Forecasters continue to warn of rough seas, high winds and heavy rains for the Marianas after Tropical Depression 12W moved to the west of Guam and Rota and slowly intensified.
National Weather Service officials said the system will continue to move along a northerly course to keep west of the Mariana Islands chain.
But the bulk of rainfall and strong winds remains in the eastern and southern periphery and will persist over the islands for several days.
The system could become a tropical storm by Friday, with sustained winds at 39 mph or higher.
As of Thursday evening, a tropical storm watch was in effect for Rota, Tinian, Saipan, Agrihan, Pagan and Alamagan.
A flash flood is in effect for Guam, Rota, Tinian, and Saipan through late Saturday night. Flash flooding caused by excessive rainfall is possible. Rainfall amounts of 6 to 12 inches are possible through Saturday night.
A small craft advisory is in effect for Guam, Rota, Tinian and Saipan coastal waters through 6 a.m. Sunday. Seas of 8 to 12 feet are expected.
A high surf advisory with a high risk of deadly rip currents is in effect for Guam, Rota, Tinian and Saipan until 6 a.m. Sunday.
A wind advisory is in effect for Guam until 6 a.m. Sunday.