The seasonal outlooks presented in this report are obtained from the Australian Bureau of Meteorology & 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 & decision making. Changes in seasonal outlooks may have occurred since this report was released. Outlook information was up to date as at 12 May 2015.

Changes in seasonal outlooks may have occurred since this report was released. Outlook information was up to date as at 3rd December 2013.

NSW Climate Summary - May 2015Summary Seasonal outlook Current

Outlook Previous Outlook

Rainfall (quarter) Wetter Wetter Near neutral – neutral (central to north coast)

Max Temperature (quarter)

Cooler (western and areas of central NSW) Near neutral (southern, eastern, most of central NSW) Warmer (far south east)

Warmer (eastern and east-central NSW) Near neutral (western, northern and central NSW)

Min Temperature (qtr) Warmer Warmer

ENSO

ENSO (overall) El Niño Neutral – probable El Niño developing in winter (NOAA - weak El Niño)

BoM ENSO Tracker Status

El Niño El Niño Alert

SOI Negative Neutral (negative)

Pacific Ocean (NINO3.4)

Warm (Above El Niño thresholds)

Warm (currently neutral, but near El Niño thresholds and warming)

Indian Ocean (IOD) Neutral Neutral

Southern Annular Mode (SAM/AAO)

Near neutral – weakly negative

Near neutral – weakly positive

Source: Derived from information provided by the Australian Bureau of Meteorology and the US National Oceanic & Atmospheric Administration.

Seasonal outlook (Source: Bureau of Meteorology)

Between May to July, wetter than normal conditions are likely over most of NSW. Warm sea temperatures around Australia and in the eastern Indian Ocean are contributing to a positive rainfall outlook. Cooler than normal daytime temperatures are likely over the northern and central areas of the far west, and areas of the central west and north west. There is a near equal chance of cooler or warmer than normal daytime temperatures for most of eastern and southern NSW.

Warmer than normal daytime temperatures are likely in the far south east. Warmer than normal overnight temperatures are likely across NSW.

NSW Climate Summary - May 2015

2 NSW Department of Primary Industries, May 2015

ENSO (Source: Bureau of Meteorology & International Research Institute for Climate and Society)

The Bureau of Meteorology has indicated the Pacific is in the early stages of an El Niño event. The Bureau’s ENSO tracker status is at ‘El Niño’. NOAA CPC/IRI indicated that (based on their thresholds) a weak El Niño event commenced in February and may develop into a moderate event. Warm sea surface temperature anomalies extend across nearly all the equatorial Pacific and temperatures are well above the Bureau’s El Niño thresholds. Sub-surface warm temperature anomalies remain across most of the central to eastern Pacific, warming the sea surface. A cool anomaly has strengthened at depth in the west. The SOI is currently negative. Westerly wind anomalies extend across the western equatorial Pacific and cloud has built up at the junction of the International Date Line and equator. The trade winds, SOI and cloudiness are indicative of atmospheric coupling with the ocean in an El Niño event.

NOAA CPC/IRI remains on ‘El Niño advisory’, flagging an El Niño event. The CPC/IRI consensus ENSO forecast probabilities indicates that about 90% of global climate models consider El Niño conditions are likely to continue into winter, and 80% through 2015. The CPC/IRI uses a NINO3.4 anomaly of +0.5°C as an El Niño threshold, while the Bureau of Meteorology uses +0.8°C.

The Bureau of Meteorology’s POAMA outlook (as at 10 May) indicates that the sea surface temperatures in the NINO3.4 Pacific Ocean region are likely remain above the El Niño thresholds during winter and early spring. All eight climate models surveyed by the Bureau (as at 16 April) indicate sea surface temperatures are likely to remain above the thresholds in July-September.

Monthly Sea Surface Temperatures (Source: NOAA & Bureau of Meteorology)

Sea surface temperatures have continued to warm, particularly in the central and eastern equatorial Pacific. The most recent monthly temperature anomaly value in the key NINO3.4 region is +0.78°C for April, an increase from +0.58°C for March. The weekly value to 10 May is +0.97°C.

Monthly Sub-surface Temperatures The sea sub-surface temperatures show the eastwards progression of a strong warm anomaly in the equatorial Pacific since early in the year (a downwelling Kelvin wave) and its warming of the sea surface. Sub-surface warm anomalies now extend across the central and eastern equatorial Pacific. A small cool anomaly remains at depth in the west.

Southern Oscillation Index (SOI) (Source: Bureau of Meteorology & Queensland Department of Science, Information Technology, Innovation & the Arts)

The Southern Oscillation Index (SOI) fell during mid-late March to be strongly negative, returned to neutral levels in mid-April but fell again in early May. As at 11 May, the 30-day value was negative at -11.4.

