Tropical Storm Yutu formed southeast of the Marianas on Sunday. At 5:00 p.m. EDT on Sunday the center of Tropical Storm Yutu was located at latitude 8.7°N and longitude 156.4°E which put it about 880 miles (1420 km) east-southeast of Guam. Yutu was moving toward the west-northwest 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 1002 mb.
A distinct low level center of circulation developed in an area or thunderstorms northeast of Chuuk and the Japan Meteorological Agency designated the system as Tropical Storm Yutu. The circulation around Yutu was organizing quickly. An inner band of showers and thunderstorms was wrapping around the center of circulation. Other bands of showers and thunderstorms were forming and they were starting to revolving around the center. Storms near the center were producing upper level divergence which was pumping mass away from the tropical storm.
Tropical Storm Yutu will be moving through an environment that is very favorable for intensification. Yutu will move over water where the Sea Surface Temperature is near 30°C. It will move through an environment where the upper level winds are weak and there will little vertical wind shear. Tropical Storm Yutu could strengthen into a typhoon within 36 hours and it could rapidly intensify into the equivalent of a major hurricane within three or four days.
Tropical Storm Yutu will move around the western end of a subtropical ridge over the Western North Pacific Ocean during the next few days. The ridge will steer Yutu toward the northwest during the next two or three days. On its anticipated track Yutu will approach the Marianas in about three days. It will likely be a typhoon by that time.
Tropical Storm In-Fa is near Fananu and it is bringing wind and rain to islands around Chuuk. At 10:00 p.m. EST on Wednesday the center of Tropical Storm In-Fa was located near latitude 8.6°N and longitude 152.0°E which put it about 25 miles (40 km) southeast of Fananu and about 620 miles (1000 km) southeast of Guam. In-Fa was moving toward the northwest at 15 m.p.h. (24 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 982 mb.
A Tropical Storm Watch has been issued for Guam. A Typhoon Warning is in effect for Chuuk lagoon, Losap, Ulul and Fananu.
In-Fa was briefly a typhoon earlier on Wednesday when it had a small, but well formed eye. However, the core of In-Fa weakened slightly and the eye filled with clouds. A small, but circular, area of thunderstorms has intensified in the core of the tropical storm during the past few hours. There are signs that In-Fa may be strengthening again. The environment surrounding Tropical Storm In-Fa is favorable for intensification. It is over water where the Sea Surface Temperature is near 29.5°C. The upper level winds are light and the vertical wind shear is modest. In-Fa could regain typhoon intensity on Thursday and a period of rapid intensification may be possible once the inner core reorganizes.
A subtropical ridge north of In-Fa is steering the tropical storm toward the northwest and that general motion is expected to continue for another two or three days. On its anticipated track the center of In-Fa will pass near Fananu during the next few hours. In-Fa could be south of Guam in about 48 hours.
Tropical Storm In-Fa intensified quickly on Tuesday and it caused watches and warnings to be issued for the area around Chuuk. At 10:00 p.m. EST on Tuesday the center of Tropical Storm In-Fa was located at latitude 6.0°N and longitude 156.3°E which put it about 385 miles (620 km) east-southeast of Fananu and about 985 miles (1590 km) east-southeast of Guam. In-Fa was moving toward the west-northwest 18 m.p.h. (29 km/h). The maximum sustained wind speed was 60 m.p.h. (95 km/h) and there were wind gusts to 75 m.p.h. (120 km/h). The minimum surface pressure was 983 mb. A Typhoon Watch has been issued for Fananu.
The circulation of Tropical Storm In-Fa organized rapidly on Tuesday. A tight core formed in the center of circulation and an eyelike feature appeared on satellite images. A small ring of thunderstorms formed around the eye and a large primary rainband wrapped around the circulation. The circulation became more symmetrical and upper level outflow began to create divergence in most directions.
Tropical Storm In-Fa remains in an environment favorable for intensification. It is over water where the Sea Surface Temperature is near 30°C. The upper level winds are light and the vertical wind shear is modest. In-Fa is likely to continue to intensify and now that an inner core has developed, it could intensify rapidly. In-Fa could become a typhoon on Wednesday and it could become the equivalent of a major hurricane later this week.
A subtropical ridge north of In-Fa is steering the tropical storm toward the west-northwest and that general motion is expected to continue for the rest of the week. On its anticipated track In-Fa will approach Fananu in about 24 hours and it could be a typhoon at that time. In-Fa could be approaching Guam in about three days as a typhoon.
A center of circulation formed in an area of thunderstorms southeast of Pohnpei and the system was designated Tropical Depression 27W (TD 27W). At 10:00 p.m. EST on Monday the center of Tropical Depression 27W was located at latitude 4.7°N and longitude 162.3°E which put it about 360 miles (585 km) east-southeast of Pohnpei. TD 27W was moving to the west at 17 m.p.h. (27 km/h). The maximum sustained wind speed was 30 m.p.h. (50 km/h) and there were gusts to 40 m.p.h. (65 km/h). The minimum surface pressure was 1001 mb.
