A tropical cyclone warning has been issued for Aitutaki, in the Cook Islands. Wind gusts up to 50km per hour are predicted.
Cylone Sarah follows Cyclone Pat which battered the island two weeks ago.
A gale warning has also been issued for Palmerston and a strong wind warning is in place for the rest of the southern Cook Islands.
The cyclone may prevent a relief mission by the Royal New Zealand Air Force, which is trying to deliver supplies to the remote atoll of Penryn which has been hit by a number of storms.
An RNZAF Hercules arrived in the Cook Islands on Friday and a decision will be made on Saturday on whether it will still be able to fly to the atoll. About 200 people live there.
The Hercules is carrying a generator, chainsaws, tarpaulins, and building and medical supplies.
Squadron Leader Kavae Tamariki says the mission includes collecting air force personnel who have been working on the cleanup of Aitutaki.