Tropical Storm Hinnamnor formed east of Iwo To on Sunday morning. At 5:00 a.m. EDT on Sunday the center of Tropical Storm Hinnamnor was located at latitude 26.2°N and longitude 148.8°E which put it about 510 miles (825 km) east-northeast of Iwo To. Hinnamnor was moving toward the north-northwest at 14 m.p.h. (22 km/h). The maximum sustained wind speed was 40 m.p.h. (64 km/h) and there were wind gusts to 50 m.p.h. (80 km/h). The minimum surface pressure was 997 mb.

The circulation around a low pressure system east of Iwo To strengthened on Sunday morning and the Japan Meteorological Agency designated the system as Tropical Storm Hinnamnor. The circulation around Hinnamnor was still organizing. The inner end of a rainband wrapped around the western and southern sides of the center of circulation. Other bands of showers and thunderstorms were revolving around the center of Tropical Storm Hinnamnor. Storms near the center of circulation generated upper level divergence that pumped mass away from the tropical storm. Winds to tropical storm force extended out 140 miles (225 km) on the eastern side of Hinnamnor’s circulation. Winds to tropical storm force extended out 75 miles (120 km) on the western side of the circulation.

Tropical Storm Hinnamnor will move through an area favorable for intensification during the next 24 hours. Hinnamnor will move over water where the Sea Surface Temperatures are 30˚C. It will move through region between an upper level trough over Japan, a small upper level low northwest of the Marianas, and a larger upper level low east of the Marianas. The upper level winds are weak in the region between the upper level trough, and the two upper level lows. Tropical Storm Hinnamnor will be in a region where there is little vertical wind shear during the next 24 hours and it is likely to intensify.

Tropical Storm Hinnamnor will move around the southwestern part of a high pressure system that extends over Japan. The high pressure system will steer Hinnamnor toward the west during the several days. On its anticipated track the center of Tropical Storm Hinnamnor could be north of Iwo To in 36 hours.