Southern NSW

Seasonal climate risk information for Southern NSW

Volume 1 | Issue 6 | 28 June 2019

Southern NSW has had a dryer than normal June. Adequate rainfall has only fallen on the SE of SNSW with this region totalling close to 25 millimetres for June. All other cropping regions received 10-25 which has been barely enough to match evaporation.

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 for SNSW.

Pressure patterns have been unfavourable for much of the central and northern areas and barley OK for the southern areas. Total pressure has also been sub-optimal in term of absolute pressure, i.e. moving slowly and also bringing the odd frost.

The majority of models lean towards higher chances of a drier next three months, with likely warmer temperatures.

Soil moisture

map of Southern NSW showing plant available moisture (%).

Modelled soil moisture has decreased in many parts of SNSW during June due to evaporation and plant growth not being matched by rainfall. The eastern Riverina and far Central West regions have average moisture reserves and all other regions of SNSW are rated as below average for this time. Paddocks that received summer storms with good weed control may have higher amounts.

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 warmer/average temperatures.

Model distribution summary for the next four to six months

Graphs showing the distribution of October-December forecasts with models leaning towards average-drier rainfall with warmer temperatures.

Model consensus forecast for the next six months

Current outlook (to 26 June)

Previous outlook (28 May)

July-Sept

Oct-Dec

Jun-Aug outlook

Sep-Nov outlook

Pacific Ocean

Slightly warm

Slightly warm

El Niño (Modoki)

Slightly warm

Indian Ocean

Cold (+IOD)

Neutral

Neutral (+IOD)

Mixed (poss +IOD)

Rainfall

Slightly drier

Average/ slightly drier

Average

Drier

Temperature

Slightly warmer/average

Slightly warmer

Slightly warmer

Slightly warmer

Sea surface temperature anomalies

Equatorial Pacific Ocean Sea surface temperatures are at neutral levels but a +IOD exists in the Indian Ocean

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

Equatorial undersea temperature anomalies in the Pacific show some weak warming at depth.

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 and stable (as at 28 June)

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 trade winds are behaving normally.

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 is greater at the junction of the Equator with the Dateline.

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 SAM has spent much of June in moderate to weak positive territory.

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 but usually has limited effect on SNSW. It’s probably not helping the situation.

Air pressure

the STR of high pressure has been higher than its normal position around Adelaide.

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 the odd front through, but mainly in southern areas. The position of this high is problematic for central and northern SNSW as its putting downward pressure on frontal systems away from NSW. If the high-pressure centre was to move over Victoria or move further south, a drier month, particularly in northern SNSW might be expected.

Air pressure anomalies

Pressure at Darwin is slightly higher than Tahiti, pressure over SE Australia has been much higher.

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 Southern NSW 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 SNSW
Click here to download this table in MS Word format
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