Tropical Storm Prapiroon moved closer to Okinawa on Saturday. At 11:00 a.m. EDT on Saturday the center of Tropical Storm Prapiroon was located at latitude 22.4°N and longitude 128.3°E which put it about 315 miles (510 km) south of Okinawa. Prapiroon was moving toward the northwest at 8 m.p.h. (13 km/h). The maximum sustained wind speed was 50 m.p.h. (80 km/h) and there were wind gusts to 65 m.p.h. (105 km/h). The minimum surface pressure was 992 mb.
There was a distinct center of circulation in the middle of Tropical Storm Prapiroon, but the distribution of thunderstorms was asymmetrical. The stronger thunderstorms were occurring in bands south and east of the center of circulation. The bands north and west of the center consisted primarily of showers and low clouds. A large upper level ridge over Asia was producing northerly winds which were blowing toward the top of Tropical Storm Prapiroon. Those winds were causing moderate vertical wind shear and they were probably the reason for the asymmetric distribution of thunderstorms. Those winds were also blocking upper level divergence to the north and west of Prapiroon.
Tropical Storm Prapiroon will move through an area marginally favorable for intensification during the next 24 to 36 hours. Prapiroon will move over water where the Sea Surface Temperature is near 29°C. So, there will be enough energy in the upper ocean to support intensification. The upper level ridge will continue to cause some vertical wind shear, but Tropical Storm Prapiroon could move into an area where the upper level winds are a little weaker on Sunday. If the wind shear decreases, then Tropical Storm Prapiroon will intensify. There is still a chance that Prapiroon could strengthen into a typhoon when it passes near Okinawa.
Tropical Storm Prapiroon is moving around the western end of a subtropical ridge over the Pacific Ocean which is steering the tropical storm toward the northwest. Prapiroon is forecast to move more toward the north when it reaches the western end of the ridge in 12 to 24 hours. On its anticipated track the center of Tropical Storm Prapiroon could approach Okinawa in 12 to 18 hours. The center of Prapiroon will likely pass west of Okinawa which would bring the strongest winds and heaviest rain over Okinawa.