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Perth notches hottest September on record, driest in 42 years as weather warms up

By Irena Ceranic, Tuesday October 1, 2019 - 10:18 EST
ABC image
The warmth felt in Perth during September is likely to continue for the rest of spring. - ABC

Perth has just posted its hottest September on record and the driest in 42 years, setting the scene for a sizzling spring and summer to come.

The city's average maximum for the month was 22.9 degrees Celsius, which is 2.6C higher than the September average of 20.3C.

"This was helped along by a good nine days above 25 degrees during September including two days over 30 degrees," Bureau of Meteorology forecaster Angus Moore said.

In fact, it was the warmest September on record for Western Australia as a whole, with the mean maximum 2.18C above average.

The 31.4 millimetres of rain recorded in Perth's official Mount Lawley gauge fell well short of its 84.8mm September average.

Many parts of the south-west were exceptionally parched too.

"That makes it the driest September we've seen since 1977," Mr Moore said.

Mr Moore said ridges of high pressure which dominated the weather pattern for much of the month kept rain-bearing cold fronts away.

"As a month in the transition season between winter and summer, we still expect to see pretty vigorous cold fronts coming through during September," Mr Moore said.

"This time around we just haven't seen those fronts moving through the south-west corner of the state as often as we might expect."

Spring is generally a season of wild fluctuations, but even so, September was a month of extremes in Australia.

Bushfires raged in parts of Queensland and New South Wales, snow fell at very low elevations and strong winds whipped up dust storms.

The was also widespread frost over inland areas and heavy rain on the east coast, with Sydney notching up almost a month's worth of rainfall in one day.

A hot summer ahead

The warmth felt in Perth during September is likely to continue for the rest of the season and trickle into summer.

The BOM Climate Outlook suggests maximum temperatures are highly likely to be above average over much of Australia during the remainder of the year, increasing the chance of early heat waves.

With less cloud about, nights are likely to be cooler than average across parts of south-eastern and northern Australia between October and December, with warmer nights likely elsewhere.

Rainfall is expected to be below average across most of Australia for the rest of the year and early 2020.

The exception is Western Australia's north-west, where there are slightly increased chances of above average rainfall between October and December.

A positive Indian Ocean Dipole (IOD) will be the main influence on Australia's weather over the coming months.

A positive phase of the IOD occurs when sea surface temperatures to the north-west of Australia are cooler than normal, reducing the amount of moisture to be dragged across Australia by rain-bearing clouds associated with cold fronts and low pressure systems.

A prolonged negative Southern Annular Mode (SAM) has also been forecast, which brings more bad news for those hoping for rain.

In a negative SAM phase, westerly winds shift further north than usual, and in summer this lessens the moist onshore flow from the east, resulting in decreased rainfall over eastern Australia.


© ABC 2019

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