NSW Seasonal Conditions Summary September 2017

Overview

During August, rainfall was below average across 33 per cent of NSW, with the north east of the state receiving the lowest rainfall. Most of the north coast, northern tablelands and areas of the Hunter valley and northern slopes received rainfall ranking in the lowest 10-20 per cent of years. Areas of the north west plains, central tablelands, central west, far west and Sydney basin also received below average rainfall. Several areas in the north east experienced their driest August on record or the driest August for the last 20 years.

Although rainfall was near-average across 58 per cent of NSW, it was in the lower end of the range (ranking in the lowest 30-40 per cent of years) across areas of northern, central and western NSW the western Riverina, Hunter valley and Sydney basin.

The far south of the state received above average rainfall for the period, together with the alpine areas and isolated areas of the southern tablelands and Monaro.

Over the last three months, rainfall was below average across 85 per cent of the state. It was well below average to extremely low across most of inland NSW and the south east, with many areas (particularly in central NSW) receiving rainfall in the lowest 10 per cent of years.

Pasture growth remained limited across much of inland NSW as a result of the continued warmer than normal daytime temperatures combined with a lack of topsoil moisture, frosts and grazing pressure. Levels of growth improved across some areas of southern NSW but declined across areas of the coast.

Relative to historical records, pasture growth was well below average across large areas of western, north western and central NSW as well as the Hunter valley and north coast. Growth was average to slightly above average across areas of the south.

Other pasture growth models indicated extremely low growth across most of NSW, with near-average growth for areas of the far south and south west.

Pasture biomass was relatively unchanged during August. It remained low across most of NSW, with the exception of areas of the south. Relative to historical records, biomass was generally below average across areas of north western and central NSW, the Hunter valley, southern tablelands and the central Riverina.

Limited rainfall in August and multiple frosts saw winter crop prospects continue to decline. West of the Newell Highway across north western and central western NSW and areas of the Riverina, many crops have been abandoned. In areas of the north west and northern central west, many of those winter crops that had sufficient soil moisture to maintain growth were affected by frosting.

In eastern areas, more rainfall was received during August but was generally insufficient to replenish depleted topsoil moisture reserves. A combination of warm daytime temperatures and multiple frosts (particularly in late August) put pressure on crops, progressively reducing the yield potential of winter cereals and canola. Growers in a number of areas will need to make difficult decisions soon on whether to persist with crops or to graze them or cut them for hay. Areas of the eastern Riverina, south west slopes and the Murray valley received sufficient rainfall during August to maintain crop yield potential, but above average follow up rainfall is likely to be required.

Prospects for dryland summer cropping across many areas of northern NSW are poor, with August and early September rainfall insufficient to replenish depleted subsoil moisture reserves. Significant rainfall will be required during September to allow a dryland summer crop to be sown in northern NSW.

During August, topsoil moisture remained low but mostly stable in areas of western and central NSW, but declined across the north and the central to north coast. Particular declines occurred across the north coast, Hunter valley and northern tablelands. Topsoil moisture improved across areas of the south, eastern and central Riverina, southern tablelands, Monaro and south east. Relative to historical records, topsoil moisture was below average across most of northern, north eastern and central NSW, as well as the central to north coast and areas of the far west and western Riverina. Topsoil moisture was near-average across areas of the far west, the eastern and central Riverina, the far south and the south east of NSW.

Run off during August was near average across most of inland NSW, with above average run off across areas of southern NSW, the south east and the south of the central west. Run off was below average across the north coast, northern tablelands and slopes and the Hunter valley.

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Seasonal outlook

The Bureau of Meteorology’s rainfall outlook for September to November (see the Climatic Outlook Summary below) indicates there is a near-equal chance of drier or wetter than normal conditions across most of NSW. Wetter than normal conditions are likely in the far north east and areas of the south east.

There is a near-equal chance of cooler or warmer than normal daytime temperatures across most of northern and western NSW and the north of the central west. Warmer than normal daytime temperatures are likely across most of the Riverina, far south, central and southern tablelands, Hunter valley, south coast and Monaro, as well as an area of the far north east.

Overnight temperatures are likely to be warmer than normal across most of NSW. There is a near-equal chance of cooler or warmer than normal conditions for areas of the far west.

During September, there is a near-equal chance of drier or wetter than normal conditions across NSW. Warmer than normal daytime temperatures are likely across most of NSW, with a near-equal chance of cooler or warmer than normal temperatures in areas of the far west. Overnight temperatures are likely to be warmer than normal.

More recent (unreleased) updates to the outlooks indicate drier than normal conditions are likely for September.

