SYDNEY — A strong tropical cyclone roared toward Australia’s flood-ravaged northeast today, prompting evacuations and warnings from officials that the storm could be the worst the already-swamped region has ever seen.

Cyclone Yasi strengthened to a Category 3 today with winds up to 115 mph. It was expected to hit the Queensland state coast on Wednesday or Thursday as a fierce Category 4 storm with wind gusts up to 162 mph. The storm could dump up to three feet of rain on some communities already saturated from months of flooding, Queensland Premier Anna Bligh said.

But Yasi is expected to strike somewhere along the state’s north coast, largely avoiding areas to the south that have suffered the worst of the recent flooding.