Northern Territory in September 2012: "The Build Up"

The month of September is usually the last month of the dry season with increase in temperatures and humidity across the Northern Territory. Typically in September, the sub-tropical ridge weakens as troughs with associated moisture punch into the Territory and the climate begins the transition into the wet season. This month was strongly influenced by the sub-tropical ridge as no rainfall was recorded until the last two days of the month.

  • Dry spell in Alice Springs District ends with 157 days without rain
  • Bushfires char NT
  • "Build Up" is felt in Top End

Dry spell in Alice Springs Airport ends

On September 29th, a record long dry spell of 157 days without rain at Alice Springs Airport, ended as 3.0 mm fell on the 29th and 0.8 mm on the 30th. The rain came as a result of a mobile trough that pushed across the Territory producing a northwest cloudband and brought light rain along with it.

Bushfires

Bushfires in the NT continued throughout the month due to the strong sub-tropical ridge. Dry, gusty southeast and northerly winds along with high fuel load raised the FDI's across the Territory, and several Fire Bans were imposed by the authorities. A total of 52 Fire Bans and 55 Fire Warnings were issued with a few 'extreme' FDI events recorded especially over the Top End.

The Build Up

During the month of September there was a gradual increase in temperatures and humidity indicative of the "build up"or transition into the wet season in the Territory. As an example, the monthly average dew point temperature at Darwin Airport for August was 14.6 °C while the average for September was 19.6 °C. The build up is often characterized as frequent thunderstorms from an hot and humid unstable atmosphere near the surface. While September was mostly dry, without thunderstorms, the first "build up" storm developed in the western Top End on the 30th.

Rainfall

On 29 and 30 September, a mobile trough moved slowly across the NT creating a northwest cloudband on the 29th which brought light rain to the Alice Springs District, ending Alice Springs' 157 day, record long, dry spell. The trough slowly moved north and by the time it reached the Top End, early on the 30th, it not only caused broad scale cloudiness and light rain, but also induced surface based convection in some areas causing significant rainfall which exceeded long term monthly mean for many locations. On the 30th, Channel Island had 31.8 mm, Darwin Airport recorded 23.0 mm, Middle Point measured 39.2 mm and Oenpelli had 20.0 mm. While none of these were records, they were all well above the September monthly mean. Two stations did measure their highest September daily rainfall on record on the 30th. These are Nutwood Downs and Channel Point. Nutwood Downs also measured their highest total September rainfall on record. There is a map of rainfall deciles below.

The wettest overall was Wongalara with 64.8 mm, followed by Nutwood Downs with 47.8 mm, and then Cdu Katherine Rural Campus with 47.0 mm.

The wettest single day was the 30th when the highest falls were at Wongalara with 64.8 mm, followed by Nutwood Downs with 47.8 mm, and then Cdu Katherine Rural Campus with 47.0 mm on the 30th.

Temperature

During the month of September, temperatures gradually increased as the sub-tropical ridge weakened and more solar exposure allowed for surface heating. The mean temperature for September across the Northern Territory was 23.64 °C, which is 1.14 °C warmer than the long-term average.

The warmest on average was Jabiru Airport with 28.8 °C, followed by Delamere Weapons Range with 28.3 °C,and then both Cape Don and Darwin NTC with 28.2 °C. The coolest on average was Arltunga with 18.9 °C, followed by Alice Springs Airport with 19.7 °C, and then Curtin Springs with 19.9 °C.

Maximum temperature

The maximum temperatures across the Northern Territory recorded about 1 to 3 °C greater than the September monthly maximum of 31.38 °C, except along the northwest coast which is just below the average due to the sea breeze. Increasing solar exposure increased the daily maximum temperatures especially across the central Australia (about 4 °C greater then September average) and sea breezes kept the northwest cooler. Some sites, such as Tindal RAAF, and had their highest September temperature on record, while Alice Springs Airport tied their highest September temperature on record. Jabiru had its highest September mean daily maximum temperature on record. There is a map of maximum temperature anomalies below.