With both the El Niño-Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD) remaining neutral, these outlooks have been influenced other climate drivers. Influences include warmer sea surface temperatures along the east of the continent and cooler sea surface temperatures in the eastern Indian Ocean. Other influences include the prospect of high atmospheric pressure south of the continent and the possibility of a positive Southern Annular Mode. These contribute to the likelihood of greater easterly flow across southern Australia.

The NOAA Climate Forecast System (CFS) rainfall outlook for September to November is near-neutral (that is, a near equal chance of drier or wetter than normal conditions) for NSW. Wetter than normal conditions are possible along the coastal strip of the south to central coast. The overall temperature outlook is near-neutral for most of NSW. Warmer than normal conditions are possible for areas of the far north east and adjacent to the coast. Cooler than normal conditions are possible for areas of the southern tablelands and the alpine areas.

For September, the CFS rainfall outlook is near-neutral for the southern half of NSW. Drier than normal conditions are possible for the north and areas of the northern central west and Hunter valley. The overall temperature outlook is near-neutral for most of NSW, with warmer than normal temperatures possible for the far north east.

A survey of the major global climate models in early September indicated that for most of NSW a slight majority of models (55 per cent) favoured a generally near-neutral outlook for the September to November period (a near-equal chance of drier or wetter than normal conditions). Most of the remainder favoured a generally drier than normal outlook with one favouring slightly wetter than normal conditions. For temperature, 64 per cent of models favoured a warmer than normal outlook, with the remainder favouring a near-neutral outlook.

Of the major multi-model ensembles surveyed, most favoured a near-neutral rainfall outlook for the September to November period, with one favouring a drier than normal outlook. Over the period, the multi-model ensembles were split between warmer than normal and near-neutral conditions.

Overall NSW outlook -
major climate models

Rainfall Outlook
(number of models)

Temperature Outlook
(number of models)

Period

Generally wetter

Generally
near-neutral

Generally
drier

Generally
warmer

Generally
near-neutral

Generally
cooler

September – November

1

6

4

7

4

0

October – December

0

8

0

5

3

0

The AussieGRASS pasture growth outlook for September to November suggests that near-average to slightly above average growth is possible for most of NSW, with slightly below to below average growth for some areas of the far south and north west.

The SOI phase seasonal rainfall outlook that the growth outlook is based upon is wetter than normal for most of NSW during September to November. This was based on a consistently positive SOI phase during July and August. In comparison, the Bureau of Meteorology’s September to November rainfall outlook suggests a near-equal chance of drier or wetter than normal conditions across NSW. Potential growth may therefore be very different from the pasture growth outlook.

The current growth outlook has a high past accuracy across most of NSW.

El Niño Southern Oscillation (ENSO)

The Pacific Ocean remains in an ENSO-neutral state, with the outlook from most global climate models suggesting ENSO neutral conditions will continue throughout 2017.

The Bureau of Meteorology’s ENSO outlook status is currently ‘Inactive’. The CPC/IRI also indicate that ENSO neutral conditions are present and are likely to continue throughout spring. Note that the Bureau and CPC/IRI use different ENSO thresholds.

The Indian Ocean Dipole (IOD) is also neutral. Some models indicate that a positive or borderline positive IOD event is possible in early spring. Positive IOD events tend to suppress rainfall across Australia during spring, with even borderline events having some effect.

Sea-surface temperatures across the eastern and central equatorial Pacific are slightly below average to near-average, with slightly warmer than average temperatures in the west. In the Indian Ocean, sea surface temperatures remain slightly above average in the west and below average in areas of the east. Sea surface temperatures are cool to the west of Australia, and warm to the north and east, with warm temperatures in the Coral Sea.

In the sub-surface, conditions are La Niña-like. Areas of weak warm anomalies are present across the western equatorial Pacific. A large cool anomaly has strengthened, and extends from the western equatorial Pacific through the central equatorial Pacific to the surface in the east. A small area of warm anomalies is present in the far east at the surface.

The easterly trade winds were close to normal throughout August, with some strengthening in the west, contributing to warmer sea surface temperatures in the western equatorial Pacific.

The Southern Oscillation Index (SOI) is currently near-neutral (borderline positive), and remained neutral throughout most of August, with atmospheric pressure close to normal at Darwin and slightly above normal at Tahiti.

Atmospheric pressure was at more normal levels across Australia during August, with somewhat lower than normal pressure in the Great Australian Bight and across southern Australia.

