A weather system approaching the Northern Marianas is expected to develop into a tropical cyclone.
The US National Weather Service says the storm is expected to pass through Federated States of Micronesia, and track near Guam and the Northern Marianas by the end of the week.
It says there is considerable uncertainty about what strength it might develop into.
The Northern Marianas were devastated by Supertyphoon Mangkhut only five months ago, which hit the islands of Tinian and Saipan with winds of more than 200km/h.