Wednesday, 2 January 2013 - Monthly Climate Summary for Western Australia - Product code IDCKGC11R0
Rainfall during December 2012 was above- to very-much-above-average through much of western WA, with areas of highest on record in the Southwest and Lower West districts due to extreme rainfall on the 11th and 12th that broke December and all-time records for some sites, as well as the record for the highest daily total in the Southwest Land Division (SWLD) for December. Several sites in the northeast Gascoyne and inland Pilbara also recorded their wettest December as a result of frequent thunderstorm activity during the month. In the remainder of the state, above- to very-much-above-average rainfall was observed in the Eucla and southern Southern Interior, and in the northern Northern Interior and inland Kimberley, while patches of below- to very-much-below-average rainfall were observed in the Southeast Coastal, Goldfields, eastern Interior, and north and west Kimberley.
Averaged across the state as a whole, rainfall during December 2012 was above-average, while for the Lower Southwest (southwest of a line from Jurien Bay to Bremer Bay) rainfall ranked as the sixth wettest December since comparable records commenced in 1900. For the wider SWLD, December 2012 rainfall was above-average.
A trough across northern WA and extending just off the west coast resulted in showers and thunderstorms on the 3rd and 4th over much of northern WA, extending into central parts and the northern SWLD. Severe thunderstorms were observed and Morawa Airport in the Central West registered a wind gust to 94 km/h on the 3rd, while Tenindewa in the Central West recorded 25.2 mm in the 24 hours to 9am on the 4th, which is the site's wettest December day in 11 years of record. Thunderstorms in the Pilbara produced heavy rainfall with 83.4 mm of rain recorded in the 24 hours to 9am on the 4th at Nullagine which produced minor flooding of the Nullagine River.
A deep surface trough across northern and western WA combined with a middle level disturbance to the west, brought showers and thunderstorms to much of northern and western WA on the 5th and 6th. In the 24 hours to 9am on the 6th, Wialki and Bonnie Rock, both in the Central Wheat Belt, observed their wettest December days in 80 and 75 years of record respectively with totals just below 40 mm. The wettest location in the state during the event was the Porongurups in the South Coastal district, which reported 49.0 mm, its wettest December day in 6 years of record.
A trough extending across northern WA and down the west coast resulted in showers and thunderstorms through much of northern and western WA on the 9th and 10th. Heavy rainfall was observed in parts of the Kimberley in the 24 hours to 9am on the 10th, while moderate to heavy totals were observed in the Central West and Central Wheat Belt. Bowgada in the Central West recorded 47.6 mm, which was its second wettest December day in 103 years of record, only behind 52.0 mm recorded on 9 December 1975, while Kondut in the Central Wheat Belt observed its wettest December day in 80 years of record with 43.0 mm. Severe thunderstorms produced strong winds at Dalwallinu in the Central Wheat Belt, with the site observing a maximum wind gust of 104 km/h, while Troughton Island in the Kimberley recorded a maximum wind gust of 91 km/h.
A deep surface trough interacted with a slow moving middle level low off the WA west coast to produce widespread showers and thunderstorms across most of WA from the 10th to 13th. The middle level low was both slow moving, allowing moisture to build up over southwest WA over a period of several days, and in phase with the surface trough, enhancing atmospheric instability. These factors combined to produce unusually heavy rainfall in southwest WA over several days. Very high rainfall totals were reported in the Lower West and Southwest districts on the 11th and 12th, but particularly in northern parts of the Southwest district, around the localities of Bunbury, Harvey, and Collie, with many sites registering December daily records and with some even surpassing their highest monthly total for December. Three daily rainfall reports during the event exceeded the previous highest daily rainfall recorded in the Southwest Land Division (SWLD) for December; a record that was broken in 2011 (i.e., just one year ago) after standing for more than 70 years. The heaviest rainfall was reported during the 24 hours to 9am on the 13th with the highest fall being 210.8 mm at Yourdamung Lake, northeast of Collie in the Southwest district. This is the fifth highest daily rainfall total on record in the SWLD for any month. Please refer to Special Climate Statement 42 for further information. The surface trough and middle level feature responsible for the heavy rainfall moved eastward into central parts of the state on the 13th and 14th, with showers and thunderstorms observed throughout much of southern WA and moderate daily totals reported in the Central Wheat Belt and Eucla, while showers and thunderstorms were observed over much of central and northern WA, with moderate to heavy falls observed in the Kimberley, Pilbara, and north Gascoyne.
