Category Archives: Western North Pacific

Western Pacific Typhoons and Tropical Storms

Tropical Storm Maysak (04W) Forms East of Chuuk

An area of thunderstorms, that generated mesoscale vortices during the past several days developed a persistent center of circulation on Friday and was classified as Tropical Storm Maysak (04W).  At 11:00 p.m. EDT on Friday the center of Tropical Storm Maysak was located at latitude 7.6°N and longitude 154.9°E which put it about 200 miles east of Chuuk and about 800 miles east-southeast of Guam.  Maysak was moving toward the west at 12 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.

Maysak formed over very warm Sea Surface Temperatures, but moderate upper level easterly winds were causing vertical wind shear and kept shearing the top off the circulation.  When the system moved further west, it moved into an area where the upper level winds were not as strong and a center of circulation develop and persisted.  The organization of the circulation has increased during the past 12 hours and Maysak has been intensifying.  It is expected to take a westerly track which would keep it in an area where the upper level winds should not be too strong.  Steady intensification is expected and rapid intensification is possible.  Maysak could become a typhoon in 24 hours and it could become the equivalent of a major hurricane in three or four days.

A subtropical ridge is steering Maysak toward the west and it is expected to keep steering it in that direction during the next few days.  The projected track takes Maysak very near Chuuk during the next 18 to 24 hours.  In a few days it is projected to pass between Guam and Yap and head in the general direction of the northern Philippines.

 

Wind Shear Still Affecting Tropical Storm Bavi

Strong southerly winds in the upper levels are creating vertical wind shear over Tropical Storm Bavi.  At 11:00 p.m. EDT on Sunday the center of Tropical Storm Bavi was located at latitude 13.4°N and longitude 140.7°W which put it about 250 miles west of Guam and about 1070 miles east of the Philippines.  Bavi was moving toward the west at 22 m.p.h.  The maximum sustained wind speed was 45 m.p.h. and there were wind gusts to 55 m.p.h.  The minimum surface pressure was 993 mb.

A strong upper level ridge east of Bavi is generating brisk southerly winds over the top of the circulation.  Those winds are causing most of the thunderstorms to occur north of the center of circulation.  The structure of the cyclone also appears to be tilted toward the north.  The poor organization of the circulation is preventing it from intensifying.  If the upper level winds do not decrease, it will be difficult for Bavi to organize further.

A subtropical ridge to the north of Bavi is steering it toward the west.  This general motion is expected to continue for the next few days.  The projected track would bring Bavi or its remnants near the Philippines in a few days.

Tropical Storm Bavi Nearing Guam

Tropical Storm Bavi is moving rapidly toward Guam.  At 11:00 p.m. EDT on Saturday the center of Tropical Storm Bavi was located at latitude 13.8°N and longitude 148.7°E which put it about 100 miles east-northeast of Guam.  Bavi was moving toward the west at 18 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.

Bavi is moving over water where the Sea Surface Temperatures are around 27.5°C.  So, there is sufficient energy to support intensification.  Moderate easterly winds in the upper levels are generating vertical wind shear over the circulation.  Most of the thunderstorms have been located in the western half of the circulation.  However, recent satellite imagery indicates that there may be more thunderstorms forming near the core of the circulation.  The rapid movement of the storm and the wind shear are likely to limit potential intensification.

A subtropical ridge to the north of Bavi is steering it rapidly to the west and that motion is expected to continue.  Bavi will move  near Guam within a few hours and the core of the circulation could pass near Rota, Tinian and Saipan.  It is likely to bring gusty winds and locally heavy rains as it passes.  The subtropical ridge is expected to steer Bavi or its remnants toward the Philippines during the next few days.

Tropical Storm Bavi Moving Toward Guam

Tropical Storm Bavi continued to move rapidly toward the west-northwest toward Guam on Friday.  At 5:00 p.m. EDT on Friday the center of Tropical Storm Bavi was located at latitude 10.7°N and longitude 157.6°E which put it about 880 miles east-southeast of Guam.  Bavi was moving toward the west-northwest at 17 m.p.h.  The maximum sustained wind speed was 45 m.p.h. and there were gusts to 60 m.p.h.  The minimum surface pressure was 989 mb.

Strong easterly winds in the upper levels are creating vertical wind shear and are inhibiting intensification of Bavi.  The wind shear is also causing most of the thunderstorms to be located on the western side of the circulation.  Thus, Bavi is not well organized at the current time.  However, Bavi is moving over warm Sea Surface Temperatures and it could strengthen slowly as it moves farther west, if the wind shear decreases.

A strong subtropical ridge to the north of Bavi is steering it rapidly westward.  Bavi could be in the vicinity of Guam in about 48 hours.  The ridge is expected to continue to steer Bavi westward after it moves past Guam and it could approach the Philippines in a few days.

