Tropical Depression 10W strengthened into Tropical Storm Maria on Wednesday and a Tropical Storm Warning was issued for Guam. At 5:00 a.m. EDT on Wednesday the center of Tropical Storm Maria was located at latitude 12.7°N and longitude 145.9°E which put it about 95 miles (155 km) southeast of Guam. Maria was moving toward the north-northwest at 8 m.p.h. (13 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 1000 mb. Tropical Storm Warnings were in effect for Guam and Rota. Tropical Storm Watches were in effect for Saipan and Tinian.
The center of circulation in former Tropical Depression 10W became more well organized on Wednesday and the Japan Meteorological Agency designated the system as Tropical Storm Maria. The circulation was still increasing in organization. There was a distinct low level center of circulation. Numerous bands of showers and thunderstorms were revolving around the center of circulation. Storms near the center were generating upper level divergence which was pumping mass away from the tropical storm.
Tropical Storm Maria will move through an environment very favorable for intensification during the next few days. Maria will move over water where the Sea Surface Temperature is near 30°C. Tropical Storm Maria will move under the western end of an upper level ridge that is between two upper level lows which are east and west of the ridge. The upper level winds will be relatively weak and there will be little vertical wind shear. The combination of the ridge and two upper level lows will increase the upper level divergence. Tropical Storm Maria will continue to strengthen. Maria will become a typhoon later this week. It could intensify rapidly once an eye forms and the inner core is well developed.
Tropical Storm Maria is moving around the western end of a subtropical ridge which is steering Maria toward the north-northwest. On its anticipated track the center of Tropical Storm Maria will move near Guam and Rota later today. A general motion toward the northwest is forecast for the next several days. Maria could move in the direction of the Ryukyu Islands at the end of the week.
Tropical Storm Maria will bring gusty winds and heavy rain to the southern Mariana Islands. The strongest winds and heaviest rain will affect Guam and Rota. Gusty winds and heavy rain will also affect Saipan and Tinian. Heavy rain could produce flash floods.
Elsewhere over the Western North Pacific Ocean, Tropical Storm Prapiroon was moving over the Sea of Japan. Prapiroon was bringing wind and rain to the northern Islands of Japan including Hokkaido and Honshu. At 5:00 a.m. EDT on Wednesday the center of Tropical Storm Prapiroon was located at latitude 39.6°N and longitude 135.6°E which put it about 360 miles (585 km) west-southwest of Misawa, Japan. Prapiroon was moving toward the northeast at 25 m.p.h. (40 km/h). The maximum sustained wind speed was 50 m.p.h. (80 km/h) and there were winds gusts to 65 m.p.h. (105 km/h). The minimum surface pressure was 987 mb.
Typhoon Prapiroon brought wind and rain to Kyushu on Monday night. At 11:00 p.m. EDT on Monday the center of Typhoon Prapiroon was located at latitude 32.8°N and longitude 128.6°E which put it about 110 miles (180 km) southwest of Sasebo, Japan. Prapiroon was moving toward the north-northeast at 17 m.p.h. (27 km/h). The maximum sustained wind speed was 80 m.p.h. (130 km/h) and there were wind gusts to 100 m.p.h. (160 km/h). The minimum surface pressure was 968 mb.
Rainbands on the eastern side of Typhoon Prapiroon were moving over parts of Kyushu. Those bands were causing gusty winds and they were dropping locally heavy rain. The circulation of Typhoon Prapiroon was exhibiting the effects of a more midlatitude environment. Drier air was wrapping around the western and southern portions of the typhoon. The bands in those parts of Prapiroon consisted primarily of showers and low clouds. The western portion of the eyewall was also weakening. There were still strong thunderstorms in the eastern half of the eyewall and that was where the strongest winds were occurring. Several bands of showers and thunderstorms on the eastern side of the circulation were revolving around the core of Typhoon Prapiroon.
Typhoon Prapiroon will be moving through an environment that will cause it to weaken. Prapiroon was moving over water where the Sea Surface Temperature was near 26°C. However, it will move over water where the Sea Surface Temperature is near 24°C when it moves north of Japan. An upper level trough west of South Korea will produce southwesterly winds which will cause vertical wind shear. The combination of cooler water and more vertical wind shear will cause Typhoon Prapiroon to weaken to a tropical storm on Tuesday. Prapiroon could begin a transition to an extratropical cyclone because of the effects of the midlatitude environment.
Typhoon Prapiroon was being steered toward the north-northeast by the upper level trough. Stronger westerly winds will steer Prapiroon more toward the northeast when it gets north of Japan. On its anticipated track the center of Typhoon Prapiroon will pass near the northwestern portion of Kyushu. The center of Prapiroon is forecast to pass between south Korean and Japan and then to move over the Sea of Japan. Rainbands on the eastern side of Typhoon Prapiroon will cause gusty winds and drop heavy rain over parts of Kyushu. Heavy could cause flash floods in some locations. Prapiroon could also bring wind and rain to southeastern South Korea and parts of northern Honshu.
Elsewhere over the Western North Pacific Ocean Tropical Depression 10W formed southeast of Guam. At 11:00 p.m. EDT on Monday the center of Tropical Depression 10W was located at latitude 10.6°N and longitude 145.7°E which put it about 205 miles (330 km) south-southeast of Guam. It was moving toward the north-northwest at 6 m.p.h. (10 km/h). The maximum sustained wind speed was 30 m.p.h. (50 km/h) and there were wind gusts to 40 m.p.h. (65 km/h). The minimum surface pressure was 1003 mb. A Tropical Storm Warning was issued for Guam. A Tropical Storm Watch was issued for Tinian and Saipan.