Tropical Storm Chan-hom formed southwest of Iwo To on Sunday night.  At 11:00 p.m. EDT on Sunday the center of Tropical Storm Chan-hom was located at latitude 22.8°N and longitude 139.0°E which put it about 215 miles (345 km) southwest of Iwo To.  Chan-hom was moving toward the west-northwest at 3 m.p.h. (5 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.

More thunderstorms developed near the center of a low pressure system southwest of Iwo To on Sunday night and the Japan Meteorological Agency designated the system as Tropical Storm Chan-hom.  The circulation around Tropical Storm Chan-hom was still organizing.  Thunderstorms were forming near the center of circulation, but the distribution of storms was asymmetrical.  The strongest thunderstorms were developing in bands in the southern half of the tropical storm.  Bands in the northern half of Chan-hom consisted mainly of showers and lower clouds.  Storms near the center of circulation generated upper level divergence which pumped mass away to the west of the tropical storm.  Winds to tropical storm force extended out 100 miles (165 km) in the southeastern quadrant of Tropical Storm Chan-hom.  Winds in the other parts of Chan-hom were blowing at less than tropical storm force.

Tropical Storm Chan-hom will move through an environment favorable for intensification during the next several days.  Chan-hom will move over water where the Sea Surface Temperature is near 28°C.  It will move around the southern side of an upper level ridge.  The ridge will produce easterly winds which will blow toward the top of Tropical Storm Chan-hom.  Those winds will cause some vertical wind shear.  The shear will inhibit intensification but it will not be strong enough to prevent Chan-hom from intensifying.   Tropical Storm Chan-hom could strengthen into a typhoon within 72 hours.

Tropical Storm Chan-hom will move around the western end of a subtropical high pressure system over the Western North Pacific Ocean.  The high will steer Chan-hom toward the northwest during the next two to three days.  On its anticipated track Tropical Storm Chan-hom could approach the northern Ryukyu Islands and southwestern Japan by the end of the week.