Weather officials say a tropical storm has emerged over waters east of the Philippines, warning that it may develop and approach southwestern Japan.

The Japan Meteorological Agency says a tropical depression turned into Tropical Storm Koinu at 3 a.m. on Saturday.

Koinu has a central atmospheric pressure of 1,000 hectopascals. At its center, there are sustained winds of up to 64.8 kilometers per hour and gusts of up to 90 kilometers per hour.

Winds are stronger than 54 kilometers per hour within 330 kilometers southwest of the storm's center and 220 kilometers to its northeast.

The storm is forecast to develop and change its course from westward to northward. It may move further north to approach Okinawa Prefecture, bringing heavy winds.

The agency is calling on people to keep up to date with the latest weather information and warn of possible high waves and intensifying winds in Okinawa.