Northern Territory in April 2011: Early start to the dry season

April began with heavy rains and gusty storms across the Top End with several stations exceeding their previous record April rainfall within the first week of the month. The following weeks showed signs of the approaching dry season with cooler nights and fewer storms.

Heavy rainfall at Katherine

On the 2nd, Katherine Aviation museum measured 83.2 mm which was the wettest April day on record, passing the previous record of 64.0 mm set on the 25th in 1970. Katherine Aviation Museum then broke this record again on the 5th when they received 88.4 mm. The average April total rainfall at Katherine is only 38.4 mm.

Eastern Arnhem thunderstorms

On the 12th, a series of thunderstorms dumped heavy rain over the eastern Arnhem District. Rainfall totals from the event include 149.0 mm of rainfall at Gove Airport and 148.0 mm of rainfall at Yirrkala Tropical Gardens.

A taste of the dry season

The official start of the dry season is 1 May, but the end of April gave a taste of the dry season to Territorians in the Top End. On the 20th and 21st the minimum temperature at Darwin Airport dipped to below 20 °C for the first time this year. Another dry season indicator happened on the 18th when, for the first time this year, the dew point temperature in Darwin dropped below 15 °C.

Rainfall

A low pressure system over the Joseph Bonaparte Gulf on the 1st and 2nd pushed warm, moist, tropical air inland which produced heavy rainfall and gusty storms across the western Top End. As the low moved southwest the axis of the monsoon trough also moved south, bringing another burst of heavy rain to the area. This heavy rainfall during the first week of the month set new daily and monthly rainfall records for many stations across the western Top End.

The rest of the month showed signs of transition from wet season to dry season. Occasional isolated thunderstorms brought heavy rains to the Top End including Arnhem and coastal regions. As the month progressed these storms became less frequent.

The wettest single day was on the 12th when 149.0 mm fell at Gove Airport and 148.0 mm fell at Yirrkala Tropical Gardens. The next wettest day was at Mango Farm with 132.2 mm on the 1st.

The wettest overall was Yirrkala Tropical Gardens with 563.0 mm, followed by North East Island with 552.0 mm, and then Gove Airport with 491.8 mm.

Temperature

Mean daily maximum temperatures were below average across the NT while the mean daily minimum temperatures were near average in the Top End and below average across the rest of the NT. Thick cloud cover in the beginning of the month kept daily maximum temperatures low while allowing minimum temperatures to stay relatively high across the Top End. The rest of the Territory, especially the Alice Springs District was strongly influenced by a series of high pressure systems in the Bight that pushed cool dry air into the Territory from the southeast.

The warmest on average was Jabiru Airport with 28.3 °C followed by Dum In Mirrie with 28.2 °C. The coolest on average was Arltunga with 18.1 °C, followed by Alice Springs Airport with 18.3 °C, and then Yulara Aero with 20.5 °C.

Maximum temperature

The hottest day was at Bradshaw with 35.6 °C on the 22nd, followed by McArthur River Mine with 35.5 °C on the 22nd, and Port Keats Aero also with 35.5 °C on the 26th.

The warmest days on average were at Jabiru Airport with 33.1 °C followed by McArthur River Mine and Bradshaw with with 33.0 °C, and then Port Keats Aero with 32.9 °C.

The coolest days on average were at Arltunga with 26.1 °C, followed by Alice Springs Airport with 27.0 °C, and then Kulgera with 27.5 °C.

The coldest day was at Rabbit Flat with 21.0 °C on the 4th, followed by Arltunga with 22.0 °C on the 11th, and then Tennant Creek Airport with 22.3 °C on the 2nd.

Some sites, including Katherine Aviation Museum and Victoria River Downs, had their lowest April mean daily maximum temperature on record.

Minimum temperature

The coldest nights were at Arltunga with 2.0 °C on the 12th, 3.8 °C on the 25th, and 4.4 °C on the 19th.

The coolest nights on average were at Alice Springs Airport with 9.7 °C, followed by Arltunga with 10.1 °C, and then Kulgera with 10.8 °C.

The warmest nights on average were at North East Island with 25.4 °C followed by Centre Island with 24.3 °C and Warruwi also with 24.3 °C.

The warmest night was at Point Stuart with 27.2 °C on the 8th.

Tennant Creek Airport, Centre Island and Lajamanu had their lowest April mean daily minimum temperature on record.

Wind

The strongest wind gusts were at Point Fawcett and at Walungurru which both measured 65 km/h on the 2nd. The next strongest wind gusts were Walungurru with 63 km/h on the 1st and Centre Island which also measured a gust of 63 km/h on the 2nd.

