Tag Archives: WP11

Tropical Storm Nesat Forms Southeast of Taiwan

Tropical Storm Newsat formed southeast of Taiwan on Wednesday.  At 11:00 p.m. EDT on Wednesday the center of Tropical Storm Nesat was located at latitude 18.0°N and longitude 127.5°E which put it about 620 miles (1000 km) southeast of Taipei, Taiwan.  Nesat was moving toward the north at 6 m.p.h. (10 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 988 mb.

A well organized surface circulation formed in an area of thunderstorms southeast of Taiwan on Wednesday.  A strong cluster of thunderstorms formed south of the center of circulation.  Additional bands of showers and thunderstorms developed in the western and southern portions of Tropical Storm Nesat.  There were few thunderstorms in the eastern half of the circulation.  More thunderstorms appeared to be forming near the core of the circulation in recent hours.  The thunderstorms in the core were generating upper level divergence which was pumping out mass.

Tropical Storm Nesat will be moving through an area that is favorable for intensification.  Nesat will move over water where the Sea Surface Temperature is near 31°C.  Tropical Storm Nesat is beneath the northeastern part of an upper level ridge.  The ridge is producing northeasterly winds which are blowing toward the top of the circulation.  Those winds are causing some vertical wind shear and the shear could be the reason for the asymmetrical distribution of thunderstorms.  Tropical Storm Nesat could move under the axis of the upper level ridge where the winds are weaker.  In that case the shear would be less and Nesat could intensify more quickly.  Tropical Storm Nesat is likely to intensify into a typhoon during the next 24 hours.

Tropical Storm Nesat is moving around a weak area in a subtropical ridge, which is allowing the tropical storm to move toward the north.  The ridge is forecast to strengthen and when that happens it will steer Nesat more toward the west.  On its anticipated track Tropical Storm Nesat could approach Taiwan in about three days.  Nesat could be a strong typhoon when it nears Taiwan.

Elsewhere in the Western North Pacific Typhoon Noru has turned back toward the west.  At 11:00 p.m. EDT on Wednesday the center of Typhoon Noru was located at latitude 30.6°N and longitude 151.2°E which put it about 770 miles (1240 km) east-northeast of Iwo To.  Noru was moving toward the west at 19 m.p.h. (31 km/h).  The maximum sustained wind speed was 75 m.p.h. (120 km/h) and there were wind gusts to 90 m.p.h. (150 km/h).  The minimum surface pressure was 978 mb.

A subtropical ridge north of Typhoon Noru is steering the typhoon toward the west.  A general westerly motion is forecast to continue for several more days.  Noru could reach an area of weaker steering winds in a few days and its motion may slow.  On its anticipated track Typhoon Noru could approach Iwo To in three or four days.

Tropical Storm Dianmu Forms Near Hainan Island

A center of circulation developed within a larger cyclonic rotation associated with the monsoon near Hainan Island and the Japan Meteorological Agency classified the system as Tropical Storm Dianmu.  At 5:00 a.m. EDT on Thursday the center of Tropical Storm Dianmu was located at latitude 20.5°N and longitude 109.7°E which put it about 265 miles (430 km) east of Hanoi, Vietnam.  Dianmu was moving toward the west at 10 m.p.h. (16 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 985 mb.

The circulation of Tropical Storm Dianmu consists of a smaller counterclockwise rotation inside a much larger cyclonic flow associated with the monsoonal circulation.  Thunderstorms clustered around the western and southern portion of the smaller counterclockwise rotation and a distinct inner core developed that is separate from the broader center of the monsoonal gyre.  Additional spiral bands formed outside the core.  The thunderstorms are generating upper level divergence, primarily to the south and west of Tropical Storm Diamnu.

Tropical Storm Dianmu is moving through an environment that is favorable for additional strengthening.  It is moving over water where the Sea Surface Temperature is near 31°C.  An upper level ridge centered over China is producing easterly winds which are blowing across the top of Tropical Storm Dianmu.  Those winds are causing moderate vertical wind shear, which is slowing the rate of intensification of the tropical storm.  The proximity of Dianmu to the coast is also slowing the rate of intensification.  Tropical Storm Dianmu has 12 to 18 hours to intensify before it moves over land.

The upper level ridge over China is steering Tropical Storm Dianmu toward the west and that general motion is expected to continue.  On its anticipated track the center of Tropical Storm Dianmu could reach the coast of Vietnam in 12 to 18 hours.  Dianmu could cause some minimal wind damage and storm surge, but heavy rain will be the greatest threat.  Tropical Storm Dianmu could cause flash flooding when it moves inland over Southeast Asia.