Monday, 3 September 2012 - Monthly Climate Summary for Western Australia - Product code IDCKGC11R0

Western Australia in August 2012: A very warm and dry month

• Rainfall: 9th driest on record for WA; below average for southwest WA
• Maximum temperature: 2nd highest for WA; above average for southwest WA
• Minimum temperature: near average

Extremes Maps Records Summaries Important notes the top

Rainfall

Rainfall during August 2012 was below to very much below average throughout much of WA (see the maps below). Rainfall was particularly low in the southeast of the state where several sites in the Eucla recorded less than 3 mm for the month and Eyre observed its lowest August rainfall in 83 years of record (see the records tables below). No rainfall was reported in the Kimberley during the month, as is typical in August; however, coastal parts of the Kimberley did report a high number of fog and dew events and so above average "rainfall" in these areas was the result of condensation rather than precipitation. For WA as a whole, August 2012 ranked 9th driest on record, whilst for the Lower Southwest (southwest of a line from Jurien Bay to Bremer Bay) and for the Southwest Land Division (SWLD) rainfall was also below average.

Heavy rainfall in the Central West due to a cold front and developing cloudband on the last day of July 2012 resulted in a few stations observing their highest August daily rainfall on record, with totals in the 24 hours to 9am on the 1st in the 45 mm to 50 mm range. A generally westerly flow and a series of cold fronts over southern WA during the first week of August 2012 brought consistent rainfall to the region, although daily totals after the 1st were mostly only light to moderate. The most significant rainfall amounts during this period were due to a cold front moving across southern WA on the 6th and 7th, with moderate rainfall observed in parts of the Lower West, Southwest, and Great Southern, followed by isolated thunderstorms and small hail in southern parts of the Southwest and South Coastal districts in the cold airmass behind the front on the 8th. Karnet observed the highest fall during the event of 44.0 mm in the 24 hours to 9am on the 7th. A ridge developed over the south of the state in the wake of the front on the 8th, with a strong high moving into the Bight from the 9th to the 11th maintaining generally clear conditions across WA. A cloudband with areas of rain extended across the SWLD on the 12th, and into the southern Gascoyne and Goldfields during the evening, with moderate to heavy falls observed in the Lower West and Southwest districts. The highest daily total in the 24 hours to 9am on the 13th was 53.0 mm at Mundaring, which was the highest daily total at the site for over six months, since 68.8 mm was observed on 20 January 2012. The cold front and cloudband moved eastward through southern WA on the 13th, clearing to the east of the state in the evening with generally light showers observed with the front. A ridge developed across southern WA in the wake of the front on the 13th and remained the main synoptic feature through to the 18th, with mostly clear conditions over WA apart from some showers along the south coast. A surface trough moved eastward through central WA on the 19th as a cold front moved through the Bight with cloud extending over much of southern WA from the west, and isolated showers observed in far southern parts of the SWLD. On the 20th, the cold front moved eastward across the Eucla coast as a low approached the southwest corner of the state late in the evening, with isolated light showers over central and southern parts of the SWLD, as well as the adjacent southern Goldfields, extending into coastal parts of the Central West in the evening. A trough and cold front moved through southern WA on the 21st and 22nd, with light to moderate rainfall observed throughout the SWLD and adjacent parts of neighbouring districts, whilst a southwesterly flow behind the front brought generally light falls to southern parts of the SWLD and Eucla in the 24 hours to 9am on the 23rd. A ridge developed over the south of the state on the 24th with generally clear conditions persisting until the 26th, apart from isolated showers along the south coast and showers and thunderstorms in the northern Goldfields early on the 25th due to a mid-level disturbance. A westerly flow over the southwest of the state from the 27th through to the 29th with embedded weak cold fronts brought isolated showers to mainly southern and western parts of the SWLD, before showers contracted to southern coastal parts on the 30th as a ridge developed over the south of the state. A cold front moved into the SWLD on the last day of the month bringing light showers to the southwest corner, slowly extending throughout the SWLD during the day.

The Lower Southwest has recorded its 5th driest January to August 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. The SWLD has similarly recorded its 6th driest January to August period in 2012 as a result of recording its 6th driest autumn and 9th driest winter, including the 2nd driest July on record.

Maximum temperature

Maximum temperatures during August were above to very much above average throughout WA, with areas of highest on record in large parts of the Pilbara and west Kimberley as a number of sites registered their warmest August on record. Southern parts of the Pilbara, and the northern and central inland Gascoyne saw mean maximum temperatures up to 5 °C warmer than normal. When averaged across the state as a whole the mean maximum temperature during August 2012 ranked as 2nd highest on record for WA, continuing a run since April of five 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) as August 2012 continued the very warm year to date in the region. All months apart from February have seen above average mean maxima, with the mean maximum for January to August 2012 being 0.9 °C above normal and ranking 3rd warmest 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 winter. This run of "warm" temperatures has persisted for almost three years as the Lower West has only recorded two months below the average, in terms of mean maximum temperature, since October 2009.