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Extremes in April 2011
Hottest day 35.6 °C at Bradshaw on the 22nd
Warmest days on average 33.1 °C at Jabiru Airport
Coolest days on average 26.1 °C at Arltunga
Coldest day 21.0 °C at Rabbit Flat on the 4th
Coldest night 2.0 °C at Arltunga on the 12th
Coolest nights on average 9.7 °C at Alice Springs Airport
Warmest nights on average 25.4 °C at North East Island
Warmest night 27.2 °C at Point Stuart on the 8th
Warmest on average overall 28.2 °C at Jabiru Airport
Coolest on average overall 18.1 °C at Arltunga
Wettest overall 565.0 mm at Yirrkala Tropical Gardens
Wettest day 149.0 mm at Gove Airport on the 12th
Highest wind gust 65 km/h at Point Fawcett on the 2nd
65 km/h at Walungurru on the 2nd

Record highest April daily rainfall
Highest daily rainfall
in April 2011 (mm)
Previous wettest
for April
Years of
record
Katherine Aviation Museum 88.4 on the 5th 64.0 on the 25th in 1970 35
Hidden Valley 61.5 on the 3rd 32.8 on the 27th in 2006 26
Gorrie 107.0 on the 6th 55.6 on the 9th in 1996 23
Wagait Beach 114.6 on the 1st 90.0 on the 5th in 2006 21
Walker Creek 107.6 on the 1st 84.0 on the 15th in 2010 17

Record highest total April rainfall
Total rainfall
for April 2011 (mm)
Previous wettest
for April
Years of
record
Average for
April
Katherine Aviation Museum 227.8 212.6 in 2006 35 38.4
Hidden Valley 135.7 99.6 in 2006 28 17.5
Mango Farm 356.8 308.6 in 2006 30 60.0
Gorrie 185.0 92.6 in 2006 24 19.3
Litchfield 354.0 179.0 in 1985 21 60.5



Record lowest April mean daily maximum temperature
Mean daily maximum
temperature
for April 2011 (°C)
Previous coolest
for April
Years of
record
Average for
April
Victoria River Downs 31.5 32.0 in 1983 42 34.5
Daly Waters 30.7 30.9 in 1963 41 33.9
Centre Island 30.1 = 30.1 in 1999 36 32.1
Timber Creek 32.7 32.8 in 1985 30 35.2
Katherine Aviation Museum 31.4 31.6 in 2006 24 34.2
Lajamanu 30.2 30.4 in 1971 17 33.8
Kidman Springs 32.0 33.1 in 2006 15 35.5
Delamere Weapons Range 31.0 31.6 in 2006 13 34.3
Rabbit Flat 30.5 31.0 in 2000 13 34.2





Record lowest April mean daily minimum temperature
Mean daily minimum
temperature
for April 2011 (°C)
Previous coolest
for April
Years of
record
Average for
April
Tennant Creek Airport 17.5 18.2 in 1971 41 20.4
Centre Island 24.3 24.5 in 2008 36 25.3
Lajamanu 15.4 15.5 in 2008 17 18.0