The hottest day was at Lajamanu with 41.1 °C on the 23rd, followed by Bulman with 41.0 °C on the 27th, and then Daly Waters with 40.9 °C on the 27th.

The warmest days on average were at Douglas River with 38.0 °C, followed by Noonamah and Timber Creek both with 37.5 °C, and then Jabiru Airport and Middle Point with 37.4 °C.

The coolest days on average were at Arltunga with 28.1 °C, followed by McCluer Island with 29.2 °C, and then North East Island with 29.4 °C.

The coldest day was at Arltunga with 16.5 °C on the 29th, followed by Alice Springs Airport with 18.4 °C on the 29th, and then Jervois with 19.7 °C on the 29th.

Minimum temperature

The minimum temperatures across the Territory were below average for most of the month especially over the Top End. However, in the Alice Springs District the minimum temperatures were above average due to weak troughs with northerly wind flow ahead of the trough which moved across the area.

The coldest night was at Arltunga with -0.4 °C on the 10th, followed by Arltunga with 0.0 °C on the 2nd, and then Arltunga again on the 3rd with 0.5 °C.

The coolest nights on average were at Arltunga with 9.4 °C, followed by Alice Springs Airport with 9.6 °C, and then Curtin Springs with 10.2 °C.

The warmest nights on average were at Darwin NTC and McCluer Island with 24.5 °C, followed by Cape Don with 24.3 °C, and then Cape Wessel with 24.0 °C.

The warmest night was at Timber Creek with 26.3 °C on the 30th, followed by Darwin NTC with 26.0 °C on the 27th, followed by Cape Don with 26.0 °C on the 30th, and then McCluer Island on the 13th and Darwin NTC on the 24th with both recorded 25.8 °C.

There is a map of minimum temperature anomalies below.

Wind

The strongest wind gust was at Central Arnhem Plateau with 72 km/h on the 29th, followed by Walungurru with 70 km/h on the 13th, and then both Ngayawili on the 12th and Territory Grape Farm on the 28th with 67 km/h

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Extremes in September 2012
Hottest day 41.1 °C at Lajamanu on the 23rd
Warmest days on average 38.0 °C at Douglas River
Coolest days on average 28.1 °C at Arltunga
Coldest day 16.5 °C at Arltunga on the 29th
Coldest night -0.4 °C at Arltunga on the 10th
Coolest nights on average 9.4 °C at Arltunga
Warmest nights on average 24.5 °C at Darwin NTC AWS
Warmest night 26.3 °C at Timber Creek on the 30th
Warmest on average overall 28.8 °C at Jabiru Airport
Coolest on average overall 18.9 °C at Arltunga
Wettest overall 64.8 mm at Wongalara
Wettest day 64.8 mm at Wongalara on the 30th
Highest wind gust 72 km/h at Central Arnhem Plateau on the 29th

Maps
ObservedAnomalyDecile rank
Total
rainfall
Map of Rainfall totals Map of Percentage of normal rainfall Map of Rainfall deciles
Mean
daily
maximum
temperatures
Map of Mean maximum temperature Map of Anomaly in mean maximum temperature Map of Decile rank of mean maximum temperature
Mean
daily
minimum
temperatures
Map of Mean minimum temperature Map of Anomaly in mean minimum temperature Map of Decile rank of mean minimum temperature

Click on a map to show it full size in a pop-up window


Record highest September daily rainfall
Highest daily rainfall
in September 2012 (mm)
Previous wettest
for September
Years of
record
Nutwood Downs 47.8 on the 30th 40.8 on the 24th in 1998 75
Channel Point 34.6 on the 30th 17.0 on the 18th in 2002 22



Record highest total September rainfall
Total rainfall
for September 2012 (mm)
Previous wettest
for September
Years of
record
Average for
September
Nutwood Downs 47.8 40.8 in 1998 75 3.9