The Southern Annular Mode (SAM) was variable, moving from strongly positive early in August to near-neutral mid-month and moderately to strongly positive late month. With the high atmospheric pressure, the SAM had a major influence on rainfall patterns across NSW during the month.

The SAM is currently weakly positive and is expected to be near-neutral into late September.

However, the overall outlook suggests the likelihood of the SAM returning to positive levels. A positive SAM during winter and early spring acts to drag cold fronts to the south, reducing the likelihood of them passing over southern Australia. Later in spring and summer, a positive SAM can be linked to higher than normal rainfall over south eastern Australia.

Under ENSO-neutral and IOD-neutral conditions, other influences such as the SAM, atmospheric pressure and sea surface temperatures near the continent tend to have a greater effect on the climate.

Climatic outlook summary

NSW Seasonal Outlook (BoM)

Current outlook

Previous outlook

Quarterly Rainfall

Near-neutral

(most of NSW)

Wetter

(Areas of the far north east and south east)

Drier

(most of western, central and southern NSW and areas of the south east)

Near-neutral

(most of eastern and northern NSW and areas of the central west)

Quarterly Maximum Temperature

Near-neutral

(most of western and northern NSW and the northern central west)

Warmer

(most of the south, south east, Riverina, southern central west, central and southern tablelands, south to mid-north coast, Hunter valley and far north east)

Warmer

Quarterly Minimum Temperature

Warmer

(most of NSW)

Near-neutral

(areas of the far west)

Warmer

El Niño Southern Oscillation (ENSO)

ENSO (overall)

Neutral

Neutral

BoM ENSO Outlook Status

Inactive

Inactive

Southern Oscillation Index (SOI)

Neutral

(borderline positive)

Neutral

Pacific Ocean (NINO3.4)

Neutral

(slightly cool)

Neutral

Indian Ocean (IOD)

Neutral

(western Indian Ocean slightly warm, eastern slightly cool)

Neutral (weakly positive)

(western Indian Ocean warm, eastern slightly cool)

Southern Annular Mode (SAM/AAO)

Weakly positive

(trending weakly positive to near neutral, but with a generally positive outlook)

Neutral

(trending from weakly-moderately positive to near neutral, but with a positive outlook throughout winter)

Note: Climate model outlooks are updated twice monthly. To check whether updates are available, use the hyperlinks provided.

Rainfall and temperature

Rainfall for all of NSW during August was 44 per cent below average, making it the driest August for the last four years. Rainfall across the state ranged from 0-262 mm. Most of northern, central and western NSW, the Hunter valley and the Sydney basin received between 5-25 mm. Apart from areas of the south, rainfall was generally light and patchy. Most falls occurred early and mid-month.

The best falls occurred mid-month in the south of the state, including areas of the Murray valley, eastern to central Riverina, southern and central tablelands, alpine areas and south coast. Rainfall ranged from 25-50 mm across the far south west, central Riverina, areas of the central tablelands and areas of the south coast, southern highlands and Monaro. The alpine areas and areas of the south west slopes, far south and southern and central tablelands received over 50 mm. Most areas of the central west, north west and Hunter valley received 10-25 mm, with the far west generally receiving 0-10 mm in the north but 10-25 mm in the south. The northern tablelands received 1-25 mm. The lowest rainfall for the state of 0-5 mm occurred across the north coast, with some areas recording their driest August on record.

Daytime temperatures were above average during August in the north of the state, particularly in the north east. Temperatures were below average in the south and near-average in central and western areas of NSW.

Overnight temperatures were below average to well below average across most of inland NSW, but near average over areas of the east. A number of frosts occurred during the month, particularly in the final week, with the most severe frosts occurring around 20, 28 and 29 August.

Relative rainfall

Rainfall across NSW during August was below average across 33 per cent of the state, with the north east receiving the lowest rainfall. Most of the north coast, northern tablelands, and areas of the Hunter valley and northern slopes received rainfall ranking in the lowest 10-20 per cent of years.

Rainfall was also below average across areas of the north-western plains, central west, far west, central tablelands and Sydney basin.

Although rainfall was near-average across 58 per cent of NSW, it was in the lower end of the range (ranking in the lowest 30-40 per cent of years) across areas of northern, central and western NSW the western Riverina, Hunter valley and Sydney basin.

Areas of the Murray valley and the alpine areas received above average relative rainfall for the month.

Over the last three months, relative rainfall was below average across 85 per cent of the state and near-average across 14 per cent, with above average rainfall restricted to just 1 per cent of the state. During this period, rainfall was well below average to extremely low across most of inland NSW and the south east. Many areas (particularly in central NSW) received rainfall in the lowest 10 per cent of years. Rainfall was near-average across the north coast and areas of the Sydney basin, lower Hunter valley and the east of the northern tablelands.

