UPDATE 1-La Nina helps fuel monster Australian cyclone Yasi

Wed Feb 2, 2011 6:27am GMT
 

(Recasts, adds meteorologist comments)

By David Fogarty

SINGAPORE Feb 2 (Reuters) - Record ocean temperatures and an intense La Nina weather pattern have helped spawn one of the most powerful cyclones in Australia but whether there's a direct climate change link is less clear.

Cyclone Yasi, a maximum category 5 storm, was within hours of making landfall in far northern Queensland state and zeroing in on urban centres where more than 400,000 people live.

If it maintained its current intensity when it crossed the coast, it would be the strongest cyclone to hit Queensland since 1899, said Alan Sharp, national manager, tropical cyclone warning services, of the Australian Bureau of Meteorology.

The March 1899 cyclone struck a pearling fleet in Bathurst Bay on Cape York Peninsula, killing more than 300 people in Australia's deadliest storm.

"Yasi is not enormously unusual but it is at the top-end of the scale as far size goes as well as intensity," Sharp told Reuters from Melbourne on Wednesday.

Sharp said the current La Nina was helping drive the record ocean temperatures around Australia that were helping fuel Yasi by providing abundant heat and moisture.

La Nina events historically bring floods and an increase in cyclones during the Australian storm season from November to April.

"We can't say any particular cyclone is caused by climate change. There has been a slight trend towards more intense storms around the world," Sharp said, adding it was hard to figure out what was natural variability or climate-change related.

Scientists say there is a likely climate change link to the current La Nina through higher sea surface temperatures. The world's oceans and atmosphere have steadily warmed over recent decades and that warmth could be providing monsoons and storms with an extra kick.

A major global study in 2010, based on complex computer modelling, found that tropical cyclones will become stronger, with the intensity increasing between 2 and 11 percent by 2100.

And while in some regions, such as the western Pacific and around Australia, the average number of storms might decrease, the number of intense storms in the category 4 and 5 range will increase, along with wind speeds and the amount of rainfall.

Yasi, though, isn't the only monster cyclone to menace Australia.

Cyclone Tracy wiped out much of the city of Darwin on Christmas Day 1974, killing 71 people. The anemometer at Darwin airport recorded a gust of 217 kilometres per hour (135 miles per hour) before the instrument was destroyed, according to the Bureau of Meteorology.

Cyclone Larry ravaged the northern Queensland town of Innisfail in March 2006, becoming Australia's second costliest storm after Tracy.

Weeks later, Cyclone Monica became one of the most intense cyclones ever recorded as it moved just off the coast of the Northern Territory, sparing major townships.

Cyclone George in March 2007 was a large category 5 storm that struck near Port Hedland in northwest Western Australia state, causing three deaths and widespread flooding.

Cyclone Olivia in April 1996 generated a wind gust of 408 km/h on Barrow Island off the Western Australian coast -- a world record.

(Editing by Nick Macfie)

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