Typhoon Jangmi is expected to develop into a large and powerful storm when it reaches the south of Okinawa Prefecture by 9 a.m. on Monday, according to the Japan Weather Association.According to the Japan Meteorological Agency, as of 9 a.m. on Saturday, Jangmi was moving northwest over the waters east of the Philippines at a speed of 15 kph. The central pressure is 992 hectopascals, and the maximum wind speed near the centre is 23 meters per second.