Relatively warm days were observed in central and southeastern parts of WA on the 6th and 7th in warm northerly winds ahead of a cold front with temperatures in the mid-twenties on the 6th reaching the low thirties on the 7th. A trough near the west coast and a high in the Bight directed warm northeast winds over western parts of the state on the 10th, with temperatures up to 10 °C above normal in inland areas of the Gascoyne and northern SWLD. The warm weather continued over much of western WA on the 11th, away from coastal parts of the Gascoyne and west coast parts of the SWLD with temperatures in the high twenties to low thirties in eastern parts of the SWLD, southwest Gascoyne, and adjacent Goldfields. The focus of the warm weather shifted to the southeast Gascoyne, Goldfields and Southeast Coastal, and adjacent Interior and Eucla on the 12th as a cold front approached the west coast, with temperatures up to 10 °C warmer than normal. A high moving south of WA resulted in warm to hot conditions through northwest and central parts of WA from the 16th through to the 21st, with hot days observed in the west Pilbara and Gascoyne on the 18th, contracting to the Gascoyne and northern Goldfields on the 19th and 20th, and to the Interior and Pilbara on the 21st. Onslow Airport observed its warmest August temperature in 48 years of record on the 18th, with a maximum of 35.2 °C, while Roebourne Aerodrome equalled its highest August temperature in 11 years of record on both the 20th and 21st with maxima of 35.9 °C. A high over southern Australia brought warm to hot conditions to much of WA from the 24th to 26th and the hot conditions slowly contracted to central and northern WA on the 27th and 28th. Fitzroy Crossing recorded the highest temperature in the state for August 2012 with 38.5 °C on the 27th, only slightly below its 42 year August record of 39.0 °C, whilst Telfer Aerodrome recorded a maximum temperatue of 36.0 °C on the 28th, its equal highest August temperature in 39 years of record. Warm conditions returned to western parts of WA away from the west coast with temperatures up to 10 °C warmer than normal in northerly winds ahead of a cold front.

Minimum temperature

Below to very much below mean minimum temperatures were observed across the Kimberley, adjacent Interior, and coastal east Pilbara during August 2012, with areas of lowest on record in the north and west Kimberley where temperatures were up to 5 °C cooler than normal. Wyndham recorded a mean minimum of 15.1 °C, its lowest August mean minimum in 44 years of record. Areas of below average mean minima were also observed in the Southwest and Great Southern, as well as in the eastern Interior and eastern Eucla. In contrast, most of central, western, and southern WA saw above to very much above average overnight temperatures with areas of up to 2 °C warmer than normal in the west Pilbara, Gascoyne, Goldfields, and Interior.

Mean minimum temperatures were near average when averaged across both WA as a whole, and across the Lower Southwest.

Generally clear skies and light winds resulted in a cool morning in the north of the state on the 1st, contrasting with warm overnight temperatures in the Gascoyne, Goldfields, eastern SWLD and western Eucla as cloud extended across the state. Whilst cloudy conditions remained over central parts of WA on the 2nd resulting in warm minima, the cool conditions continued in the north of the state, with Curtin Aerodrome observing a minimum of 6.9 °C and Kununurra Aerodrome observing a minimum of 7.8 °C, their lowest August minimum temperatures in 20 and 26 years of record respectively. Another cold morning was observed in the north of the state on 3rd as Kununurra Aerodrome again broke its lowest minimum temperature record for August with a minimum of 7.3 °C, 0.7 °C cooler than the previous record of 8.0 °C set on 3 August 1990. Further cool mornings were observed in the Kimberley on the 4th and 5th, and 7th to 9th. Curtin Aerodrome equalled its previous lowest August temperature of 8.4 °C on the 8th, though this was above the new low of 6.9 °C observed on the 2nd of the month. A cold morning was experienced in southern parts of WA on the 9th and 10th as a ridge developed in the wake of a cold front and a number of locations registered sub-zero minima. Cloudy conditions and northerly winds resulted in a warm morning in the Goldfields and southeast SWLD on the 12th, while clear skies and light winds resulted in cool mornings returning to the Kimberley from the 12th to 15th. Kununurra Aerodrome equalled its previous August record on the 12th, then broke it for the third time in the month with a minimum of 7.3 °C on the 14th, thus breaking or equalling its previous record on four occasions during August 2012. Curtin Aerodrome also achieved the feat on five occasions during the month. Very cold mornings were observed in southern WA on the 14th and 15th as a ridge extended across the region, with temperatures well below freezing in the southern Goldfields and Eucla on the 14th. Cloudy conditions and a generally northerly flow resulted in a warm morning in parts of western WA on the 21st, with temperatures in the mid-teens in the northern SWLD and adjacent Gascoyne.

WA has observed its equal 3rd coolest January to August period on record due to mean monthly minima being consistently below the average in 2012, and particularly as a result of a very cold May (5th coldest) and the coldest July since comparable records commenced in 1950. In contrast, the Lower Southwest has recorded an above average January to August period in terms of mean minimum temperature.

Extremes Maps Records Summaries Important notes the top

Maps
	Observed	Anomaly	Decile rank
Total rainfall
Mean daily maximum temperatures
Mean daily minimum temperatures

Extremes Maps Records Summaries Important notes the top

Extremes Maps Records Summaries Important notes the top

Extremes Maps Records Summaries Important notes the top