SYDNEY, Jan 31 (Reuters) - A rain-bearing La Nina weather pattern, which has begun to end years of serious drought in Australia, was expected to remain until the middle of 2008, the weather bureau said on Thursday.

Australia's parched farm sector welcomed the forecast, although weather officials warned that La Nina also brought the risk of more floods and cyclones.

"There's a higher-than-normal chance of that happening when you're in a La Nina," Brad Murphy, senior climatologist at the National Climate Centre, told Reuters.

"That's always a risk. You never get just the right amount of rainfall everywhere. You either get too much or not enough."

Weather officials have already warned that La Nina, which results from warmer-than-normal sea surface temperatures around Australia's northeast, could make 2008 a 30-year peak cyclone season.

Australia's northeastern coast has already been battered by cyclonic winds and flooding in December and January, creating havoc for holidaymakers and country towns.

This week Cyclone Gene hit Fiji's main island of Viti Levu, 3,500 km (2,200 miles) east of Australia, causing flooding, killing at least six people and shutting down business.

On Thursday, the storm was heading toward Vanuatu and New Caledonia, between Fiji and the Australian coast. Both island nations were on official alert. La Nina was likely to persist at least until late in the southern hemisphere autumn, the Australian Bureau of Meteorology said on Thursday.

"Climate models point to continued moderate La Nina conditions until the middle of 2008," it said.

Parts of eastern Australia have already been hit with severe flooding in December and January. The area is emerging from the worst drought in a century, devastating crops in three of the past six years.

But Australia's key winter grains crops will need rain in April, in the planting season, and in subsequent months, if the country is to produce bumper crops to compensate for losses in recent years.

La Nina weather conditions are the reverse of the El Nino weather pattern, which triggered severe drought across large areas of Australia. El Nino is a warming of ocean temperatures in the western Pacific off South America, triggering a global disruption of weather patterns.

It brings drought to Australia and parts of Southeast Asia and floods to parts of South and North America.

Remnants of the drought still persist, although hopes are high that the present La Nina will eventually bring an official declaration of an end of the drought. (Reporting by Michael Byrnes; Editing by David Fogarty)

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