Category Archives: Western North Pacific

Western Pacific Typhoons and Tropical Storms

Tropical Storm Nanmadol Forms Southeast of Taiwan

Tropical Storm Nanmadol formed southeast of Taiwan on Saturday.  At 8:00 p.m. EDT on Saturday the center of Tropical Storm Nanmadol was located at latitude 20.7°N and longitude 127.1°E which put it about 475 miles (765 km) southeast of Taipei, Taiwan.  Nanmadol was moving toward the northwest at 24 m.p.h. (35 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 center of circulation consolidated rapidly on Saturday in an area of thunderstorms southeast of Taiwan.  A primary band of showers and thunderstorms wrapped around the northern and western side of the circulation.  Other bands of showers and thunderstorms developed in the northern half of the circulation.  The thunderstorms near the center began to generate upper level divergence which pumped out mass to the north of the tropical storm.

Tropical Storm Nanmadol will move through an area favorable for intensification during the next 24 hours.  Nanmadol will move over water where the Sea Surface Temperature is near 30°C.  An upper level ridge northeast of Nanmadol is producing southeasterly winds which are blowing toward the top of the tropical storm, but there is little vertical wind shear.  Tropical Storm Nanmadol is likely to intensify on Sunday.  When Nanmadol moves farther north, it will move over cooler water and it will be effected by the upper level westerly winds in the middle latitudes.  Cooler water and more vertical wind shear will cause Nanmadol to start to weaken at that time.

Tropical Storm Nanmadol is moving around the western end of a subtropical ridge which is steering it quickly toward the northwest.  Nanmadol will move in a general north-northwesterly direction on Sunday.  It will turn toward the northeast in 24 to 36 hours when it begins to be steered by the mid-latitude westerlies.  On its anticipated track Tropical Storm Nanmadol could approach the southernmost Ryukyu Islands including Ishigaki Jima in about 12 hours.  The center is expected to pass west of Okinawa.  Tropical Storm Nanmadol could approach Kyushu in a couple of days.  An intensifying Tropical Storm Nanmadol will bring gusty winds and locally heavy rain to the southernmost Ryukyu Islands.

Tropical Storm Merbok Makes Landfall Near Hong Kong

Tropical Storm Merbok made landfall near Hong Kong on Monday.  At 5:00 p.m. EDT on Monday the center of Tropical Storm Merbok was located at latitude 23.5°N and longitude 114.9°E which put it about 55 miles (85 km) north-northeast of Hong Kong.  Merbok was moving toward the north at 11 m.p.h. (17 km/h).  The maximum sustained wind speed was 45 m.p.h. (75 km/h) and there were wind gusts to 60 m.p.h. (95 km/h).  The minimum surface pressure was 1005 mb.

Tropical Storm Merbok intensified before it made landfall and the maximum sustained wind speed was around 55 m.p.h. (85 km/h) at the time of landfall.  Merbok began to weaken after landfall and the strongest winds are now occurring in bands over the the open water.  Merbok is producing locally heavy rain in bands east of the center if circulation.  The heavy rains represent the greatest risk and flooding is possible over parts of eastern China.  Merbok is a fairly small tropical storm and the heavier rain will fall primarily to the east of the track of Merbok.  Merbok should gradually spin down as it moves farther inland.

Tropical Storm Merbok Moves Closer to China

Tropical Depression 04W intensified into Tropical Storm Merbok on Sunday as it moved closer to the coast of China.  At 5:00 p.m. EDT on Sunday the center of Tropical Storm Merbok was located at latitude 19.9°N and longitude 115.7°E which put it about 220 miles (360 km) south-southeast of Hong Kong.  Merbok was moving toward the north-northwest at 16 m.p.h. (26 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 999 mb.

The structure of Tropical Storm Merbok is asymmetrical.  Most of the thunderstorms are occurring east and south of the center of circulation.  A primary rainband curves about halfway around the southeastern side of the center.  Additional bands of showers and thunderstorms exist outside the core in southeastern half of Merbok.  There are bands in the northwestern half of the circulation but they consists primarily of low clouds and showers.  The thunderstorms in the primary rainband are producing upper level divergence which is pumping out mass to the south of Tropical Storm Merbok.

Tropical Storm Merbok is moving through an environment that is marginally favorable for intensification.  It is moving over water where the Sea Surface Temperature is near 29°C.  Merbok is moving under the eastern end of an upper level ridge which is producing northerly winds which are blowing toward the top of the tropical storm.  Those northerly winds are creating moderate vertical wind shear, but they are also enhancing the upper level divergence to the south of Merbok.  Tropical Storm Merbok appears to be pulling some drier air from China into the northwestern part of the circulation.  The combination of moderate vertical wind shear and drier air could be the reason for the asymmetrical distribution of thunderstorms.

