"We are going to officially wave off the first attempt," said Ken Ham at mission control

"We're holding some hope for the section option" at the Kennedy Space Center he said, adding that showers and thunderstorms were expected near the facility on Florida's Atlantic coast.

Discovery Commander Eileen Collins took the news in stride after NASA already called off Monday's scheduled touchdown because clouds affected visibility on the runway.

"We understand how unstable weather is in Florida, so we're not surprised at all," Collins told mission control.

NASA said it remained unclear whether conditions would improve in time for the second landing opportunity at KSC.

The Florida space center is the preferred landing site, but NASA could also send Discovery to California, where it could land at the Edwards Air Force Base at 1212 GMT or 1347 GMT.

NASA expected favorable conditions at the California site, but as a last resort Discovery could also land at the White Sands Missile range in New Mexico.

The shuttle could stay an extra day in space if necessary.

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