Tuesday, 2 October 2012 - Monthly Climate Summary for Western Australia - Product code IDCKGC11R0
Western Australia in September 2012: A very warm month
- Rainfall: near average for WA
- Maximum temperature: 4th highest for WA; above average for southwest WA
- Minimum temperature: above average for WA; near average for southwest WA
Rainfall in western parts of the Southwest Land Division (SWLD) was near average to above average during September 2012, with some small areas of very much above average rainfall. In contrast, below to very much below average rainfall was observed in much of southeastern and central WA (see the maps below). For the remainder of the state, rainfall was a mixture of above and below average, although rainfall totals are typically low in northern WA during September.
Averaged across WA, September rainfall was near average. After the 6th driest winter on record in the Lower Southwest (southwest of a line from Jurien Bay to Bremer Bay), rainfall during September was near normal when averaged across the region. Parts of the region reported above average September rainfall, and Wokalup in the Southwest and Walpole in the South Coastal observed their wettest September on record, whilst sites in western parts of the Great Southern registered their wettest September for over 30 years.
A strong cold front moved through western parts of WA on the 3rd and into central parts of the state during the morning of the 4th, with widespread moderate rainfall observed through the western SWLD, and lighter falls extending into eastern parts of the SWLD, Gascoyne, west Pilbara, and Goldfields. Heavy rainfall in the 40 to 70 mm range was observed at a number of locations in the Southwest and Lower West districts in the 24 hours to 9am on the 4th. Bickley recorded the highest daily total with 67.2 mm, which is the 4th highest September daily total for the site in 44 years of record, and the highest daily total in WA for September 2012. Strong winds were observed in parts of the SWLD with the passage of the front during the afternoon and evening of the 3rd, particularly along the Lower West coast where gusts of over 90 km/h were recorded. Strong winds continued in the wake of the front around the Southwest Capes on the 4th, with Cape Naturaliste and Cape Leeuwin observing wind gusts of 117 km/h and 115 km/h respectively and moderate rainfall totals were observed in western and southern parts of the SWLD after very heavy rainfall the previous day. Reports of snow on Bluff Knoll in the Stirling Ranges were also received on the 4th. A strong cold front on the 21st brought moderate to heavy rainfall to the Lower West, Southwest, and South Coastal districts and strong gusts to the Southwest Capes, with Cape Leeuwin observing winds to 115 km/h. An unstable westerly flow lay over southwestern WA on the 26th and a cold front crossing the area during the afternoon and overnight resulted in moderate to heavy falls in the 24 hours to 9am on the 27th in the Southwest, Lower West, and South Coastal districts. Showers and thunderstorms on the last day of September 2012 brought moderate to heavy rainfall to the northern Interior, inland Kimberley and inland east Pilbara.
Despite the near average September, the Lower Southwest has recorded its 8th driest January to September period on record, largely as a result of registering its 8th driest autumn, and 6th driest winter, which included the driest July on record since comparable records commenced in 1900.
Maximum temperatures during September were above to very much above average throughout almost all of WA with areas of highest on record in eastern and northern parts of the state. Eastern parts of the Eucla, parts of the Interior, and western parts of the Kimberley saw mean maximum temperatures up to 4 °C warmer than normal, and Eucla and Eyre, both in the Eucla district, observed their equal warmest and warmest September on record respectively. Esperance, in the neighbouring South Coastal, and Warburton, in the Interior, observed their 3rd warmest Septembers in 43 and 38 years of record respectively.
When averaged across the state as a whole, the mean maximum temperature during September 2012 ranked as 4th highest on record for WA, continuing a run since April of six consecutive above average months. Mean maximum temperatures were also above average in the Lower Southwest (southwest of a line from Jurien Bay to Bremer Bay) and September 2012 continued the very warm year to date in the region. Almost all months so far in 2012, apart from February, have seen above average mean maxima in the Lower Southwest, with the mean maximum for January to September 2012 being 0.9 °C above normal and ranking equal 3rd highest since comparable temperature records commenced in 1950. The very much above average year so far is largely due to an above average January, a very much above average autumn (5th warmest), and an above average July to September. The run of "warm" temperatures has persisted for three years as the Lower Southwest has only recorded two months below the average, in terms of mean maximum temperature, since October 2009.
