upwell the cooler water in that region.

Air pressure anomalies

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The Sub Tropical Ridge of High Pressure was stronger than normal over the whole of the mainland, but absolute pressure has backed off from the highs in June.

Higher pressure at Darwin makes it harder to get moisture down to southern areas. Higher pressure at Darwin and normal pressure at Tahiti is why the SOI is negative.

Modelled climate and ocean predictions for Victoria from July 2019 run models

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12 climate models show their predictions for the next six months for the Pacific Ocean, Indian Ocean, rainfall and temperature for Victoria.

The Fast Break is produced by Agriculture Victoria as part of the GRDC's (Southern and Northern Region) Using Seasons Forecasts Partnership Project.