Record highest September temperature
Highest temperature
in September 2012 (°C)
Previous warmest
for September
Years of
record
Average for
September
Alice Springs Airport 38.8 on the 22nd = 38.8 on the 22nd in 2003 71 27.2
Daly Waters AWS 40.9 on the 27th 40.0 on the 26th in 2003 44 34.6
Tindal RAAF 40.0 on the 27th 39.9 on the 28th in 1992 25 35.7
Territory Grape Farm 38.2 on the 27th 38.0 on the 22nd in 2003 20 30.2



Record highest September mean daily maximum temperature
Mean daily maximum
temperature
for September 2012 (°C)
Previous warmest
for September
Years of
record
Average for
September
Jabiru Airport 37.4 = 37.4 in 2009 34 36.2



Summary statistics for September 2012
Maximum temperatures
for September
(°C)
Minimum temperatures
for September
(°C)
Rainfall
for September
(millimetres)
Mean for
September
2012
Diff
from
average
Highest for
September
2012
Mean for
September
2012
Diff
from
average
Lowest for
September
2012
Total for
September
2012
Average
for
September
Rank of
September
2012
Fraction of
September
average
Darwin-Daly (district 14GA)
Batchelor Aero 36.5 +0.5 38.4 23rd 19.6 -1.1 15.9 3rd 11.6 6.6 high 176%
Black Point 32.1 +0.5 34.2 15th 22.3 -0.8 19.9 2nd 0 1.0 lowest 0%
Cape Don 32.1   33.5 16th 24.3   23.2 8th 0.2 6.5 average 3%
Central Arnhem Plateau 34.9   38.3 27th 17.8   14.2 10th 15.0
Darwin Airport 33.8 +1.2 36.2 9th 21.9 -1.1 19.4 10th 23.0 15.7 high 146%
Darwin NTC AWS 31.9   34.6 10th 24.5   21.6 30th
Delamere Weapons Range 36.7 +1.1 39.5 22nd 20.0 -0.8 13.8 17th 1.0 3.4 average 29%
Douglas River 38.0 +1.4 40.2 23rd 16.8 -1.9 11.7 2nd 5.0 4.4 high 114%
Dum In Mirrie AWS 31.6 -0.1 35.6 10th 21.8 -1.4 18.8 2nd 4.0 13.8 average 29%
Jabiru Airport 37.4 +1.2 39.8 27th 20.4 -1.2 16.0 20th 0.4 6.3 average 6%
Katherine Country Club 37.3   40.4 28th 18.5   12.5 17th 26.6
Mango Farm 37.1 +0.8 40.0 24th 16.7 -2.7 12.0 3rd 3.4 8.3 average 41%
McCluer Island 29.2 0.0 31.8 1st 24.5 -0.2 22.2 1st 0 0.3 v low 0%
Middle Point AWS 37.4 +1.2 38.8 24th 17.1 -2.2 13.7 3rd 39.2 19.9 high 197%
Noonamah AWS 37.5   39.3 24th 18.2   12.8 10th 24.8
Pirlangimpi 34.6 +1.5 36.8 23rd 20.8 -0.5 18.1 3rd 0.6 27.4 low 2%
Port Keats Aero 33.6 0.0 36.4 16th 19.5 -1.6 15.2 16th 0.6 3.0 average 20%
Arnhem (district 14BC)
Cape Wessel 31.5   32.3 25th 24.0   22.9 7th 0 6.9 lowest 0%
Gove Airport 30.8 +0.5 33.5 18th 18.7 -1.1 16.0 17th 0 5.8 lowest 0%
Groote Eylandt Airport AWS 32.8 +0.2 35.5 27th 17.8 0.0 14.3 19th 0.4 2.9 average 14%
Maningrida Aero 32.4   34.9 9th 19.9   16.2 3rd 0.2
Milingimbi AWS 31.7   34.3 9th 21.0   18.7 3rd 0 4.5 v low 0%
Ngayawili 31.9 +0.2 33.7 19th 20.2 -0.4 18.0 19th 1.0 7.3 high 14%
North East Island 29.4   31.9 27th 22.5   21.0 17th 2.6 0.8 high 325%
Warruwi 31.7 +0.8 33.9 17th 23.3 -0.3 20.2 1st 0 1.0 lowest 0%
Roper-Mcarthur (district 14DE)
Borroloola 35.9 +1.0 38.2 25th 17.4 -0.3 12.0 3rd 22.6 2.4 v high 942%
