Tropical Storm Shanshan formed over the Western North Pacific Ocean south of Iwo To on Wednesday evening.  At 11:00 p.m. EDT on Wednesday the center of Tropical Storm Shanshan was located at latitude 17.2°N and longitude 141.5°E which put the center about 505 miles (810 km) south of Iwo To.  Shanshan was moving toward the west at 7 m.p.h. (11 km/h).  The maximum sustained wind speed was 45 m.p.h. (75 km/h) and there were wind gusts to 60 m.p.h. (95 km/h).  The minimum surface pressure was 1001 mb.

A low pressure system over the Western North Pacific Ocean south of Iwo To strengthened on Wednesday evening and the Japan Meteorological Agency designated the system as Tropical Storm Shanshan.  The circulation around Tropical Storm Shanshan exhibited more organization on satellite images, but the distribution of thunderstorms was asymmetrical.  Thunderstorms were occurring in bands in the eastern side of Shanshan’s circulation.  Bands in the western side of Tropical Storm Shanshan consisted primarily of showers and lower clouds.  Storms near the center of Shanshan began to generate upper level divergence that pumped mass away from the tropical storm.

The circulation around Tropical Storm Shanshan was small.  Winds to tropical storm force extended out 45 miles (75 km) from the center of Shanshan’s circulation.

Tropical Storm Shanshan will move through an environment favorable for intensification during the next 24 hours.  Shanshan will move over water where the Sea Surface Temperatures are near 29°C.  It will move under the southeastern part of an upper level ridge over Japan.  The ridge will produce northerly winds that will blow toward the top of Shashan’s circulation.  Those winds will cause vertical wind shear, but the wind shear will not be enough to prevent intensification.  Tropical Storm Shanshan will intensify during the next 24 hours.  Shanshan is likely to strengthen to a typhoon within 36 hours/

Tropical Storm Shanshan will move around the western end of a high pressure system over the Western North Pacific Ocean.  The high pressure system will steer Shanshan toward the north-northwest during the next 24 hours.  On its anticipated track, Tropical Storm Shanshan will move closer to Iwo To.  Shanshan could approach Japan in five days.