Via the Sydney Morning Herald: Cyclone Ita due to hit tonight and likely to lift roofs, uproot trees. click through for the full report, photos and maps, and a 2-minute video. Excerpt:
Trees will start to topple, roofs will be sucked up and solar panels might start flying like Frisbees as severe tropical Cyclone Ita makes landfall in far north Queensland this evening, wind experts say.
The Bureau of Meteorology predicts wind speeds for the Category 5 storm to approach 300km/h as it approaches the coast near Cape Flattery, north of Cooktown.
“If we do get 300km/h that is slightly stronger than Cyclone Yasi,” which ripped through north Queensland near Innisfail in 2011, said Grahame Reader, the severe weather manager at the bureau. “Physically, (Ita's) a relatively small storm but it's intense.”
Wind speed measurements are largely drawn from satellite imagery of clouds and radars, with only a few land-based devices, known as anemometers, on hand.
James Cook University, though, is testing mobile anemometers mounted on anchored trailers for the first time to get more accurate readings, said John Ginger, research director of the university's Cyclone Testing Station. Estimates now are largely gained after the event when bent-over street signs are examined closely for clues.
Dr Ginger said branches and other debris typically start to break off when wind speeds reach about 100km/h, and shallow-rooted trees begin to topple when sustained gusts reach about 160km/h.
The force of wind rises at four times the speed, so that by 200km/h houses typically start to lose guttering and other material. Houses built to pre-1980s standards also begin to be at risk, while those built since should be able to withstand speeds of 250km/h or more.
John Holmes, director of JDH Consulting and chair of the body setting wind loading standards in Australia, said cyclones lose wind speed quickly once they make landfall.
Yasi, for instance, was more like 180km/h in strength when it crossed the coastline – still strong enough to cause significant damage.
“There were some solar panels and things that took off like Frisbees,” Dr Holmes said. “It's not a good place to be wandering around outside in.”
More newly built houses have more steel connections, particularly to prevent roofs blowing off. Airborne debris, for instance, can smash windows or garage doors that weaken the building's protection.