Tropical Depression 28W formed over the Mariana Islands on Thursday. At 5:00 p.m. EDT on Thursday the center of Tropical Depression 28W was located at latitude 14.1°N and longitude 144.8°E which put it about 15 miles (25 km) east-northeast of Guam. It was moving toward the northwest at 10 m.p.h. (16 km/h). The maximum sustained wind speed was 35 m.p.h. (55 km/h) and there were wind gusts to 45 m.p.h. (75 km/h). The minimum surface pressure was 1002 mb. Tropical Storm Watches were issued for Rota, Saipan and Tinian.
Tropical Depression 28W was still organizing on Thursday. A distinct center of circulation formed in an area of thunderstorms near the Marianas. Bands of showers and thunderstorms developed around the circulation. The strongest rainbands were forming in the eastern half of the circulation. Bands of showers and thunderstorms were also forming in the western half of the circulation but there were fewer strong thunderstorms in that half of the tropical depression. Storm closer to the center of circulation were starting to generate upper level divergence which was pumping mass away from the depression.
Tropical Depression 28W will move through an environment favorable for intensification. It will move over water where the Sea Surface Temperature is near 30°C. The tropical depression will move through an area where the upper level winds are weak and there will be little vertical wind shear. Tropical Depression 28W will intensify during the next few days. It is likely to strengthen into a tropical storm on Friday and it could intensify into a typhoon during the weekend.
Tropical Depression 28W will move around the southern side of a subtropical ridge over the Western North Pacific Ocean during the next several days. The ridge will steer the depression in a general west-northwesterly direction. On its anticipated track the depression could be southeast of Okinawa in four or five days and it is likely to be a typhoon at that time.