Seasonal showers and thunderstorms were a regular feature over northern WA during December 2012, with numerous sites observing daily falls of over 50 mm and several sites in the northeast Gascoyne and inland Pilbara, including Millstream with 111 years of record, observed their wettest December on record. Outside of the extreme rainfall in the Southwest District on the 11th and 12th, the heaviest falls in WA during December 2012 were in the Kimberley where Liveringa Station observed 106.0 mm in the 24 hours to 9am on the 12th, and Mount Hart Station observed 87.0 mm in the 24 hours to 9am on the 16th.
Maximum temperatures during December 2012 were well above average throughout much of western and southern WA, and in the north and west Kimberley with daytime temperatures up to 2 °C above normal in most of southern WA, grading to up to 3 °C along parts of the west and south coast, and up to 4 °C above normal the west Eucla and in the west Kimberley near Broome. In contrast, below average maxima were observed through parts of inland northern WA, with daytime temperatures up to 3 °C below normal through inland Pilbara, northwest Gascoyne and southeast Kimberley. Broome in the west Kimberley observed its hottest December in 73 years of record, with a mean maximum temperature of 36.3 °C.
When averaged across the state as a whole, the mean maximum temperature for December 2012 was above-average, continuing the run since April of consecutive mean maxima above the average. After a reasonably cool first half of December 2012, very hot conditions in the Lower Southwest (southwest of a line from Jurien Bay to Bremer Bay) towards the end of the month resulted in the region observing its sixth hottest December since comparable records commenced in 1950.
A trough across northern WA resulted in hot conditions across northern WA to begin December 2012, with temperatures reaching the low to mid-forties in the Pilbara on the 1st and 2nd. Marble Bar was the hottest location with 45.3 °C. The hot conditions shifted to western WA on the 3rd, with sites in the Central West, Gascoyne and adjacent Pilbara observing maxima in the high thirties to low forties. Geraldton Airport was the hottest location, reaching a maximum of 43.1 °C at 1321 WST, before thunderstorms moved through the area at approximately 1500 WST and temperatures rapidly dropped to the low twenties by 1530 WST. A relatively hot day was observed in western and southern parts of the SWLD on the 4th, with a trough located near the west coast. Conditions were particularly hot in western parts of the Lower West where temperatures were in the mid-to-high thirties, 8 °C to 10 °C above the December average. In contrast, showers and thunderstorms in the Gascoyne resulted in Murchison recording a maximum temperature of 27.9 °C, well below the December mean of 37.3 °C. Perth Metro reached a maximum of 38.2 °C on the 4th, the hottest location in southern WA. A trough across northern WA resulted in very hot day-time maxima on the 9th, with temperatures reaching the mid-forties in the Kimberley. Bidyadanga observed the highest temperature in the state with 45.3 °C, the site's fourth hottest December day on record. West Roebuck's maximum of 45.0 °C was that site's hottest day in December since records commenced in 1999, breaking the previous record of 44.9 °C set on 1 December 2009.
The lowest maximum temperature of the month in WA was recorded at Mt Barker on the 12th as a low pressure system over the SWLD brought showers, thunderstorms and cloud to the region. Southeasterly winds along with cloud and precipitation kept the maximum at the site to just 16.6 °C.
Northerly winds brought hot conditions to the southern Goldfields, Southeast Coastal, and Eucla on the 17th, with temperatures reaching 40 °C at some locations. A broad trough across inland northern WA resulted in hot conditions in parts of the Pilbara, Gascoyne and Interior on the 19th through to the 23rd, extending into the southeastern SWLD on the 21st and Eucla on the 22nd, with temperatures reaching the mid-forties in the inland Pilbara and northwest Gascoyne. Emu Creek recorded a maximum of 47.3 °C on the 23rd, the highest temperature in WA in December 2012, while Learmonth Airport recording 46.6 °C on the same day which was the second hottest day of the month in WA. A prolonged spell of hot weather was observed in southwestern WA from Christmas Day through to the end of the month, with the hot weather extending across southern WA on the 31st. The hot conditions were due to a stangnant weather system consisting of a high in the Bight and a trough near the west coast directing generally hot easterly winds over the area with little relief from the seabreeze. Particularly hot conditions were observed on the 30th in the Southwest District, with Cape Naturaliste observing 37.7 °C, its hottest December day in 56 years of record, while Jarrahwood observed 40.5 °C which is an equal record for December. Busselton Aero observed 41.0 °C, its hottest day in 15 years of record, breaking the annual record of 40.2 °C set on 26 January 2012, while Witchcliffe's 40.6 °C equalled their annual record set on 26 January 2012 in 13 years of record.