Summary statistics for April 2011
Maximum temperatures
for April
(°C)
Minimum temperatures
for April
(°C)
Rainfall
for April
(millimetres)
Mean Diff
from
average
Highest Mean Diff
from
average
Lowest Total Average
Rank Fraction of
average
Darwin-Daly (district 14GA)
Batchelor Aero 31.9 -2.0 33.8 22nd 22.1 +0.6 15.1 20th 353.8 88.7 v high 399%
Bradshaw 33.0   35.6 22nd 21.5   15.5 19th 115.8
Channel Point 31.3 -1.1 32.7 10th 23.2 -0.2 18.4 20th 268.9 111.0 high 242%
Darwin Airport 31.7 -1.0 33.3 25th 23.3 -0.7 19.1 21st 201.4 99.8 high 202%
Delamere Weapons Range 31.0 -3.3 33.3 8th 20.3 -0.7 15.7 30th 54.6 18.8 v high 290%
Douglas River 32.4 -2.3 34.1 10th 21.0 +0.7 13.9 20th 209.6 47.2 v high 444%
Dum In Mirrie 32.3 -0.6 34.8 23rd 23.7 -0.6 19.3 20th 240.8 96.9 high 249%
Jabiru Airport 33.1 -1.4 35.3 22nd 23.2 -0.3 19.7 28th 196.4 76.5 v high 257%
Katherine Aviation Museum 31.4 -2.8 33.1 22nd 20.1 -0.6 13.7 20th 227.8 38.4 highest 593%
Mango Farm 32.3 -2.1 34.5 24th 22.3 +0.8 16.8 20th 356.8 60.0 highest 595%
Middle Point 32.7   34.8 25th 22.3   16.3 20th 297.8
Noonamah 32.7   34.5 22nd 22.2   16.9 20th 163.8
Pine Creek Council 31.4 -2.6 33.4 22nd 21.4 -0.7 17.2 19th 295.6 69.4 v high 426%
Pirlangimpi 32.1 -0.6 33.8 25th 23.0 0.0 19.3 21st 424.2 149.0 v high 285%
Point Fawcett 31.1 -1.1 33.0 23rd 22.6 -1.0 16.5 21st 339.8 118.0 v high 288%
Port Keats Aero 32.9   35.5 26th 22.5   15.3 20th 242.4
Tindal RAAF 32.2 -1.6 34.1 15th 20.3 -0.2 14.3 20th 96.6 36.2 high 267%
Arnhem (district 14BC)
Alyangula Police 30.7 -1.1 32.5 26th 21.9 -1.0 18.1 19th 304.5 180.2 high 169%
Gove Airport 29.8 -1.0 31.5 22nd 23.3 +0.1 20.3 19th 492.4 223.4 high 220%
Groote Eylandt Airport 31.3 -1.1 33.3 22nd 21.4 -0.1 16.1 19th 268.4 162.1 high 166%
Maningrida Aero 31.7   34.1 26th 23.3   21.0 20th 350.8
Milingimbi 31.7   34.2 24th 23.5   20.1 19th 403.2
Ngayawili 30.9 -0.8 32.4 29th 23.8 +0.3 22.1 29th 189.6 192.3 high 99%
North East Island 30.3   31.9 25th 25.4   23.4 5th 552.0 173.7 high 318%
Warruwi 30.5 -1.1 32.3 26th 24.3 -0.7 22.3 20th 97.6 120.1 average 81%
Roper-Mcarthur (district 14DE)
Borroloola 32.4 -1.5 34.6 22nd 18.7 -1.6 13.5 19th 229.8 55.9 v high 411%
Bulman 31.7   34.0 15th 21.0   15.6 19th 133.6
Centre Island 30.1 -2.0 32.5 22nd 24.3 -1.0 21.9 19th 233.8 85.4 v high 274%
Daly Waters 30.7 -3.2 33.1 8th 17.9 -1.8 11.7 20th 107.6 20.7 v high 520%
Larrimah 31.4 -2.5 33.5 25th 19.1 -0.7 12.0 19th 80.0 31.7 v high 252%
McArthur River Mine 33.0 -1.8 35.5 22nd 20.1 -0.4 14.9 19th 79.4 28.1 v high 283%
Ngukurr 31.8 -2.3 33.9 22nd 22.0 +0.1 17.2 19th 97.2 54.9 high 177%
Wollogorang 31.6 -2.2 34.5 21st 18.3 -1.4 12.8 19th 20.5 38.1 average 54%
Victoria (district 14F)
Kidman Springs 32.0 -3.5 34.7 15th 19.3 -1.3 12.4 19th 64.3 23.1 v high 278%
Lajamanu 30.2 -3.6 33.4 15th 15.4 -2.6 9.7 19th 49.0 13.8 v high 355%
Timber Creek 32.7 -2.5 35.0 15th 20.6 -0.5 13.8 19th 69.1 29.9 high 231%
Victoria River Downs 31.5 -3.0 35.8 26th 18.6 -1.1 11.9 19th 97.4 22.5 v high 433%
Wave Hill 30.8 -3.5 33.8 8th 16.9 -1.9 10.6 19th 30.4 18.7 high 163%
Barkly (district 15A)
Brunette Downs 30.0 -3.6 33.1 9th 17.2 -2.0 13.0 18th 37.4 14.5 v high 258%
Tennant Creek Airport 28.7 -3.0 32.1 14th 17.5 -2.9 13.2 18th 20.2 15.4 high 131%
Alice Springs (district 15B)
Alice Springs Airport 27.0 -1.2 31.6 14th 9.7 -2.9 5.1 12th 0 16.3 lowest 0%
Arltunga 26.1   32.0 14th 10.1   2.0 12th 0 16.0 lowest 0%
Curtin Springs 28.9 -0.2 33.6 13th 12.5 -0.9 8.0 11th 0 15.5 lowest 0%
Jervois 28.7 -1.9 34.2 14th 13.0 -1.2 5.8 12th 0 17.1 lowest 0%
Kulgera 27.5 -0.4 33.1 13th 10.8 -3.0 4.5 11th 0.4 13.9 average 3%
Rabbit Flat 30.5 -3.7 35.0 15th 14.8 -1.8 9.2 24th 13.4 22.0 high 61%
Territory Grape Farm 29.0 -1.8 33.2 14th 12.2 -2.4 7.2 13th 0 17.9 lowest 0%
Walungurru 31.5   34.7 9th 18.9   15.6 19th 0
Yuendumu 28.5 -1.6 32.7 14th 13.7 -1.8 10.3 17th 0 22.8 lowest 0%
Yulara Aero 28.6 -1.3 33.1 13th 12.6 -1.8 7.1 18th 0 13.3 lowest 0%
Offshore Islands (district 200)
Northern Endeavour 32.2 -0.7 35.0 20th 26.9 -0.6 23.0 17th

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 12 pm on Tuesday 3 May 2011. 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 the years 1800 to 2009. They are not shown for sites with less than 10 years of record in that time, 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

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