Tropical Storm Merbok has a chance to intensify a little more before it makes landfall.  The effects of the moderate vertical wind shear and drier air should limit any intensification and Merbok is likely to remain a tropical storm until it makes landfall.

Merbok is moving around the western end of a subtropical ridge which is steering the tropical storm toward the north-northwest.  That general motion is expected to continue for another day or so.  On its anticipated track the center of Tropical Storm Merbok will reach the coast of China between Hong Kong and Shantou in 12 to 18 hours.  Tropical Storm Merbok will bring gust winds and locally heavy rain.  When Merbok moves inland over eastern China, it will reach the westerly winds in the middle latitudes and those winds will turn the tropical storm toward the east.

Tropical Depression 04W Forms West of Luzon

Tropical Depression 04W formed west of Luzon on Saturday.  At 11:00 p.m. EDT on Saturday the center of Tropical Depression 04W was located at latitude 16.6°N and longitude 116.8°E which put it about 430 miles (690 km) south-southeast of Hong Kong.  The depression was moving toward the northwest at 10 m.p.h. (16 km/h).  The maximum sustained wind speed was 35 m.p.h. (55 km/h) and there were wind gusts to 45 m.p.h. (75 km/h).  The minimum surface pressure was 1006 mb.

An area of thunderstorms moved west-northwestward across the Philippines and a circulation slowly consolidated around a distinct center.  The center of circulation became well enough defined on Saturday to cause the system to be classified as Tropical Depression 04W.  The inner core of the depression is still organizing.  A band of thunderstorms wrapped around the western and southern sides of the center of circulation.  Additional bands of showers and thunderstorms developed in other parts of the depression.  The area of showers and thunderstorms southwest of the center began to generate upper level divergence which pumped mass away from the depression.

Tropical Depression 04W will be moving through an environment that is favorable for intensification.  The depression will move over water where the Sea Surface Temperature is near 30°C.  The depression is moving under the eastern end of an upper level ridge.  The ridge is producing northerly winds which are blowing toward the top of the circulation.  The vertical wind shear may be part of the reason why there are more thunderstorms south of the center of circulation, but the shear is not strong enough to prevent intensification.  Tropical Depression 04W is expected to intensify into a tropical storm during the next 24 hours.

Tropical Depression 04W is moving around the western end of a subtropical ridge which is steering it toward the northwest.  A general northwesterly motion is expected for another 36 to 48 hours.  A turn toward the east will occur after that time.  On its anticipated track Tropical Depression 04W could be near Hong Kong in about 36 hours.  Tropical Depression 04W will have strengthened into a tropical storm by that time and there is a chance it could intensify into a typhoon by the time it nears the coast of China.

Tropical Cyclone Frances Develops North of Western Australia

An area of low pressure northwest of Western Australia developed into Tropical Cyclone Frances on Thursday.  At 10:00 a.m. EDT on Thursday the center of Tropical Cyclone Frances was located at latitude 11.0°S and longitude 128.3°E which put it about 255 miles (410 km) north-northeast of Kalumburu, Australia.  Frances was moving toward the west-southwest at 12 m.p.h. (19 km/h).  The maximum sustained wind speed was 50 m.p.h. (80 km/h) and there were wind gusts to 65 m.p.h. (110 km/h).  The minimum surface pressure was 997 mb.

The organization of Tropical Cyclone Frances improved significantly during the past 24 hours.  A well organized center of circulation developed at the surface.  A primary rainband wrapped about two-thirds of the way around the southern and western sides of the center.  Additional bands of showers and thunderstorms formed in the outer portions of the circulation.  Thunderstorms near the core of the circulation generated upper level divergence which was pumping mass away to the south of the tropical cyclone.  Frances is a fairly small tropical cyclone and winds to tropical storm force only extend out about 100 miles (160 km) from the center.

Tropical Cyclone Frances will move through an environment that will be favorable for intensification during the next 24 to 36 hours.  Frances will move over water where the Sea Surface Temperature is near 30°C while is moves across the Timor Sea.  An upper level ridge east of Tropical Cyclone Frances is producing northeasterly winds which are blowing toward the top of the circulation.  Vertical wind shear may be the reason that the primary rainband wrapped around the southern and western sides of the center.  However, the vertical shear does not appear to be strong enough to significantly affect the upper level divergence.  Frances is likely to intensify during the next day or so.  Eventually, Tropical Cyclone Frances will move into an area where there are strong upper level northwesterly winds.  A significant increase in vertical wind shear should weaken Frances when that occurs.

