Tropical Depression 27W intensified into Tropical Storm Ma-On east of the Northern Marianas on Thursday. At 10:00 a.m. EDT on Thursday the center of Tropical Storm Ma-On was located at latitude 17.7°N and longitude 153.7°E which put it about 405 miles (655 km) south-southeast of Minami Tori Shima. Ma-On was moving toward the west at 15 m.p.h. (24 km/h). The maximum sustained wind speed was 40 m.p.h. (65 km/h) and there were wind gusts to 50 m.p.h. (80 km/h). The minimum surface pressure was 1003 mb.
More thunderstorms developed near the center of a system originally designated Tropical Depression 27W and the Japan Meteorological Agency named it Tropical Storm Ma-On on Thursday. Although many of the thunderstorms are still developing east of the center of circulation, a few stronger thunderstorms are forming around the center. The thunderstorms around the center are beginning to generate upper level divergence which is pumping out mass. Some additional rainbands appear to be forming in the eastern half of the circulation.
Tropical Storm Ma-On is moving through an environment that is favorable for intensification. Ma-On is moving over water where the Sea Surface Temperature is near 30°C. Ma-On is moving under the western end of an upper level ridge. The upper level winds in that part of the ridge are not too strong and the ridge may be enhancing upper level divergence. Tropical Storm Ma-On could intensify during the next day or so. When Ma-On gets farther west, it will approach an upper level trough moving off of Asia. There are stronger southwesterly winds on the eastern side of the trough and the vertical wind shear will increase at that time.
Tropical Storm Ma-On is moving along the southwestern end of a subtropical high pressure system. The subtropical high is expected to steer Ma-On in a general west-northwesterly direction during the next two or three days. On its anticipated track Tropical Storm Ma-On could approach the northernmost Marianas in about 36 hours. It could bring gusty winds and locally heavy rain.