NSW Climate Summary - May 2015

3 NSW Department of Primary Industries, May 2015

Values of between -8 and +8 indicate neutral conditions, sustained values above +8 may indicate a La Niña event, and sustained values below -8 may indicate an El Niño event.

Indian Ocean Dipole (IOD) (Source: Bureau of Meteorology)

The Indian Ocean Dipole (IOD) is currently neutral. The IOD index value is +0.15°C for the week ending 10 May.

The Bureau of Meteorology’s POAMA model outlook indicates IOD index values may be close to a positive level in spring. Three other climate models surveyed by the Bureau currently favour the IOD remaining neutral though to spring and one favours a strongly negative IOD from July-September.

A negative IOD increases the chances of above normal rainfall during winter and spring across southern and much of western and central NSW. A positive IOD increases the chances of below normal rainfall.

Sub-Tropical Ridge (STR) (Source: NOAA & Bureau of Meteorology) The sub-tropical ridge in the 30 days to 12 May was at close to the normal latitude for the time of year. Atmospheric pressure over NSW during April was lower in the east, particularly across the Illawarra to mid-north coast and slightly higher in the far west, as indicated on NOAA and Bureau of Meteorology mean sea level pressure charts. High pressure may contribute to decreased rainfall.

The sub-tropical ridge is a zone of high pressure which between January and March is normally located south of Australia at about 38°S to 39°S, and can tend to suppress cold front activity. During June to September, it generally moves northwards to around 30°S to 32°S, allowing cold fronts to extend further into southern Australia. It has most effect on winter rainfall.

Cloudiness and trade winds (Source: Bureau of Meteorology)

Cloud at the junction of the International Date Line and equator over the last month is consistent with an El Niño event, although levels across southern Indonesia are not. Trade winds in the western equatorial Pacific show a reversal consistent with an El Niño event.

Southern Annular Mode (SAM) (Source: Bureau of Meteorology [experimental] & NOAA)

The experimental Southern Annular Mode or Antarctic Oscillation (AAO) index is currently near neutral at 10-12 May. The outlook from POAMA indicates the SAM index will rise to be weakly positive, and then fall to be weakly negative in mid-late May. The NOAA outlook suggests a return to weakly positive values in late May.

A negative SAM indicates an expansion of the belt of strong westerly winds towards the equator, resulting in more or stronger low pressure systems across southern Australia and potentially increased rainfall. A positive SAM indicates the contraction of the belt of strong westerly winds towards Antarctica and higher pressures over southern Australia, and can result in stable, drier conditions.

NSW Climate Summary - May 2015

4 NSW Department of Primary Industries, May 2015

Conditions during April Rainfall (Source: Queensland DSITIA)

Rainfall across NSW ranged between 8-535 mm during April, with heavy falls in the east as a result of the East Coast Lows. Much of central NSW received 25-100 mm. Rainfall was less across the northern areas of western, NSW. Relative to historical records, rainfall during April was above average across 79 per cent of NSW.

Soil moisture (Source: CSIRO)

Modelled topsoil moisture levels improved across eastern and central NSW during April. Relative to historical records, levels were above average across much central and eastern NSW. The north coast, western Riverina and much of the far west had average relative topsoil moisture. Modelled subsoil moisture levels were generally stable, but remained low in areas of the north and west. Relative to historical records, subsoil moisture was below average across much of the north west and areas of the northern tablelands, Liverpool plains, the central tablelands and Riverina. Relative subsoil moisture levels were extremely low across the north west.

Pasture growth (Source: Queensland DSITIA)

Relative pasture growth during April improved across most of western, central and south eastern NSW. Across the central to north coast and the eastern fall, growth remained near average. Relative growth improved to well above average across much of the northern slopes, the east of the northern plains, the central tablelands, central west slopes, and the southern tablelands. Relative growth remained low in areas of the north west.

More information For more information, contact the NSW Department of Primary Industries on 02 6391 3100 or Local Land Services on 1300 795 299. Additional and more detailed information on seasonal conditions can be found in the NSW Seasonal Conditions Report, available at http://www.dpi.nsw.gov.au/agriculture/emergency/seasonal-conditions/regional-seasonal-conditions-reports.

Acknowledgements Information used in this report was sourced from the Australian Bureau of Meteorology, CSIRO, Queensland Department of Science, Information Technology and Innovation, the US National Oceanic and Atmospheric Administration, the International Research Institute for Climate and Society (Columbia University) and NSW Department of Primary Industries.

Warning 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.

© State of New South Wales through the Department of Trade and Investment, Regional Infrastructure and Services, 2015. You may copy, distribute and otherwise freely deal with this publication for any purpose, provided that you attribute the NSW Department of Primary Industries as the owner. Disclaimer: The information contained in this publication is based on knowledge and understanding at the time of writing (May 2015). 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 or the user’s independent adviser. Published by the Department of Primary Industries. ISSN 2203-5060 (Online) PUB15/155 Volume 2/Number 4