A subtropical ridge to the east of Frances is steering the tropical cyclone toward the west-southwest.  A general motion toward the west-southwest is expected to continue during the next few days.  On its anticipated track the center of Tropical Cyclone Frances is forecast to stay north of the coast of Western Australia.  However, any southward deviation of the track could bring stronger winds closer to the coast.

TD 03W Intensifies Into Tropical Storm Muifa

Tropical Depression 03W intensified into Tropical Storm Muifa on Tuesday as it moved slowly northwest of Yap.  At 11:00 p.m. EDT on Tuesday the center of Tropical Storm Muifa was located at latitude 13.3°N and longitude 134.6°E which put it about 335 miles (540 km) northwest of Yap.  Muifa was moving toward the west-northwest at 4 m.p.h. (6 km/h).  The maximum sustained wind speed was 45 m.p.h. (75 km/h) and there were wind gusts to 60 m.p.h. (95 km/h).  The minimum surface pressure was 1000 mb.

The circulation of Tropical Cyclone Muifa is not well organized.  There is a well defined low level center.  However, almost all of the showers and thunderstorms are in a cluster east of the low level center.  There are almost no showers and thunderstorms in the western half of the circulation.  Few well defined rainbands are evident in the eastern half of the circulation.  The cluster of thunderstorms east of the center of circulation is generating some upper level divergence which appears to be pumping mass out to the northwest of the tropical storm.

Tropical Storm Muifa will be moving through an environment that will be marginally favorable for intensification.  Muifa will move over water where the Sea Surface Temperature will be near 29.5°C.  A subtropical ridge east of Muifa is producing easterly winds which are blowing toward the tropical storm.  Tropical Storm Muifa is currently south of the upper level westerly winds in the middle latitudes.  Muifa is currently in a region where the upper level winds are weaker and the vertical wind shear is moderate.  Areas of stronger vertical wind shear surround the tropical storm.  Tropical Storm Muifa could intensify a little more during the next 24 hours before it reaches an area where the shear is stronger.

Tropical Storm Muifa is moving around the western end of the subtropical ridge to its east and the steering winds are weak.  As a result Muifa is moving slowly toward the west-northwest.  A gradual turn toward the north is forecast as Tropical Storm Muifa moves around the end of the ridge.  Muifa will reach an area of westerly winds as it moves farther north and the tropical storm is forecast to recurve toward the northeast.

Tropical Depression 03W Forms Northwest of Yap

Tropical Depression 03W formed northwest of Yap on Monday.  At 11:00 p.m. EDT on Monday the center of Tropical Depression 03W was located at latitude 12.5°N and longitude 135.2°E which put it about 260 miles (420 km) northwest of Yap.  The depression was moving toward the west at 10 m.p.h. (16 km/h).  The maximum sustained wind speed was 35 m.p.h. (55 km/h) and there were wind gusts to 45 m.p.h. (75 km/h).  The minimum surface pressure was 1003 mb.

A cluster of thunderstorms developed southeast of the Marianas during the weekend.  The cluster moved slowly toward the west-northwest and the circulation gradually exhibited signs of greater organization.  Satellite imagery indicated that a center of circulation formed in the lower levels of the circulation and the system was designated as Tropical Depression 03W on Monday.

The circulation of Tropical Depression 03W is still organizing.  Although there is a distinct low level center, the distribution of showers and thunderstorms is asymmetrical.  Many of the showers and thunderstorms are forming east of the center of circulation.  There are few showers and thunderstorms in the western half of the circulation.  Thunderstorms just to the east of the center of the circulation are generating some upper level divergence that is pumping out mass to the west and north of the center of circulation.

Tropical Depression 03W will be moving through an environment that will be somewhat favorable for intensification.  It will move over water where the Sea Surface Temperature will be near 30°C.  A ridge of high pressure east of the depression is producing easterly flow that is blowing toward the depression.  The flow may be pushing the lower part of the circulation to the west of the middle and upper portions.  Vertical wind shear could be an inhibiting factor.  Some intensification is forecast during the next day or two and the depression could intensify into a tropical storm.

The ridge of the depression is steering it toward the west.  The depression is expected to turn toward the northwest when it reaches the western end of the depression in a day or so.

Tropical Depression 02W Forms East of the Philippines

Tropical Depression 02W formed east of the Philippines on Friday.  At 11:00 a.m. EDT on Friday the center of Tropical Depression 02W was located at latitude 10.7°N and longitude 128.1°E which put it about 190 miles (305 km) east-southeast of Dolores, Philippines.  Tropical Depression 02W was moving toward the west-northwest at 13 m.p.h. (21 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 1004 mb.

The circulation of Tropical Depression 02W is organizing around a low level center east of Samar and Leyte.  Thunderstorms were developing near the center of circulation and several spiral bands were developing farther away from the center.  The thunderstorms near the center of circulation were just beginning to generate upper level divergence.

