Authorities had imposed a nationwide curfew as Zena bore down on the main island Viti Levu overnight yesterday, fearing a repeat of super cyclone Winston, which killed 44 people in February.
But meteorologists said Zena weakened, rather than intensifying, and tracked further south than expected, staying out to sea and leaving the island relatively unscathed.
"After a blissfully uneventful night across Fiji we can give thanks," Suva's Nadraki weather forecasting service said.
"All who planned for the worst and hoped for the best were rewarded for their efforts by having everything turn out okay."
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"Viti Levu has been spared a second major disaster in as many months," it said.
"The weather has now dramatically improved in most areas and flood waters are starting to subside."
Roads reopened and international flights resumed, with a police-enforced curfew lifted early today.
But OCHA said the thousands of people still in temporary accommodation after Winston -- the most powerful storm in Fiji's history -- had a "miserable night" in heavy rains.
Forecasters said Zena had been downgraded to a category two system and was heading east towards neighbouring Tonga, where authorities warned residents to expect thunderstorms, high winds and heavy swells.