A very hot day was observed over the SWLD on the 9th as a high over southeast Australia and a trough off the west coast directed northerly winds over the area. Temperatures were in the low twenties in southwestern parts of the division, grading to the high twenties in central and eastern parts, and into the low thirties in the Central West. The hot conditions moved over central and southern parts of the state on the 10th in northerly winds ahead of a cold front, with particularly hot temperatures for September observed in the Southeast Coastal, southern Goldfields, and western Eucla, where temperatures were in the high twenties to low thirties. Temperatures reached the low forties in the Kimberley on the 13th and 14th, then again from the 23rd through to the 28th. Kununurra Aerodrome in the Kimberley registered its hottest September day in 27 years of record with 41.1 °C on the 24th breaking the previous record of 41.0 °C set on 25 September 1989, while Argyle Aerodrome in the Kimberley observed its hottest September temperature in 19 years of record twice, with 40.7 °C on the 27th followed by 40.8 °C on the 28th, both breaking the previous record of 40.5 °C set on 30 September 1998.
A cool, cloudy, and showery day across western and central parts of WA on the 4th saw unusually low maximum temperatures recorded. Brookton in the Great Southern recorded a maximum temperature of 10.6 °C, its equal coolest September day in 45 years of record, equal with a maximum of 10.6 °C recorded on 22 September 1968, while Mount Barker in the South Coastal observed the coldest day in WA during September 2012 with a maximum of just 9.8 °C. Another very cold day was observed in the southwest of the state in the wake of a cold front on the 27th, with Karnet in the Lower West recording a maximum of 9.9 °C and most other sites in the area only reaching the low teens.
Below to very much below average minimum temperatures were observed in the northern Kimberley during September 2012, contrasting with above to very much above average overnight temperatures for much of the remainder of the state. Minimum temperatures were particularly high in the far eastern Pilbara and northern Interior where mean minima were over 3 °C above normal. When averaged across WA as a whole, mean minimum temperatures were above average in September 2012, whilst for the Lower Southwest, mean minimum temperatures were near average.
A cold front moving through the southern half of WA on the 27th was followed by a strong southerly stream which brought cold air to southwest WA. Minimum temperatures on the 28th were unusually low as a result and a number of sites recorded sub-zero minima. Karnet in the Lower West recorded a minimum of -0.6 °C, its lowest September temperature in 46 years of recording.
Consistently below average overnight minima for WA from January to August 2012 resulted in the state recording its third coolest January to August period on record; however, the above average September has seen WA's mean minimum for the year to date rise to 8th coolest on record. In contrast, the Lower Southwest has recorded an above average January to September period in terms of mean minimum temperature, with only two months in 2012 (May and July) recording below average mean minima, the only two months to do so since November 2010.
|Extremes in September 2012|
|Hottest day||41.9 °C at Curtin Aero on the 23rd|
|Warmest days on average||38.5 °C at Curtin Aero|
|Coolest days on average||17.6 °C at Rocky Gully|
|Coldest day||9.8 °C at Mount Barker on the 4th|
|Coldest night||-2.5 °C at Eyre on the 30th|
|Coolest nights on average||3.6 °C at York|
|Warmest nights on average||21.1 °C at Argyle Aerodrome|
|Warmest night||27.1 °C at Argyle Aerodrome on the 28th|
|Wettest overall||240.7 mm at Walpole|
|Wettest day||67.2 mm at Bickley on the 4th|
|Highest wind gust||117 km/h at Cape Naturaliste on the 4th|
|Record highest total September rainfall|
for September 2012 (mm)
|Highest total September rainfall for at least 30 years|
for September 2012 (mm)
Most recent September
at least this wet
* note: there are gaps in the historical record at this site, so it is possible a higher value has gone unreported.
