HAGATNA, Guam » Guam and the Northern Mariana Islands are preparing for a major storm that may become a typhoon.

Tropical Storm Bavi was expected to make its closest approach between Sunday night and Monday morning, the Guam newspaper Pacific Daily News reported.

The storm was located 830 miles east of Guam as of Saturday morning local time, the National Weather Service said. It was moving west toward the Mariana Islands with maximum sustained winds of 50 mph.

The agency has issued a typhoon watch for Guam, Rota, Tinian and Saipan. This means winds of 73 mph or greater are possible within the next 48 hours.

The storm has doubled its speed since Thursday and is expected to intensify in the next few days.

Bruce Williams, Guam’s Department of Education safety coordinator, said officials would decide by Sunday evening whether schools will be closed on Monday.

Guam Waterworks Authority advised residents to do their laundry and stock up on water as early as possible this weekend in the event the storm disrupts the island’s water service.