Tropical Depression 04W formed east of the Northern Marianas very late on Friday. At 11:00 p.m. EDT on Friday the center of Tropical Depression 04W was located at latitude 18.8°N and longitude 148.5°E which put it about 185 miles (300 km) east of Agrihan. It was moving toward the northwest at 11 m.p.h. (17 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 1003 mb.
An area of showers and thunderstorms persisted for much of the past week east of the Northern Marianas. Several smaller centers of circulation formed within the area of showers and storms, but those centers ran into strong upper level winds and weakened because strong vertical wind shear and they dissipated. Another center formed on Friday, but the upper level winds were a little weaker and the center persisted. An upper level trough south of Japan was still producing southwesterly winds which were blowing toward the top of the circulation. Those winds were producing moderate vertical wind shear, but the center of circulation persisted. Most of the thunderstorms were occurring in bands east of the center of circulation. The bands west of the center consisted primarily of low clouds and showers.
Tropical Depression will move through an area marginally favorable for intensification during the next 24 hours. it will move over water where the Sea Surface Temperatures are near 28°C. So, there will be enough energy in the upper ocean to support some intensification. The upper level trough south of Japan will continue to cause moderate vertical wind shear, but the upper level winds could be weak enough to allow for further intensification. Tropical Depression 04W could strengthen into a tropical storm on Saturday.
Tropical Depression 04W is moving near the southwestern part of a ridge over the North Pacific Ocean. The ridge is steering the depression toward the northwest and that general motion is expected to continue for another day or two. On its anticipated track Tropical Depression 04W is expected to pass near the northernmost Mariana Islands. It could pass near Asuncion Island, the Maug Islands, Supply Reef and Farallon de Pajaros. Tropical Depression 04W could bring gust winds, locally heavy rain and higher waves to those places.