'Rain bomb' is actually a river: expert

Politicians have enthusiastically embraced the term ‘rain bomb’ to describe a weather system that has flooded parts of NSW and Queensland. But there’s no such thing. Meteorologists say it’s actually an atmospheric river that’s less like a bomb and more like a conveyor belt, delivering a relentless stream of moisture-laden air. The west coasts of the United States and Canada are frequently walloped by one dubbed the Pineapple Express, which transports moisture over 4000km from around Hawaii. “We don’t have any names for them here in Australia,” says Ben Domensino, a meteorologist from commercial weather company, Weatherzone. “But it’s common for these atmospheric rivers to affect eastern Australia. “All an atmospheric river is, is a very long area of winds, blowing in the same direction over the ocean. It drags moisture thousands of kilometres. When those winds meet a landmass, the air rises and the moisture is converted into rainfall.” In the case of the system swamping Australia’s east coast, the area of the ocean the winds are blowing over has extended up towards New Caledonia. “These winds have been blowing across that stretch of ocean, and pushing moisture that evaporated from the ocean, towards Australia,” Mr Domensino says. He jokes that it’s technically New Zealand’s fault the system hovered over southeast Queensland for so long before gradually moving south. “The reason it sat there so long is because there’s been what’s called a blocking high pressure system over NZ. “When you get a very strong area of high atmospheric pressure sitting over NZ, it holds weather systems over eastern Australia, and doesn’t let them move away. “Unfortunately they are to thank for this.” The system that has caused devastating flooding in Queensland and northern NSW is delivering constant rain from the NSW mid-north coast to the south coast, including Sydney, Wollongong and Newcastle. But there’s a new threat - a low pressure system that has formed and is starting to interact with the atmospheric river. “So you’ve got that low pressure system strengthening. It’s just sitting at the edge of that atmospheric river,” Mr Domensino says. “As that low pressure system moves in towards the coast ... it will just cause an area of even heavier rain, where there’s already been lots of rain.”