Weather ‘bomb’ threatens east coast of Australia this week

30 June 2025

Tom Saunders, writing for the Australian Broadcasting Corporation:

When a low-pressure system transforms from non-existence to a formidable storm just a day later, meteorologists label it a “bomb cyclone”, or a system that has experienced “bombogenesis”. The expression “bomb” is due to the explosive speed of development, however its usage is restricted only to systems where the reduction in pressure exceeds a specific rate based on latitude.

A low-pressure weather system forecast to form off the east coast of Australia, near NSW, in coming days, might — when it runs into another system near Queensland that’s moving south — form a so-called “bomb cyclone”. A “bomb” occurs when a low-pressure system experiences a drop in pressure of between fourteen to eighteen hectopascals (hPa) in less than twenty-four hours.

This week’s weather system may see a pressure fall of between twenty-two to twenty-four hPa in the course of a day. That’s a lot it seems, it’s not a good thing, and the result might be the aforementioned “bomb cyclone”. This could lead to heavy rain, gale force winds, and damaging surf.

At this stage it’s not known where the low pressure system will be centred. It might be closer to coast, or someway out in the Tasman Ocean. It’s distance from the east coast will determine its impact. Current modelling suggests areas in the vicinity of Sydney, to the north and the south, will see the heaviest rainfalls, together with regions inland to the northwest of Newcastle.

There is also the prospect of this weather system developing into an East Coast Low. These systems bring intense storms and prolonged rainfalls near to the regions where they are centred.

It’s calm and still as I write this on the NSW Central Coast… the proverbial calm before the storm?