|Record lowest September daily maximum temperature|
Lowest daily maximum
in September 2012 (°C)
|Brookton||10.6||on the 4th||= 10.6||on the 22nd in 1968||45||19.1|
|Record highest September mean daily maximum temperature|
Mean daily maximum
for September 2012 (°C)
|Eucla||24.0||= 24.0||in 1981||75||21.3|
|Record lowest September temperature|
in September 2012 (°C)
|Karnet||-0.6||on the 28th||0.0||on the 22nd in 2008||46||7.2|
|Summary statistics for September 2012|
|North Kimberley (district 01)|
|Wyndham Aero||38.2||+0.6||40.8||24th||19.6||-2.3||15.5||16th||0||4.1||v low||0%|
|East Kimberley (district 02)|
|Argyle Aerodrome||37.3||+0.9||40.8||28th||21.1||-1.2||16.8||9th||0||2.6||v low||0%|
|Halls Creek Airport||35.5||+1.5||39.7||23rd||19.7||+0.7||15.2||10th||0||4.6||lowest||0%|
|West Kimberley (district 03)|
|Curtin Aero||38.5||+2.1||41.9||23rd||17.0||-1.5||11.9||1st||0||0.2||v low||0%|
|Fitzroy Crossing Aero||38.5||+1.3||41.9||25th||18.0||-0.7||12.5||11th||0||0.4||v low||0%|
|De Grey (district 04)|
|Marble Bar||36.2||+1.8||39.4||26th||18.0||+1.4||10.5||6th||0||5.6||v low||0%|
|Port Hedland Airport||34.3||+2.0||38.2||15th||15.9||+0.5||11.9||6th||0.6||1.3||average||46%|
|Fortescue (district 05)|
|Barrow Island Airport||27.0||+0.3||31.7||30th||19.9||+0.6||16.9||6th||0.4||0.8||average||50%|
|West Gascoyne (district 06)|
|Emu Creek Station||31.5||+0.9||36.7||30th||14.7||+0.7||11.1||5th||0||2.0||lowest||0%|
|Shark Bay Airport||26.5||+0.8||32.7||30th||13.6||+1.1||8.8||29th||18.2||8.1||v high||225%|
|East Gascoyne (district 07)|
|Murchison (district 07A)|
|Mount Magnet Aero||26.1||+1.8||33.9||16th||11.3||+1.2||4.8||28th||6.2||9.1||average||68%|
|North Coast (district 08)|
|Geraldton Airport Comparison||23.7||+1.7||32.0||16th||10.1||+0.9||3.8||29th||20.6||31.8||average||65%|
|Central Coast (district 09)|
|Badgingarra Research Stn||20.6||0.0||29.2||16th||8.0||+0.5||2.8||28th||73.2||51.4||high||142%|
|Garden Island HSF||19.4||+0.6||27.8||16th||12.4||+0.6||6.7||28th||66.2||60.4||average||110%|
|Medina Research Centre||21.2||+1.0||28.9||9th||10.0||+0.9||2.7||29th||69.0||76.3||average||90%|
|South Coast (district 09A)|
|Albany Airport Comparison||18.2||+0.9||24.0||30th||8.3||+0.3||3.3||24th||134.2||87.2||v high||154%|
|North Central (district 10)|
|South Central (district 10A)|
|Newdegate Research Station||20.8||+2.2||28.6||17th||4.7||-0.1||-2.0||23rd||21.6||33.9||average||64%|
|Eucla (district 11)|
|Red Rocks Point||23.4||37.1||25th||10.0||4.6||9th||11.2|
|South East (district 12)|
|Norseman Aero||23.0||+0.8||31.9||10th||6.6||+0.4||-0.4||13th||7.6||22.4||v low||34%|
|Salmon Gums Res.Stn.||22.2||+1.9||31.9||10th||6.2||+0.5||0.2||13th||25.6||31.7||average||81%|
|Southern Cross Airfield||22.7||+1.3||31.8||10th||6.6||+1.6||-1.3||28th||17.4||21.7||average||80%|
|North East (district 13)|
|Giles Meteorological Office||30.1||+2.7||36.6||26th||14.3||+1.4||5.8||8th||0.4||11.1||low||4%|
|Offshore Islands (district 200)|
|Christmas Island Aero||26.5||+0.3||27.3||12th||22.3||+0.1||21.2||7th||3.6||44.8||v low||8%|
|Cocos Island Airport||28.3||+0.1||28.8||19th||23.9||0.0||20.9||23rd||34.8||93.4||average||37%|
|Varanus Island||27.3||+0.5||29.3||16th||21.1||+0.4||18.8||5th||0||0.4||v low||0%|
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 10 am on Tuesday 2 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,.
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
(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.
*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.