A defined center of circulation developed within a cluster of thunderstorms that moved west of the Philippines on Tuesday and the system was designated Tropical Storm Mirinae.  Tropical Storm Mirinae is now moving over Hainan Island and it is bringing heavy rain to the southern portion of the island.  At 5:00 p.m. EDT on Tuesday the center of Tropical Storm Mirinae was located at latitude 19.3°N and 109.4°E which put it about 60 miles (95 km) south-southwest of Haikou, China.  Mirinae was moving toward the west-northwest at 13 m.p.h. (21 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. (90 km/h).  The minimum surface pressure was 996 mb.

An upper level ridge over Asia is producing northeasterly winds which are blowing over the top of Tropical Storm Mirinae.  The moderate vertical wind shear is causing most of the strong thunderstorms to be located in the southern half of the tropical storm.  Those thunderstorms are generating upper level divergence to the south of the center of circulation, but the northeasterly winds are inhibiting the motion of air trying to diverge to the north of Mirinae.

Tropical Storm MIrinae is in an environment that is not overly favorable for intensification.  It is moving over Hainan Island and increased surface friction will slow the circulation.  The moderate vertical wind shear is also a negative factor.  However, when the center of circulation moves west of Hainan Island, it will move over water where the Sea Surface Temperature is near 30°C.  So, some re-intensifcation could occur before Tropical Storm MIrinae makes landfall in Asia.

A subtropical ridge northeast of MIrinae is steering the tropical storm toward the west-northwest and that general motion is expected to continue for another day or so.  On its anticipated track Tropical Storm Mirinae will move over the Gulf of Tongking in a few hours.  The center of Tropical Storm Mirinae could reach the coast of northern Vietnam in about 24 hours.

MIrinae is a minimal tropical storm and it is not likely to intensify a great deal.  Heavy rain and floods are the primary risks associated with Tropical Storm Mirinae.  The heaviest rain is likely to fall near and south of the center of circulation.