Thursday 10 January 2019 — Monthly Summary for Australia — Product Code IDCKGC1A00

Australia in December 2018

Temperatures Rainfall Extremes Important notes the top

In brief

• December was the warmest on record for Australia, with prolonged periods of extreme heat
• A Special Climate Statement discussing the extraordinary heat will be released
• Mean maximum temperatures above average for nearly all of Australia, and highest on record for much of the Northern Territory and northern Western Australia
• Mean minimum temperatures were above average for nearly all of Australia, and highest on record for much of the southeast, and parts of northern Australia
• Nationally, December rainfall was below average
• Rainfall for the month was below average across much of the northern half of the country extending into northern New South Wales
• Rainfall was above average rainfall across the northeast coast, large areas of the southeast mainland, and inland southwest
• There were a number of extreme weather events during the month, including heatwaves early and late in the month, extreme rainfall, and severe storms

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Temperatures

December was an exceptionally warm month. It was the warmest December on record for Australia in terms of mean, maximum, and minimum temperatures. The national mean temperature was 2.13 °C above average. Maximum temperatures were 2.41 °C above average and minimum temperatures were 1.85 °C above average.

Both maxima and minima were warmer than average across nearly all of Australia. December was the warmest on record for New South Wales, Victoria, Tasmania, and the Northern Territory. For the remaining States, December was amongst the three warmest on record.

Following a severe heatwave at the end of spring (see Special Climate Statement An extreme heatwave on the tropical Queensland coast), warmth persisted across the north of Australia during the first week of December, with a few stations in the Northern Territory observing their warmest December day on record on between the 4th and 6th. Meanwhile, across the south a short-lived burst of a heat affected coastal South Australia and Victoria, with days more than 12 degrees warmer than average.

Apart from a cool spell over the inland southeast just before mid-month, which saw a few locations in South Australia observe record low daily maximum temperatures on the 13th or 14th, temperatures remained generally above average over much of Australia throughout the month. Heat again built from the 18th, becoming widespread from the 24th.

The last week of the year saw exceptionally high temperatures, affecting very large areas from northwest Australia into the southeastern mainland. Temperatures remained very high for multiple days, especially over northern Australia, and a large number of sites had a record number of consecutive days with a maximum temperature of at least 42 °C. Many locations set new high December temperature records late in the month across the Northern Territory, Western Australia, South Australia, New South Wales, and Victoria. Some broke the previous record several times, and a few broke previous annual records.

The highest temperatures were observed in northwest Western Australia, including 49.3 °C at Marble Bar on the 27th. This was an annual record for Marble Bar, and broke the record it had set only the day before. In terms of area-averaged mean maximum temperature for Australia as a whole, the 27th was the warmest December day on record, and the second warmest on record for any month of the year. A Special Climate Statement discussing the event will be released.

For the month as a whole, December mean maximum temperatures were highest on record for the month across large parts of northern Australia, extending from the inland Pilbara, across the Kimberley and much of the Northern Territory, to northwestern Queensland. Small scattered parts of the southeast mainland also were highest on record. Minimum temperatures were record warm for large parts of northern Australia, and for much of southeastern Australia.

Maximum temperatures were very much above average (in the warmest 10% of historical observations) for the Northern Territory; western Queensland; western, central, and southern New South Wales; Victoria and Tasmania; South Australia except the South Coast District; the northern half of Western Australia away from the coast, and the southeastern corner of Western Australia. Daytime temperatures were near average for much of eastern Queensland and along much of the coast in Western Australia from the Pilbara to the Nullarbor Plain.

Minima were also very much above average (in the warmest 10% of historical observations) for much of Australia — including most of the Northern Territory except parts of the south; most of Queensland except the southeast; New South Wales except the northeast; Victoria and Tasmania; South Australia away from the northwest; and most of the northern half of Western Australia. Minimum temperatures were near average for pockets in northeastern New South Wales and southeastern Queensland, and along a broad strip of coastal Western Australia stretching from the Kimberley coast, around to the Nullarbor Plain.

Temperature maps
	Mean	Anomaly	Deciles
Mean daily maximum temperatures
Mean daily minimum temperatures
Mean daily temperatures

Temperatures Rainfall Extremes Important notes the top

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Rainfall

Rainfall for December was below above average for Australia as a whole. December rainfall was below average across most of Queensland away from the east coast; for northern New South Wales; nearly all of the Northern Territory; most of the Kimberley and Pilbara in Western Australia, and areas of the west inland of the coast; and a large part of South Australia extending from the northeast to the western Eyre Peninsula.

Rainfall for the month was the lowest on record for some locations in the Northern Territory and Queensland.

Rainfall for the month was above average across the east coast of Queensland from Cape York to Rockhampton; most of Victoria, except parts of the south and Gippsland; southwestern New South Wales and some pockets along the east coast; parts of far southeastern South Australia; a large area spanning the southeast of Western Australia, northwestern South Australia, and the far southwest of the Northern Territory; and a pocket surrounding Shark Bay on the west coast of Western Australia.

Severe tropical cyclone Owen during the first half of the month, and to a lesser extent, tropical cyclone Penny at the end of the month, were largely responsible for the above average rainfall in east coast Queensland. Owen produced steady heavy rainfall on its second pass across Cape York Peninsula on the 15th, bringing daily totals of 300 to 500 mm near Ingham on the east coast and localised flash flooding. A number of stations set daily rainfall records for December during the event, with several going on to record their highest total December rainfall on record. The highest total was 678 mm at Halifax (Macrossan Street); a new December daily rainfall record for Australia.

Owen also contributed to the high rainfall over western Victoria by drawing moist tropical air south, resulting in a period of very heavy showers and storms around mid-month. Strong winds, heavy rain, and severe thunderstorms affected Victoria, New South Wales, and Tasmania over the 13th to 16th, with flash flooding in Melbourne, parts of northern and northwestern Victoria, and Sydney. Several stations in western Victoria observed their wettest December day on record during the 24 hours to 9 am on the 14th — some of which went on to be wettest on record for total December rainfall.

During the afternoon and evening of the 20th, the eastern half of New South Wales saw widespread thunderstorm activity, triggered by a low pressure trough moving through a region of high instability, characterised by warm and very humid sub-tropical air. Giant hail, damaging wind and intense bursts of rain was reported in Sydney, the Blue Mountains, and Central Coast regions. Extensive property damage was recorded in greater Sydney.

Area-average rainfall
	Rank (of 119)	Average (mm)	Departure from mean	Comment
Australia	28	40.8	−22%
Queensland	60	77.9	−6%
New South Wales	46	39.0	−27%
Victoria	99	68.4	+44%
Tasmania	56	94.0	−10%
South Australia	62	14.3	−22%
Western Australia	34	23.2	−27%
Northern Territory	15	39.2	−47%
Murray-Darling Basin	50	36.0	−26%

Rank ranges from 1 (lowest) to 119 (highest). A rank marked with ’=‘ indicates the value is tied for that rank. Departure from mean is relative to the long-term (1961–1990) average.

Rainfall maps
	Totals	Percentages	Deciles
Total rainfall

Temperatures Rainfall Extremes Important notes the top

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Australian weather extremes during December 2018
Hottest day	49.3 °C	at Marble Bar (WA) on the 27th
Coldest day	4.6 °C	at Mount Baw Baw (Vic.) on the 2nd
Coldest night	−2.6 °C	at Perisher Valley AWS (NSW) on the 23rd
Warmest night	34.0 °C	at Wittenoom (WA) on the 27th
Wettest day	678.0 mm	at Halifax Macrossan St (Qld) on the 16th

Temperatures Rainfall Extremes Important notes the top

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