Flood-ravaged Queensland Braces for Tropical Cyclone Yasi

February 1, 2011

Just as TC Anthony dissipated over Queensland the flood ravaged State received a warning that another tropical cyclone is heading its way. According to catastrophe modeling firm AIR Worldwide, Cyclone Yasi was “about 1630 kilometers [1018 miles] east northeast of Mackay and moving west at 30 km [18.75 mph] as of the Australia’s Bureau of Meteorology 11:00 EST advisory.

The storm is a strong one with gust wind speeds of around 205 kph (128 mph). AIR said a “cyclone watch is in effect for 900 kilometers [562.5 miles] of Queensland’s coast, stretching from the island communities from Cooktown to Yeppoon and inland between Georgetown and Moranbah.

AIR Worldwide scientist Jason Butke explained: “Yasi, which only became a cyclone on Saturday, strengthened rapidly since its formation. On Sunday, the storm passed north of Vanuatu, bringing strong winds and high waves. Presently, Yasi—a moderately-sized storm with cyclone-force winds extending outward 55 kilometers [35 miles]—remains overseas with warmer-than-average surface temperature and is experiencing low-to-moderate wind shear conditions. While in this favorable environment, the storm should continue to gradually strengthen, possibly nearing Category 4 strength by Wednesday afternoon when it is forecast to make landfall in northern Queensland.”

As a result Queensland is in serious danger of another round of extreme flooding this week. In addition to the storm’s damaging winds and storm surge, Yasi will bring torrential rains to already saturated soil. “Although cyclone Yasi is currently expected to impact areas to the north of Brisbane and areas heavily flooded earlier in the month, a more southerly turn in storm track could dramatically change the flooding potential,” Butke added.

AIR forecast precipitation estimates on the order of “200-400 mm [7.874 to 15.748 inches] with amounts as high as half a meter [app. 40 inches] are possible. A moderate forward speed of 30 km/h [18.75 mph] should limit the most extreme precipitation scenarios. The latest TRMM (Tropical Rainfall Measuring Mission) meteorological data indicates rainfall rates near 20 mm/hr [app ¾ inch] in the eye wall and 200-400 mm in the wake of the storm.”

Butke warned that “storm surge also poses a threat, particularly if Yasi strikes at high tide. In Townsville, the difference between low and high tide is about 3 meters [app.10 feet] while in Cairns, it is as high as 2.5 meters [over 8 feet]. The final surge heights will depend on the state of the tide.”

At this point the storm’s track, and the areas it could impact, cannot be precisely determined. But the cities of Innisfail and Mackay seem to be in its likely path. AIR also that the coastal cities of Cairns and Townsville are both forecast to experience destructive or very destructive winds from Yasi. “In comparison to Cairns and Townsville, the area that lies in-between these two cities is not as populated, meaning that the wind damage potential could be moderate if Yasi makes landfall between the two cities,” Butke stated. “However, if the scenario takes Yasi toward either regional city, the wind damage could be significant.”

According to AIR, at Category 3 or 4 wind speeds, damage is expected to be significant. Structural damage to houses and buildings may occur, particularly to rooftops, while windows and cladding on engineered structures could be damaged by impact from debris. Many trees will likely be uprooted and snapped, blocking roadways or damaging homes and automobiles. However, strong building codes have been in place since the 1960s in north Queensland, and they will help mitigate the effects of high winds and associated debris.

“An especially strong, near record-breaking, La Niña event is affecting Australia, contributing to the precipitation-induced flooding in Queensland and increasing the frequency and likely potential intensity of cyclones,” added Butke. As reported in the latest BOM climate statement and flood summary, the past four months (September – December) have been the rainiest such period in Queensland’s history.
According to AIR, “comparisons to Cyclone Larry, a powerful 2006 storm that wrought A$1 billion in damage, are inevitable. The track of Larry and the forecasted track of Yasi are quite similar; however, Yasi will likely be a larger, but somewhat less intense storm.”

Source: AIR Worldwide

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