Meteorologists have forecasted above average rainfall for much of Australia this summer.
The summer months will follow on from a particularly wet October, during which Williamtown residents saw 186mm of rain fall in just one day on 26 October.
Senior Climatologist for the Australian Bureau of Meteorology (BOM), Felicity Gamble, explained that the wet weather is due to La Niña, a climate driver that is based upon the surface temperature patterns in the tropical Pacific Ocean.
“The model outlook is indicating the La Niña pattern will stay around until the end of summer, back to a neutral phase around mid autumn,” she said.
BOM declared a La Niña, which occurs when surface temperatures in the water are cooler, in turn pushing more cloud cover and rain systems over Australia, in late September.
“La Niña is now underway, so rainfall through to January is likely to be above average for much of the country,” Ms Gamble said.
“With wet soils already in eastern Australia, the risk of flooding with heavy rains is higher than normal.”
BOM Climate Prediction Services Manager, Dr Andrew Watkins, said the last time such an event occurred in Australia was in July 2010, and it went through until early 2012.
“This time, it’s a fair bit dryer coming off the back of the drought we saw in 2019 and, if we look forward in what may happen over the summer in terms of rainfall, in 2010/11 we had a very strong La Niña indeed, one of the four strongest on record,” he said.
“This one might be short and sharp, whereas the one in 2010/11 actually was quite strong for quite a long time as well.”
This year’s forecast sits in stark contrast to last summer’s weather, which, according to BOM, was the “second-warmest summer on record”, and rainfall was “below average for Australia”.
In December 2019, the BOM Signal Station at Nobbys Lighthouse recorded 5.2mm of rain, falling well below the 62.5mm average for the month.
Ms Gamble said it had a drying influence in NSW, which created the ideal conditions for bushfires.
She outlined several climate drivers that influence weather across the Hunter.
“In recent months, we’ve also seen the southern annular mode tend towards more positive values, which is something we see during La Niña events,” she said.
The southern annual mode, or SAM, refers to the north-south shift in the high pressure belt and westerly winds, which has moved south this year, bringing warm, moist air over NSW.
“With weather systems further south than normal, this means more easterly winds over south-east Australia, higher humidity, and increased chances of more rainfall” Ms Gamble added.
From now until January, temperatures are likely to be cooler than average in coastal NSW, according to BOM’s forecasts.
However, forecasts also predict that nights are “very likely” to be warmer than average, due to increased cloud cover, resulting in fewer clear nights.