Minimum temperatures during December 2012 were above- to very-much-above-average across most of the State, with areas of highest on record in the west Pilbara, east Pilbara and adjacent west Kimberley. Overnight temperatures were up to 2 °C warmer than normal across much of the state, with patches of up to 3 °C above average across central and northwestern parts and a small area of up to 4 °C above normal in the far west Pilbara. In contrast, temperatures were below- to very-much-below-average in the remaining Kimberley and northeastern Northern Interior with an area of up to 2 °C below average in the southwest Kimberley and northeastern Northern Interior. A number of sites in the Pilbara observed their warmest December on record, with several daily December records broken. Particularly high minima were observed on the 29th and 30th in the Lower West and Southwest with several sites breaking December records.
When averaged across WA as a whole, the mean minimum temperature during December 2012 was well above average and ranked as the third warmest December on record. The Lower Southwest (southwest of a line from Jurien Bay to Bremer Bay) also saw well above normal overnight minima, with the region observing its fourth warmest December, continuing a run of above average monthly mean minima in which only two months since November 2010 have recorded below average overnight temperatures (May 2012 and July 2012). Comparable temperature records commenced in 1950.
A ridge developed along the south coast to begin December 2012, resulting in cool mornings over much of southern WA from the 1st to 3rd. WA's coolest temperature for December 2012 occurred on the 1st, with Wandering in the Great Southern observing a minimum of just 3.8 °C. A warm morning was observed in southern parts of the SWLD on the 5th, with minimum temperatures in the Great Southern and Central Wheat Belt in the low twenties, well above the December average, which is generally in the low to mid-teens. Warm conditions were observed in northern WA on the 9th and 10th, with temperatures in the high-twenties to low-thirties at some locations in the Pilbara and Kimberley. Fitzroy Crossing Aerodrome recorded a minimum temperature of 31.1 °C on the 9th, which was its second highest December minimum since records commenced in 1997, only behind a minimum of 32.1 °C on 15 December 2009. Mandora observed the highest minimum temperature in the state on the 10th with 30.7 °C, which was its second hottest night in December in 47 years of record, and its hottest night since its December record was set at 32.4 °C on 12 December 1993. Warm minima were experienced in northern parts of WA on the morning of the 24th, with minimum temperatures in the Pilbara and Kimberley in the high twenties to low thirties. Emu Creek Station observed its warmest December night in 40 years of record with 32.7 °C which was also the warmest night in December 2012. Learmonth also observed their warmest December minimum with 29.2 °C. The warm overnight conditions continued through much of central and southwestern WA through to the end of the month, complimenting the hot daytime temperatures. Particularly warm minima were observed on the 29th in the Lower West and Southwest districts, where Perth Airport and Karnet observed their warmest December minima in 59 and 47 years of record respectively, while the 24.3 °C at Cape Naturaliste on the 30th was their equal highest December minima in 56 years of record.
Tropical cyclone Mitchell formed out of a low well to the northwest of the Pilbara coast during the morning of the 29th. Mitchell moved in a generally south-southwest direction, remaining off the coast and weakening below cyclone strength during the morning of the 30th. Mitchell was a category 1 system and the first tropical cyclone for the Western Region in the 2012/13 season.
