Temperature
and rainfall records tumble as unseasonal weather grips WA
Cold
in Far North Queensland| Records, records everywhere... Overnight minimum temperatures (below, top) were up to 11° above normal across the southwestern third of WA, giving Perth Airport and possibly other locations their warmest July night on record, while in Far North Queensland, Cooktown recorded its coldest July night. Maximum temperature variations (middle) were just as great, producing another crop of records. Widespread rain in the same area broke yet more records and eased the drought. The map (bottom) shows total rain for the week ended 31 July, though the rain in SW WA all fell over 4 days to 31 July. BoM  |
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The record warmth allowed unseasonably high moisture levels to develop. The warm tropical air has been drawn down from the northwest ahead of a slow-moving trough, bringing dew points of around 15° which is unusually high for winter. Though cloud in the humid airmass was patchy, it developed explosively during yesterday evening in response to strong upmotion in the lower and middle atmosphere ahead of a troughline. Perth Airport recorded 63.2mm in the four hours to 9 last night. The airport's 24 hour total to 9 this morning of 107.6mm is its heaviest July one-day fall in nearly 60 years of record. Bickley, on the Darling Escarpment 20km ESE of the airport, recorded 99mm in the nine hours to midnight this morning for a 24 hour total of 137, while nearby Mundaring topped the list with 158mm. Widespread power cuts and some flooding were reported around Perth.
While the humidity streamed southeastwards, the stream as a whole was pushed to the east by the advancing trough, giving heavy rain from the Central West to the Great Southern during the morning and east as far as Esperance later in the day. Details of heavy 24 hour falls, short duration falls, and records are given in the National Weather Extremes below, and for yesterday.
In addition to breaking its July rainfall record, Perth Airport also registered its warmest July night on record, the minimum of 16 (rounded) being nearly a degree warmer than the previous record in nearly 60 years of measurement at the site. With overnight minima between 10 and 13 above normal from the Murchison to the Goldfields, it is likely that other records have also fallen.
To the east of the rainband, maximum temperatures were also 10 to 13 above normal, with Kalgoorlie-Boulder Airport recording its hottest July day in 60 years of measurement when the mercury rose to 28.7. Yeelirrie station, 400km north of Kalgoorlie, which broke its 27 year July maximum record yesterday, surpassed it today with a reading of 28.6.
The rains came the day after Prime Minister John Howard announced interim drought relief measures for wheat belt and Great Southern farmers. The area shown in green in the rainfall map at left corresponds closely with the area that has received either record low rainfall during the past year, or falls in the lowest 10% of record. In some areas, the drought is the worst in nearly a century. Lake Grace, 275km SE of Perth, had recorded only 94.4mm in the 11 months from 1 September last year to yesterday morning, but received 31mm to 9 this morning, and a further 9mm during the day.
Southerly winds generated by the Tasman Sea low that battered the NSW coast on the 28th arrived in Far North Queensland yesterday, bringing cool, dry and cloudless conditions. Unusually low minimum temperatures resulted overnight, with Cairns reporting 8.1°, 9 below, and Cooktown a record-breaking 8.0°, 10.2 below.