The circulation of TD 27W is still organizing. A clearly defined low level center of circulation formed near the northern edge of an area of thunderstorms. However, most of the stronger thunderstorms are southwest of the center. Those storms are generating upper level divergence that is expanding south and west of the center.
Tropical Depression 27W is in an environment that favors further intensification. It is over water where the Sea Surface Temperature is near 30°C. An upper level ridge north of TD 27W is producing light easterly winds over the top of the depression. The vertical wind shear is modest, and it should only slow the rate of intensification. Intensification could be slow initially as a stronger inner core forms around the center of circulation. Once the core of the circulation consolidates, then intensification could occur more quickly. TD 27W could become a tropical storm within 24 to 36 hours and it could be a typhoon in three or four days.
A subtropical ridge north of TD 27W is steering the depression toward the west. A gradual turn toward the west-northwest is expected and that general motion is expected to continue for much of the week. On its anticipated track TD 27W could be near Pohnpei in about 24 hours and it could bring tropical storm force winds and heavy rain. The tropical cyclone could be approaching Guam by the end of the week and it could be a typhoon by that time.
Tropical Storm Dolphin moved into a more favorable environment and intensified into a typhoon on Tuesday. At 11:00 p.m. EDT on Tuesday the center of Typhoon Dolphin was located at latitude 10.2°N and longitude 155.8°W which put it about 350 miles east-northeast of Chuuk and about 810 miles east-southeast of Guam. Dolphin was moving toward the west at 8 m.p.h. The maximum sustained wind speed was 75 m.p.h. and there were gusts to 90 m.p.h. The minimum surface pressure was 974 mb.
Dolphin moved closer to the axis of an upper level ridge and the vertical wind shear which was inhibiting its intensification diminished. Since Dolphin is over water where the Sea Surface Temperature is near 29°C, the decreased shear allow it to intensify into a typhoon. Dolphin has a small well organized core circulation with a tiny eye at its center. Spiral bands of thunderstorms radiate out from the center. The upper level outflow produced by those thunderstorms has increased and the removal of mass is allowing the surface pressure to decrease. Dolphin is expected to remain in a region of modest vertical wind shear and further intensification is likely. A period of rapid intensification is possible.
A subtropical ridge is steering Dolphin toward the west. The ridge is expected to steer it toward the west-northwest during the next two or three days. On its anticipated track Dolphin would approach Guam in 48 to 60 hours and it could be a significant typhoon at that time.
Tropical Storm Dolphin turned toward the west on Monday and showed signs of more organization. At 11:00 p.m. EDT on Monday the center of Tropical Storm Dolphin was located at latitude 10.3°N and longitude 158.0°E which put it about 490 miles east-northeast of Chuuk and about 950 miles east-southeast of Guam. Dolphin was moving toward the west at 8 m.p.h. The maximum sustained wind speed was 50 m.p.h. and there were gusts to 65 m.p.h. The minimum surface pressure was 989 mb.
Dolphin is moving over water where the Sea Surface Temperature (SST) is near 29°C. Satellite imagery suggests that the circulation became more symmetrical although many of the stronger thunderstorms are west of the center of circulation. A strong upper level ridge is located northwest of Dolphin and it is generating easterly winds winds over the top of the circulation. The vertical wind shear may be the reason why the stronger thunderstorms are west of the center. The upper level ridge is also contributing to an outflow channel to the southwest of Dolphin which cold pump out more mass. The vertical wind shear is inhibiting the intensification of Dolphin. However, as the tropical storm moves farther west, it could move into an area where the upper level winds are lighter. Given the warm SSTs, a decrease in shear would lead to more intensification.
A subtropical ridge is expected to steer Dolphin toward the west during the next two or three days. A turn toward the west-northwest will be possible later in the week if a weakness develops in the ridge. On the anticipated track Dolphin could approach Guam in 48 to 60 hours and it could be a typhoon by that time.
The active period over the tropical Western North Pacific Ocean continues with the development of another tropical cyclone south of Pohnpei. At 8:00 p.m. EDT on Wednesday the center of Tropical Depression 07W was located at latitude 4.4°N and longitude 156.8°E which put it about 160 miles south-southeast of Pohnpei. The tropical depression was stationary. The maximum sustained wind speed was 35 m.p.h. and there were gusts to 50 m.p.h. The minimum surface pressure was 1004 mb.
A low level circulation center formed within a broad area of thunderstorms and the system was classified as Tropical Depression 07W. The strongest thunderstorms are mainly located in the northwestern part of the circulation. An upper level ridge located east of the depression is generating southeasterly winds over the top of it which is producing modest vertical wind shear. The wind shear is the probably reason why most of the thunderstorms are northwest of the center of circulation. The wind shear will also limit the rate of intensification during the next day or two. Eventually the depression is expected to move farther west into an area with less wind shear and it could intensify more quickly.
Tropical Depression 07W is located near the western end of a subtropical ridge and the steering currents are relatively weak. It may not move much for the next 12 to 24 hours. Later this week the ridge is expected to strengthen and steer the depression toward the west-northwest. On its projected track the depression could approach Pohnpei in two or three days.