|Extremes in December 2012|
|Hottest day||47.3 °C at Emu Creek Station on the 23rd|
|Warmest days on average||40.7 °C at Marble Bar|
|Coolest days on average||22.3 °C at Albany|
|Coldest day||16.6 °C at Mount Barker on the 12th|
|Coldest night||3.8 °C at Wandering on the 1st|
|Coolest nights on average||12.3 °C at Jacup|
|Warmest nights on average||27.3 °C at Broome Airport|
|Warmest night||32.7 °C at Emu Creek Station on the 24th|
|Wettest overall||258.6 mm at Mount Hart Station|
|Wettest day||210.8 mm at Yourdamung Lake on the 13th|
|Highest wind gust||104 km/h at Dalwallinu on the 9th|
|Record highest December daily rainfall|
| Highest daily rainfall
in December 2012 (mm)
| Previous wettest
|Collie||157.2||on the 13th||42.0||on the 24th in 1987||106|
|Wilgarrup||48.2||on the 11th||47.0||on the 25th in 1925||106|
|Brunswick Junction||77.6||on the 12th||33.1||on the 28th in 1984||104|
|Boyanup||68.8||on the 13th||45.0||on the 4th in 2001||102|
|Wialki||39.0||on the 6th||35.1||on the 7th in 1958||80|
|Kondut||43.0||on the 10th||40.2||on the 17th in 2007||78|
|Bonnie Rock||38.0||on the 6th||35.6||on the 19th in 1978||75|
|Roelands||75.2||on the 12th||37.8||on the 31st in 1959||71|
|Ferguson Valley||87.0||on the 13th||33.0||on the 4th in 2001||41|
|Medina Research Centre||35.6||on the 12th||26.8||on the 13th in 2011||30|
|Record highest total December rainfall|
| Total rainfall
for December 2012 (mm)
| Previous wettest
|Brunswick Junction||100.4||64.3||in 1944||104||15.6|
|Turee Creek||133.0||130.3||in 1975||88||23.9|
|Neds Creek||77.8||72.6||in 1995||66||17.0|
|Ferguson Valley||142.8||68.4||in 2001||41||17.9|
|Mosman Park||41.2||33.9||in 1991||35||6.6|
|Medina Research Centre||56.2||51.8||in 2011||30||12.1|
|Record highest December temperature|
in December 2012 (°C)
|Cape Naturaliste||37.7||on the 30th||37.6||on the 26th in 2007||56||23.6|
|Jarrahwood||40.5||on the 30th||= 40.5||on the 26th in 2007||30||26.9|
|Record highest December mean daily maximum temperature|
Mean daily maximum
for December 2012 (°C)
|Broome Airport||36.3||36.0||in 1951||73||33.8|
|Record highest December daily minimum temperature|
Highest daily minimum
in December 2012 (°C)
|Perth Airport||27.5||on the 29th||26.9||on the 24th in 1960||69||14.9|
|Cape Naturaliste||24.3||on the 30th||= 24.3||on the 26th in 2007||56||13.9|
|Bidyadanga||30.0||on the 9th||29.6||on the 24th in 2006||54||25.7|
|Karnet||23.5||on the 29th||22.6||on the 29th in 2009||47||13.4|
|Emu Creek Station||32.7||on the 24th||32.3||on the 21st in 2004||41||22.3|
|Learmonth Airport||29.2||on the 24th||27.6||on the 30th in 1994||38||20.8|
|Record highest December mean daily minimum temperature|
Mean daily minimum
for December 2012 (°C)
|Port Hedland Airport||26.6||26.1||in 1962||64||24.0|
|Bidyadanga||27.1||= 27.1||in 2002||53||25.7|
|Onslow Airport||25.3||24.7||in 1973||46||22.2|
|Narembeen||16.8||= 16.8||in 1977||44||14.4|
|Emu Creek Station||24.8||24.7||in 1979||40||22.3|
|Telfer Aero||26.9||26.7||in 2003||38||25.3|
|Learmonth Airport||23.3||23.0||in 2010||37||20.8|
|Summary statistics for December 2012|
|North Kimberley (district 01)|
|East Kimberley (district 02)|
|Halls Creek Airport||37.5||-0.3||43.5||8th||24.2||-0.5||20.4||19th||83.0||82.2||average||101%|
|West Kimberley (district 03)|
|Fitzroy Crossing Aero||39.7||+0.6||45.0||8th||25.6||-0.1||22.0||22nd||130.6||122.6||average||107%|
|De Grey (district 04)|
|Port Hedland Airport||37.6||+1.0||42.7||10th||26.6||+2.6||19.7||1st||0.2||17.9||average||1%|
|Fortescue (district 05)|
|Barrow Island Airport||34.4||+2.4||38.8||24th||26.2||+1.9||23.4||2nd||53.2||6.6||v high||806%|
