The Fast Break - Victoria
Seasonal climate risk information for Victoria
Volume 15 | Issue 6 | 28 June 2019
Adequate follow up rains occurred across most of the state in June with parts of the Wimmera and South West being wettest, while totals in the north have generally been lower than average.
The southern region’s break was later than desirable and pasture growth has not been ideal.
Growth in the north has been good. Areas of far NW Victoria, central Gippsland and highland catchments could do with greater rain.
The Bureau of Meteorology have recently moved their ENSO outlook to inactive. Over the last three months, insufficient atmospheric support for the warm water at the surface (from the trade winds mainly) has caused the ocean to lose interest in being El Niño.
The majority of models agree that a second coming of this event is unlikely this year.
The Indian Ocean is the region that everyone is looking at currently. Stronger easterly winds (because of the large highs over Australia) have stirred up cooler water to the NW of Australia.
Most models surveyed predict a positive Indian Ocean Dipole (+IOD) over winter easing by spring. Excessive heat has built up off the African Coast, but recently this shows some cooling trend.
There has been a classic +IOD like lack of cloud cover off Indonesian. Historically, +IOD’s lead to greater chances of a drier winter/spring in Victoria.
Pressure patterns have been favourable in terms of position, especially for southern Victoria allowing fronts through, but unfavourable in term of absolute pressure, i.e. moving slowly and also bringing the odd frost.
A few more models have shifted slightly drier, with the majority now leaning towards higher chances of a drier next three months, with temperature predictions strangely all over the shop.
The BoM AWRA modelled plant available soil moisture shows increases over Victoria, with percentage increases really depending on rainfall totals over the past month.
The NW and central Gippsland have not had the good start that other regions have had.
The Perennial Pasture Systems and Agriculture Victoria soil probe network shows 13 sites increased by 10% over the month with moisture detected at 30cm depth, while all other probes stayed the same or with a small increase.
There were slight decreases of less than 10% in the NW, probably due to evaporation. Probes at Werrimull, Ouyen, Speed, Normanville, Elmore and Youanmite are yet to show rainfall getting to 30cm and linking up with deeper moisture.
Sites which had greater than 25mm in one event, generally saw moisture soaking to 30 centimetres or lower.
Model distribution summary for the next three months
Graphs showing the distribution of global model forecasts for July-September, with models leaning towards drier rainfall and average-warmer temperatures.
Model distribution summary for the next four to six months
Graphs showing the distribution of October to December forecasts with an increased number of models leaning towards drier rainfall and warmer to average temperatures.
Model consensus forecast for the next six months
|Current outlook (to 26 June)||Previous outlook (to 28 May)|
|July–Sept||Oct–Dec||June–Aug outlook||Sept–Nov outlook|
|Pacific Ocean||Slightly warm||Slightly warm||El Niño (Modoki)||Slightly warm|
|Indian Ocean||Cold (+IOD)||Neutral||Slightly warmer/ neutral (+IOD)||Mixed (possible +IOD)|
|Rainfall||Slightly drier||Slightly drier||Slightly drier/average||Slightly drier|
|Temperature||Slightly warmer/average||Slightly warmer/average||Slightly warmer||Slightly warmer|
Sea surface temperature anomalies
Sea surface temperatures (SST) along the Equatorial Pacific have cooled a little over June and have risen to neutral temperatures.
NINO3 is at +0.42oC and NINO3.4 is +0.62oC (as of 28 June), the threshold for an El Niño is +0.8oC.
The Dipole Mode Index (DMI) measure of the IOD was in positive territory but has recently dropped back to +0.26 (as of 28 June), the threshold for +IOD is +0.4oC.
There has been some cooling of recent times of the African coast but temperatures off Indonesia are looking more classically +IOD in pattern.
Equatorial Pacific sub-sea temperature anomalies
The Pacific Ocean Equatorial sub-surface temperatures have increased a little due to a westerly wind burst early in the month.
This continues to be a very weak El Niño signature.
Southern Oscillation Index
The SOI value is currently at -8.5 (as at 28 June) and spent much of June in weak to moderate positive territory (El Niño SOI level kicks in at negative 8 and beyond).
While this suggest pressure patterns around the Equator are like El Niño the main driver is increased pressure off Darwin not in conjunction with lower pressure of Tahiti.
Pacific Ocean surface wind anomalies
The Equatorial Pacific Easterly Trade Winds had some weak reversal early in the month which sent some slight warming under the Pacific.
At the moment the Trade Winds are behaving normally.
World cloudiness anomalies
Cloud at the International Dateline (180oW) junction with the Equator is slightly greater (blue colour) similar to the last three months.
Usually a sign of El Niño, but the westward extent of this extra cloud is not in keeping with a classic El Niño.
The lack of cloud (brown colours) off Indonesia and the greater cloud off Africa is a classic +IOD pattern.
Southern Annular Mode
The Southern Annular Mode (SAM) started negative but has remained positive for the last three weeks. A positive SAM would usually be associated with weaker frontal activity over southern Victoria during winter.
In the past 30 days, the Sub Tropical Ridge of High Pressure has been at a normal winter position (level with the top of the Bight).
This has allowed fronts and rainfall triggers through, but mainly in southern areas.
If the high-pressure centre was to move over Victoria or move further south, a drier month, particularly in northern areas would be expected.
Air pressure anomalies
The Sub Tropical Ridge of High Pressure was much higher over the whole country.
Stronger pressure highs tend to move more slowly and create blockages to the passage of fronts and lows from the west.
Pressure has been higher to the north of Australia making it harder to drag moisture down.
The higher pressure at Darwin and the normal pressure at Tahiti are why the SOI is negative.
Modelled climate and ocean predictions for Victoria from June 2019 run models
12 climate models show their predictions for the next six months for the Pacific Ocean, Indian Ocean, rainfall and temperature for Victoria.