Bulman AWS 36.7   41.0 27th 15.7   11.0 2nd 35.8 3.8 v high 942%
Centre Island 31.1 +0.6 33.6 17th 22.1 -0.1 19.6 4th 1.2 1.4 average 86%
Daly Waters AWS 36.8 +2.2 40.9 27th 14.5 -2.5 7.6 17th 1.0 1.9 high 53%
McArthur River Mine 36.4 +1.2 39.3 27th 17.0 -0.2 10.5 3rd 21.8 5.3 v high 411%
Ngukurr AWS 36.5   40.2 27th 18.0   12.5 17th 13.2
Wollogorang 35.2 +0.8 38.6 26th 14.2 -1.7 9.5 17th 0 3.9 lowest 0%
Victoria (district 14F)
Lajamanu 35.7 +1.4 41.1 23rd 15.9 -0.7 8.3 16th 0 4.4 lowest 0%
Timber Creek 37.5 +1.0 40.3 25th 18.7 -1.9 11.8 4th 0 5.7 lowest 0%
Victoria River Downs 36.5 +1.0 40.3 23rd 14.8 -3.4 9.4 17th 0 4.2 lowest 0%
Wave Hill     36.8 13th 16.5 -1.4 10.2 10th 0 8.8 lowest 0%
Barkly (district 15A)
Elliott 36.1 +0.7 39.4 26th 16.3 -1.1 10.8 4th 7.8 6.0 high 130%
Tennant Creek Airport 32.9 +1.4 38.7 23rd 18.4 0.0 13.3 9th 8.8 7.9 average 111%
Alice Springs (district 15B)
Alice Springs Airport 29.6 +2.4 38.8 22nd 9.6 -0.7 1.0 1st 3.8 8.5 average 45%
Arltunga 28.1 +0.4 37.0 27th 9.4 -1.6 -0.4 10th 8.2 6.8 high 121%
Curtin Springs 29.5 +1.8 37.4 27th 10.2 +0.2 2.3 8th 3.4 10.0 average 34%
Jervois 30.3 +0.6 40.3 20th 11.6 +0.3 2.4 2nd 14.2 8.8 high 161%
Papunya 31.3 +0.2 37.5 27th 13.6   7.0 6th 6.8 7.2 high 94%
Rabbit Flat 35.3 +1.0 40.7 23rd 14.4 -0.1 6.0 10th 0 6.5 v low 0%
Territory Grape Farm 31.1 +0.9 38.2 27th 11.0 -1.0 4.7 9th 1.8 10.9 average 17%
Walungurru 32.9   39.0 27th 17.5   12.9 6th 1.8 10.0 high 18%
Yulara Aero 29.9 +1.3 38.0 27th 10.3 -0.4 1.0 6th 3.2 8.4 average 38%

Notes

A Monthly Climate Summary is prepared to list the main features of the weather in Northern Territory using the most timely and accurate information available on the date of publication; it will generally not be updated. Later information, including data that has had greater opportunity for quality control, will be presented in the Monthly Weather Review, usually published in the fourth week of the month.

This statement has been prepared based on information available at 5 pm on Monday 1 October 2012. Some checks have been made on the data, but it is possible that results will change as new information becomes available.

Averages are long-term means based on observations from all available years of record, which vary widely from site to site. They are not shown for sites with less than 10 years of record, as they cannot then be calculated reliably.
The median is sometimes more representative than the mean of long-term average rain.

The Rank indicates how rainfall this time compares with the climate record for the site, based on the decile ranking (very low rainfall is in decile 1, low in decile 2 or 3, average in decile 4 to 7, high in decile 8 or 9 and very high is in decile 10).
The Fraction of average shows how much rain has fallen this time as a percentage of the long-term mean.

Further information

Media
(03) 9669 4057
Enquiries