Soil moisture

During August, topsoil moisture remained stable in western and central NSW, but declined across the north and the central to north coast. Particular declines occurred across the north coast, Hunter valley and northern tablelands. Topsoil moisture improved across areas of the south, eastern and central Riverina, southern tablelands, Monaro and south east.

Relative to historical records, topsoil moisture was below average across most of northern, north eastern and central NSW, as well as the central to north coast and areas of the far west and western Riverina. Topsoil moisture was near-average across areas of the far west, the eastern and central Riverina, the far south and the south east of NSW.

The most reliable soil moisture models indicated further declines in subsoil moisture across much of inland NSW during August, with some improvement across the far south, south west slopes and southern tablelands. With these models, relative to historical records subsoil moisture was below to well below average across most of inland and south eastern NSW, the Sydney basin and the Hunter valley. Subsoil moisture was near-average across areas of the far south. Other models suggested a decline to mostly near-average levels across inland NSW, with above average levels across some area of the far west and south.

Streamflow

Run off during August was near average across most of inland NSW, with above average run off across areas of southern NSW, the south east and the south of the central west. Run off was below average across the north coast, northern tablelands and slopes and Hunter valley.

Yearly run off to August remained influenced by the wet conditions in 2016. It was above average to extremely high across much of western and southern NSW and across the areas of the tablelands, northern slopes and far north coast. Run off was below average across areas of the north west, central west, Hunter valley and the far south coast.

The Bureau of Meteorology's streamflow forecast indicates low to near-median streamflows are likely at most NSW monitoring stations during September to November. Near-median to above median streamflows are likely at some north eastern locations.

Relative pasture growth and biomass

Relative to historical records, AussieGRASS modelled pasture growth during August was below average across areas of western NSW, the north west, tablelands and much of the central west, north coast and Hunter valley. Growth was near-average elsewhere, but average to slightly above average in the far south, areas of the Riverina and the south east.

Other pasture growth models indicated well below average to extremely low growth across the majority of NSW, apart from average growth across areas of the far south and south west.

The Pastures from Space model indicates a mean pasture growth of less than 10 kg/ha/day during late August across most Local Government Areas of NSW, apart from those in the Murray Valley and Riverina.

Over the quarter, AussieGRASS relative growth was below average across most of the far west, central west, the north west (west of the Newell Highway), the Hunter valley and areas of the central Riverina and the southern and central tablelands. Growth was near-average in most other areas.

During August, relative biomass levels were below average across areas of the north west, central west, Hunter valley, Sydney basin, central Riverina, and central and southern. Levels were above average across limited areas of the far south east, far south and northern tablelands, and near-average elsewhere.


Figure 1: Relative monthly topsoil moisture

 Small map of relative soil moisture (upper level) - average value for July 2017

Figure 2: Relative quarterly pasture growth

Small map of pasture growth relative to historical records from 1957 - May 2017 to July 2017

More information

For more information, contact the NSW Department of Primary Industries on 02 6391 3100 or Local Land Services on 1300 795 299.

Acknowledgements

Information used in this report was sourced from the Australian Bureau of Meteorology, CSIRO, the Queensland Department of Science, Information Technology and Innovation, the Queensland Alliance for Agriculture and Food Innovation, the U.S. Department of Agriculture, U.S. Department of Commerce, the U.S. National Oceanic and Atmospheric Administration, the International Research Institute for Climate and Society (Columbia University), the UK Meteorological Office, the APEC Climate Centre, NSW Local Land Services and NSW Department of Primary Industries.

External links

Disclaimer

The seasonal outlooks presented in this report are obtained from the Australian Bureau of Meteorology and other sources. These outlooks are general statements about the likelihood (chance) of (for example) exceeding the median rainfall or minimum or maximum temperatures. Such probability outlooks should not be used as categorical or definitive forecasts, but should be regarded as tools to assist in risk management and decision making. Changes in seasonal outlooks may have occurred since this report was released. Outlook information was up to date as at early September 2017.

Recognising that some of the information in this document is provided by third parties, the State of New South Wales, the author and the publisher take no responsibility for the accuracy, currency, reliability and correctness of any information included in the document provided by third parties.

The information contained in this publication is based on knowledge and understanding at the time of writing (8 September 2017). However, because of advances in knowledge, users are reminded of the need to ensure that information upon which they rely is up to date and to check currency of the information with the appropriate officer of the Department of Primary Industries, Local Land Services or the user’s independent adviser.