What's Driving the Relentless Rainfall Across NSW ?
It’s been another soggy week in New South Wales, with Sydney drenched almost daily this August. In fact, the city copped 79.9mm of rain in just 24 hours to 9am Thursday – more than the entire monthly average in a single day.
So, what’s going on?
The main culprit is a stubborn high-pressure system sitting over the Tasman Sea. Normally, at this time of year, it would sit further north. But right now, it’s parked unusually far south. Because air circulates anti-clockwise around high-pressure systems, it’s been driving a steady stream of moist air in from the ocean. That moisture then collides with a persistent coastal trough, producing heavy showers and rain day after day.
But there’s another big factor making all of this worse: the ocean itself. Sea surface temperatures off the NSW coast are running much warmer than average. In fact, readings show a big patch of unusually warm water southeast of Sydney – and this warmth has been hanging around all winter, recently intensifying.
These sea surface temperatures are in the top 10% of historical records, which means the atmosphere is being fed more moisture than usual. More moisture equals heavier, more frequent rain.
So, while the high-pressure system sets up the perfect weather pattern for rain, those warmer-than-normal seas are supercharging it.
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