Forecasters warned at the start of spring we’d be in for a wet few months due to a confluence of factors, including record ocean heat off the coast.
Climate scientist at the University of NSW Professor Matthew England said water in the Tasman Sea had been 2 degrees above average. The warm seas feed moisture into the low-pressure system currently spiralling off the coast.
“On top of this, we’ve had onshore easterly winds most days, which is highly unusual for winter, when we normally see prevailing westerlies,” England said.
The latest sea surface temperature map from the Bureau of Meteorology shows a hot blob of ocean water sitting off NSW.Credit: Bureau of Meteorology
“These easterly winds pick up moisture from the ocean, which favours increased coastal rains along NSW. So it’s this combination of record ocean temperatures and prevailing onshore easterlies that has likely led to the record-breaking rains.”
The Indian Ocean Dipole is also tracking towards a negative phase, which can boost rainfall to Australia’s south-east.
Earlier this week, Weatherzone flagged that the Southern Hemisphere’s polar vortex was weakening, which increases the chance of cold fronts and low-pressure systems sweeping over Australia.
The polar vortex is a massive region of cold rotating winds over Antarctica. When the vortex is strong, cold polar winds move southward, pulling cold fronts and lows away from Australia.
“By contrast, a weakened tropospheric polar vortex can allow cold air and powerful winds to spread further away from the polar region,” Weatherzone’s Ben Domensino said.
“This can cause cold fronts and low-pressure systems to push further north and become stronger and more frequent over Australia.”
The heavy rains lashing coastal NSW are expected to ease into Thursday.
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