A center of circulation consolidated near a cluster of thunderstorms south of Japan on Saturday and the system was designated as Tropical Storm Chanthu.  At 11:00 p.m. EDT on Saturday the center of Tropical Storm Chanthu was located at latitude 21.2°N and longitude 143.1°E which put it about 295 miles (475 km) south-southeast of Iwo To.  Chanthu was moving toward the northeast at 14 m.p.h. (23 km/h).  The maximum sustained wind speed was 40 m.p.h. (65 km/h) and there were wind gusts to 50 m.p.h. (80 km/h).  The minimum surface pressure was 998 mb.

Although a distinct center of circulation exists in the lower levels of Tropical Storm Chanthu, the storm is not well organized.  Southwesterly winds in the upper levels are causing vertical wind shear which is tilting the upper portion of the circulation toward the northeast.  Most of the thunderstorms associated with Tropical Storm Chanthu are occurring in the northeastern quadrant of the circulation.  Several broken rainbands extend into the southern portion of the circulation, but there are few thunderstorms in the western half of Chanthu.

Tropical Storm Chanthu is moving through an environment that is marginally favorable for intensification.  Chanthu is moving over water where the Sea Surface Temperature is near 30°C.  However, an upper level trough west of Chanthu is causing the southwesterly winds which are blowing across the top of the tropical storm.  Moderate vertical wind shear will inhibit intensification in the short term.  As Tropical Storm Chanthu moves farther north, it could move into a region where the upper level winds are not as strong.  If the vertical wind shear decreases, then Chanthu could intensify.

Winds from the upper level trough are steering Tropical Storm Chanthu toward the northeast.  As the tropical storm moves farther north, a subtropical ridge located east of Chanthu will steer it more toward the north.  On its anticipated track, the center of Tropical Storm Chanthu is expected to pass east of Iwo To in about 24 hours.  Tropical Storm Chanthu could be approaching the coast of Japan near Tokyo in about three or four days.