|West Gascoyne (district 06)|
|Carnarvon Airport||30.6||+1.3||39.9||28th||21.8||+1.2||16.9||1st||14.4||5.7||v high||253%|
|Emu Creek Station||40.1||+0.3||47.3||23rd||24.8||+2.5||19.0||1st||20.5||13.3||high||154%|
|Shark Bay Airport||32.9||+0.8||39.2||29th||20.5||+0.9||15.4||1st||13.6||12.9||high||105%|
|East Gascoyne (district 07)|
|Newman Aero||36.9||-2.1||44.4||24th||23.7||-0.1||18.9||6th||81.0||38.0||v high||213%|
|Murchison (district 07A)|
|Meekatharra Airport||35.8||-0.6||42.8||24th||22.7||+0.7||15.7||1st||78.2||14.5||v high||539%|
|Mount Magnet Aero||36.6||+1.2||44.1||21st||22.3||+1.3||13.5||1st||28.4||24.6||average||115%|
|North Coast (district 08)|
|Geraldton Airport Comparison||32.5||+3.0||42.8||3rd||17.8||+1.5||9.3||1st|
|Morawa Airport||35.3||+0.2||43.7||26th||18.9||+1.6||9.2||1st||56.8||16.3||v high||348%|
|Central Coast (district 09)|
|Badgingarra Research Stn||32.9||+0.9||41.8||26th||16.7||+1.7||7.1||1st|
|Garden Island HSF||27.0||+1.6||36.6||30th||18.5||+1.4||13.2||1st||52.0||13.3||v high||391%|
|Gingin Aero||31.7||+1.2||41.5||31st||15.8||+1.5||7.8||1st||57.6||10.8||v high||533%|
|Jandakot Aero||30.7||+1.8||41.2||31st||16.4||+1.8||6.6||8th||28.8||11.0||v high||262%|
|Jurien Bay||30.6||+2.5||42.0||31st||16.7||+1.1||9.0||8th||23.8||7.2||v high||331%|
|Pearce RAAF||32.7||+2.5||42.7||31st||16.4||+1.9||6.7||1st||42.8||10.8||v high||396%|
|Perth Metro*||31.2||+2.3||42.1||31st||17.8||+1.5||9.4||8th||20.2||13.3||v high||151%|
|Rottnest Island||26.8||+1.8||37.5||31st||18.8||+1.3||14.4||1st||27.6||8.2||v high||337%|
|South Coast (district 09A)|
|Albany Airport Comparison||24.5||+1.4||33.1||30th||13.4||+0.9||7.1||9th||41.6||27.8||high||150%|
|Collie East||29.3||+1.0||39.4||30th||13.1||+1.6||4.5||1st||155.0||26.9||v high||576%|
|North Central (district 10)|
|South Central (district 10A)|
|Newdegate Research Station||31.4||+2.3||40.8||21st||13.5||+1.8||4.2||1st||11.6||15.2||average||76%|
|Eucla (district 11)|
|Red Rocks Point||25.1||+1.1||39.2||22nd||16.8||+0.5||9.0||2nd||43.8||20.6||high||213%|
|South East (district 12)|
|Salmon Gums Res.Stn.||30.8||+1.9||41.3||31st||13.2||+1.0||5.1||2nd||9.6||20.1||average||48%|
|Southern Cross Airfield||34.2||+1.6||43.8||21st||17.6||+2.4||9.7||1st||21.6||17.6||high||123%|
|North East (district 13)|
|Giles Meteorological Office||36.4||+0.7||43.8||24th||23.1||+1.3||17.9||10th||36.8||45.1||average||82%|
|Offshore Islands (district 200)|
|Christmas Island Aero||28.5||+0.8||30.6||28th|
|Cocos Island Airport||29.3||-0.1||30.4||31st||25.4||+0.8||23.3||5th||125.2||115.6||high||108%|
A Monthly Climate Summary is prepared to list the main features of the weather in Western Australia 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 9 am on Wednesday 2 January 2013. 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.
The median is sometimes more representative than the mean of long-term average rain.
*Official Perth observations have been recorded at several different sites with varying instrumentation over the years, and these changes can affect the continuity of the climate record. For the current Mt Lawley site, the most significant changes of this kind relate to minimum temperature and rain days.
For that reason, current mean temperature and rain-day data quoted here are based only on readings from the Mt Lawley site, which commenced observations in 1993. Sunshine recordings are from Perth Airport and for similar reasons current means use only Perth Airport data, which commenced in 1993.
The Rank indicates how rainfall this time compares with the climate record for the site,
based on the
(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.