Australia in December 2009

In Brief

December 2009 saw above-normal temperatures over most of Australia, although not to the extent seen in November, while rainfall was also above normal over large parts of the country, mostly because of either the direct or indirect impacts of Tropical Cyclone Laurence.


Temperatures

Mean maximum temperatures averaged over Australia were 0.77C above normal (10th highest on record), with Western Australia (anomaly +1.14C) ranking as third-warmest on record. Maxima were above normal over most of the country. The largest exception was an area in central Australia covering much of the southern half of the Northern Territory, the far north of South Australia and the far south-west of Queensland, where temperatures locally reached 1C below normal. The only other below-normal areas were parts of the north and west Kimberley affected by TC Laurence, and a few patches in north-western New South Wales.

The most significant warmth was in the southern two-thirds of Western Australia. Maxima were at least 1C above normal over most of this region, reaching 3C above normal along the west coast near Geraldton. Records were set in this area, as well as in parts of the Pilbara near Roebourne and Karratha. Maxima were also at least 1C above normal in much of southern and eastern Australia, encompassing the southern half of South Australia, most of Victoria, New South Wales away from the north-west, south-eastern Queensland and eastern Tasmania. Anomalies in this region locally reached +2C in various regions near the Great Dividing Range from the Darling Downs in southern Queensland to north-eastern Victoria.

Minimum temperatures over Australia were 0.67C above normal (8th highest on record). Again Western Australia was the most extreme state, with the statewide anomaly of +0.90C ranking as fourth-highest on record. As for maxima, above-normal temperatures covered most of the country, with the most substantial exceptions occurring in central Australia, notably in north-eastern South Australia and far south-western Queensland, where minima were 1C or more below normal near Birdsville. Other areas where minima were cooler than normal were the far south-west of Western Australia, and a few patches in that states north and the central Northern Territory.

There were two major areas where minima were at least 1C above normal. One covered much of the southern half of Western Australia away from the south-west corner, with anomalies exceeding 2C around Geraldton. The other covered an area which included most of New South Wales away from the north-west and the southern border, and a belt extending north-west to south-east across Queensland, from the south-east to the Longreach area and then north to the Gulf of Carpentaria. In the latter area minima were 2-3C above normal in a narrow inland corridor extending from Longreach through Mitchell to St. George, with records set across this area.


Areal average temperatures
  Maximum Temperature Minimum Temperature
Rank
(out of 60)
Anomaly*
(°C)
Comment Rank
(out of 60)
Anomaly*
(°C)
Comment
Australia 51 +0.77 53 +0.67
Queensland 46 +0.81 52 +0.87
New South Wales 49 +1.37 48 +0.89
Victoria 50 +1.65 47 +0.64
Tasmania 47 +1.20 23 −0.33
South Australia 41 +0.60 36 +0.51
Western Australia 58 +1.14 3rd highest; highest since 1976 57 +0.90 Highest since 1979
Northern Territory 24 −0.42 30 −0.01

*Anomaly is the departure from the long-term (1961-1990) average.


Temperature maps
MeanAnomalyDeciles
Mean
daily
maximum
temperatures
Map of mean daily maximum temperature Map of mean daily maximum temperature anomalies Map of mean daily maximum temperature deciles
Mean
daily
minimum
temperatures
Map of mean daily minimum temperature Map of mean daily minimum temperature anomalies Map of mean daily minimum temperature deciles

Rainfall

Nationally, rainfall was 22% above normal (35th highest of 110 years). Much of this rainfall resulted from the long-lived circulation associated with Tropical Cyclone Laurence, which reached category 5 status twice and made landfall, first in the Kimberley and then, after moving back out to sea, between Broome and Port Hedland. The precursor circulation to Laurence resulted in heavy rain in the Top End of the Northern Territory; after crossing the north and west Kimberley and a path across the interior of Western Australia as a cyclone, the remnant system crossed northern South Australia, before providing an infeed of moisture into a trough which caused widespread heavy rain in inland New South Wales and Queensland during the last week of the month.

The most prominent wet areas were in the regions affected by Laurence, with totals reaching the highest decile in parts of the Kimberley and Pilbara in Western Australia, an inland eastern belt extending from Dubbo through Charleville to Longreach, some areas around Darwin, and the region west of Oodnadatta in South Australia. They also reached the highest decile in parts of the New England region. Records were set locally in the Kimberley, especially east of Derby and around Mitchell Plateau. Nevertheless, no statewide total was in the highest 20.

Many areas which were not significantly influenced by Laurence had below-normal rainfall, especially in the south-east, including most of Victoria and Tasmania, coastal New South Wales from the Hunter southwards, and South Australia away from the far north. Most of Western Australia south of a Port Hedland-Kalgoorlie line also had below-normal rainfall, although much of this area is seasonally dry; only the south-west coast, between Jurien Bay and Albany, was in the lowest decile (the regional average for south-western WA, 79% below normal, was the 10th lowest on record). A third major dry area was eastern Queensland within about 300 kilometres of the coast (including most of Cape York Peninsula), except for areas between Rockhampton and Hervey Bay, and locally around Townsville. There were smaller dry regions in the southern Northern Territory, the NT part of the Gulf of Carpentaria coast and adjacent north-western Queensland, and in parts of the east Kimberley and adjacent NT areas too far south to be affected by Laurence.


Areal average rainfall
Rank
(out of 110)
Average
(mm)
Departure
from mean*
Comment
Australia 76 62.4 +22%
Queensland 58 81.1 −2%
New South Wales 88 74.3 +46%
Victoria 39 31.6 −34%
Tasmania 37 78.2 −27%
South Australia 79 23.5 +24%
Western Australia 85 50.5 +73%
Northern Territory 66 86.7 +18%
Murray-Darling Basin 88 68.4 +49%

*The mean is calculated for the 1961-1990 reference period.


Rainfall maps
TotalsPercentagesDeciles
Total
rainfall
Map of total rainfall Map of percentage of normal rain Map of rainfall deciles


Australian weather extremes in December 2009
Hottest day 47.0 °C at Hyden (WA) on the 29th
Coldest day 4.7 °C at Mount Baw Baw (Vic) on the 11th
Coldest night −4.1 °C at Charlotte Pass (NSW) on the 2nd
Warmest night 32.9 °C at Wittenoom (WA) on the 31st
Wettest day 402.0 mm at Napier Downs (WA) on the 18th


Notes

The Monthly Climate Summary is prepared to list the main features of the weather in Australia using the most timely and accurate information available on the date of publication; it will generally not be updated.

This statement has been prepared based on information available at 12 pm on Monday 4 January 2010. Some checks have been made on the data, but it is possible that results will change as new information becomes available, especially for rainfall where much more data becomes available as returns are received from volunteers.

Long-term averages in this statement and associated tables are for the period 1961 to 1990 unless otherwise specified.

In the tables, fractional ranks denote tied values.

A new area-averaging method was adopted for rainfall in May 2009. Current and historical totals for Tasmania are substantially higher than under the old scheme, but differences for other states, and nationally, are negligible. The rankings and departures from mean shown here use the new method.


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