Tropical Depression 02W will move through an environment that will be favorable for intensification during the next 18 to 24 hours.  It will move over water where the Sea Surface Temperature is near 30°C.  An upper level ridge located east of Tropical Depression 02W is producing easterly winds that are blowing toward the depression, but the vertical wind shear is minimal.  The combination of warm SSTs and little vertical wind shear could allow Tropical Depression 02W to organize quickly and it could become a tropical storm before it reaches the Philippines.

A subtropical ridge is steering Tropical Depression 02W toward the west-northwest and that general motion is expected to continue for the next several days.  On its anticipated track Tropical Depression 02W will move across the Central Philippines during the weekend.  Tropical Depression 02W could bring gusty winds and heavy rain to portions of Samar, Leyte, Cebu, Panay, Mindoro and southern Luzon.  Heavy rain could create a risk for mudslides in some areas.

Tropical Depression 01W Redevelops East of Vietnam

More thunderstorms developed on Saturday around the circulation previously designated Tropical Depression 01W earlier this week when it moved through the southern Philippines.  At 10:00 p.m. EST the center of Tropical Depression 01W was located at latitude 9.4°N and longitude 109.1°E which put it about 220 miles (355 km) east-southeast of Ho Chi Minh City, Vietnam.  The depression was moving toward the west at 6 m.p.h. (10 km/h).  The maximum sustained wind speed was 35 m.p.h. (55 km/h) and there were wind gusts to 45 m.p.h. (75 km/h).  The minimum surface pressure was 1002 mb.

After persisting mainly as a low level circulation during the past few days as it moved westward across the South China Sea, more thunderstorms developed in the depression on Saturday.  Most of the thunderstorms developed in bands north and west of the center of circulation.  There were bands of low clouds and showers in the southeastern portion of the circulation. The depression has a well defined low level center of circulation.  Thunderstorms were starting to generate some upper level divergence which was pumping mass away to the northwest of the depression.

The depression will be moving through an environment that is marginal for intensification.  It will be moving over water where the Sea Surface Temperature is near 26°C to 27°C.  So, there will be enough energy in the upper ocean to support intensification.  An upper level ridge to the east of the depression is generating southeasterly winds which are blowing across the top of the circulation.  The moderate vertical wind shear will inhibit intensification.  If the shear does not increase, the depression could maintain its intensity or strengthen slightly during the next 24 hours.

A ridge north of the depression is steering it toward the west and that general motion is expected to continue for another day or two.  On its anticipated track the depression will move toward the southernmost part of Vietnam.  The depression could bring locally heavy rain to southern Vietnam.  The rain could be heavy enough to cause flooding in some areas.

Tropical Depression 01W Forms Near Mindanao

A center of circulation formed within a cluster of thunderstorms east of Mindanao on Saturday and the system was designated Tropical Depression 01W.  At 10:00 p.m. EST on Saturday the center of Tropical Depression 01W was located at latitude 9.2°N and longitude 126.5°E which put it about 200 miles (320 km) east-southeast of Cebu, Philippines.  The depression was moving toward the northwest at 10 m.p.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 1000 mb.

Although there is a distinct center of circulation in Tropical Depression 01W, the distribution of thunderstorms is asymmetrical.  Most of the stronger thunderstorms are forming in the northern half of the circulation and there are few thunderstorms in the southern half of the circulation.  The thunderstorms in the northern half of the circulation are generating upper level divergence that is pumping out mass toward the northeast and northwest of the tropical depression.

Tropical Depression 01W will be moving through an oceanic and atmospheric environment that is somewhat favorable for intensification.  It will move over water where the Sea Surface Temperature is near 28°C.  An upper level ridge is generating southeasterly winds which are blowing across the top of the depression, but the vertical wind shear is not too strong.  However, the center of Tropical Depression 01W will move over some of the islands of the southern Philippines.  Increases friction and high topography will disrupt the circulation each time the center moves over land.  The intermittent passages overland will cause weakening and the intensity of Tropical Depression 01W is likely to fluctuate during the next several days.

A subtropical ridge north of the depression is steering it toward the northwest.  The ridge is forecast to strengthen and it is predicted to steer Tropical Depression 01W in a general westerly direction during the next several days.  On its anticipated track the center of Tropical Depression 01W will pass near northern Mindanao, Siargao Island, Dinogat Island, Leyte, Bohol Island, Cebu, Negros, and Panay Island.

Heavy rain associated will be the greatest threat with Tropical Depression 01W.  The heaviest rain will fall north of where the center moves.  The heavy rain could cause flooding and mudslides,