Tropical Storm Mangkhut caused a Typhoon Watch to be issued for the Marianas on Saturday.  A Typhoon Watch was in effect for Guam, Rota, Saipan and Tinian.  At 5:00 p.m. EDT on Saturday the center of Tropical Storm Mangkhut was located at latitude 14.9°N and longitude 156.0°E which put it about 760 miles (1225 km) east of Guam.  Mangkhut was moving toward the west at 24 m.p.h. (39 km/h).  The maximum sustained wind speed was 65 m.p.h. (105 km/h) and there were wind gusts to 80 m.p.h. (130 km/h).  The minimum surface pressure was 983 mb.

The circulation of Tropical Storm Mangkhut became much better organized on Saturday despite its rapid westward movement.  A primary band of thunderstorms wrapped around the southern side of the center of circulation and an eye appeared to be forming.  Winds near the core of Mangkhut were generating upper level divergence which was pumping mass away from the tropical storm.  Several other bands of showers and thunderstorms were revolving around the core of Tropical Storm Mangkhut.  The strongest rainbands were in the western half of the circulation.  Bands in the eastern half of the tropical storm consisted primarily of showers and lower clouds.  An upper level ridge north of Mangkhut was producing easterly winds which were blowing toward the top of the circulation.  Those winds were causing vertical wind shear and they were probably the reason why the strongest rainbands were west of the center of circulation.

Tropical Storm Mangkhut will move through an environment favorable for intensification.  Mangkhut will move over water where the Sea Surface Temperature is near 30°C.  It will move into an area where the upper level winds are weaker and there will be less vertical wind shear.  Tropical Storm Mangkhut will intensify into a typhoon on Sunday and it could intensify rapidly once the inner core and eye are fully formed.

Tropical Storm Mangkhut will move south of a ridge over the Western North Pacific Ocean.  The ridge will steer Mangkhut in a general westerly direction during the next few days.  On its anticipated track Tropical Storm Mangkhut could reach the Marianas in about 36 hours.  It is likely to be a typhoon at that time.  Mangkhut could bring strong winds and locally heavy rain to Guam, Rota, Saipan and Tinian.