Tropical Storm Bavi Forms South of Kwajalein

A fourth tropical cyclone formed in the active region over the western Pacific and Australian region.  A low level circulation center developed in an elongated area of thunderstorms south of Kwajalein and the system was classified as Tropical Storm Bavi.  At 11:00 p.m. EDT on Wednesday the center of Tropical Storm Bavi was located at latitude 7.2°N and longitude 166.7°E which put it about 40 miles southwest of Kwajaein, about 410 miles east-southeast of Ujelang and about 1470 miles east of Guam.  Bavi was moving toward the west at 18 m.p.h.  The maximum sustained wind speed was 40 m.p.h. and there were gusts to 50 m.p.h.  The minimum surface pressure was 996 mb.

The circulation around Bavi is stretched out in the east to west direction and most of the convection and stronger winds are on the northern side of the circulation.  The rapid forward speed is generating vertical wind shear and it is inhibiting the organization around the center of circulation.  Brisk easterly winds in the upper levels are adding to the wind shear.  Bavi is moving over warm Sea Surface Temperatures and it could intensify if the forward motion slows and the wind shear decreases.

A subtropical ridge is steering Bavi in a westerly direction.  The ridge is expected to continue to steer Bavi toward the west or west-northwest over the next several days.   The projected track of Bavi could bring it near Guam in about four days.

Higos Weakening Rapidly East of Saipan

After intensifying rapidly into a strong but small typhoon on Monday, vertical wind shear caused Higos to begin a rapid weakening trend on Tuesday.  At 11:00 p.m. EST on Tuesday the center of Typhoon Higos was located at latitude 15.3°N and longitude 152.9°E which put it about 450 miles east of Saipan and about 880 miles west-southwest of Wake Island.  Higos was moving toward the west-northwest at 7 m.p.h.  The maximum sustained wind speed was 80 m.p.h. and there were gusts to 90 m.p.h.  The minimum surface pressure was estimated to be 974 mb.

Strong southwesterly winds in the upper levels are blowing over the top of Higos.  Those strong winds have blown the upper half of the circulation off to the northeast of the lower half of the circulation.  The lower portion of the circulation consists of a tight center with spiral bands of shallower clouds rotating around the center.  The wind shear is preventing deep thunderstorms from forming near the center and it is causing Higos to weaken rapidly.  Unless the shear lets up, which is unlikely, the lack of deep convection to remove mass will cause the surface pressure to increase and the circulation to spin down.

Since Higos consists primarily of a lower level circulation it is likely to be steered by winds in the lower portion of the atmosphere.  A subtropical ridge to the east of Higos is likely to steer it to the north-northwest until the wind shear causes it to spin down.

 

Typhoon Higos Maintaining Intensity Well East of Guam

The organization of Typhoon Higos improved on Monday.  At 11:00 p.m. EST on Monday the center of Typhoon Higos was located at latitude 13.7°N and longitude 154.7°E which put it about 710 miles east of Guam and about 870 miles west-southwest of Wake Island.  Higos was moving toward the northwest at 9 m.p.h.  The maximum sustained wind speed was 95 m.p.h. and there were gusts to 115 m.p.h.  The minimum surface pressure was 967 mb.

The circulation around Higos remains in an area where the upper level winds are not too strong and the wind shear is in the light to moderate range.  An eye has developed at the center of circulation which is evident on both infrared and visible satellite imagery.  The eye is surrounding by a tight symmetrical ring of thunderstorms.  It has the appearance of a well organized circulation.  Upper level outflow continues and it is especially strong on the northeast side of Higos.  The typhoon also remains over warm Sea Surface Temperatures and so the environment could support some further intensification on Tuesday.  As Higos moves farther north, it will begin to be affected by stronger upper level westerly winds.  The stronger winds will create more wind shear and weaken Higos.

Higos is moving around the western end of a subtropical ridge, which is steering it toward the northwest.  As it gets farther north, the upper level westerly winds will being to push it toward the northeast.  Higos is expected to weaken as it moves northwest of Wake Island.

 

Higos Intensfies Into a Typhoon

Tropical Storm Higos intensified into a typhoon on Sunday.  At 11:00 p.m. EST on Sunday the center of Typhoon Higos was located at latitude 12.3°N and longitude 156.4°E which put it about 780 miles east of Guam.  It was moving toward the west-northwest at 3 m.p.h.  The maximum sustained wind speed was 85 m.p.h. and there were gusts to 100 m.p.h.  The minimum surface pressure was 967 mb.

Higos has been moving slowly through an area where the vertical wind shear was not too strong.  Thunderstorms around the center of circulation supported strong upper level divergence, which pumped out large quantities of mass.  A well developed upper level outflow channel to the northeast enhanced the flow of mass away from the system.  Those processes allowed the surface pressure to decrease and the wind speeds to increase on Sunday.  Higos remains over warm Sea Surface Temperatures and further intensification is possible on Monday.  Eventually, when it moves farther north, Higos will move into an area of stronger wind shear and weaken.

Higos is moving near the western end of a subtropical ridge.  It is in an area of weak steering winds, and Higos is moving slowly.  The increased intensity and vertical height of the circulation make it more likely that Higos will move toward the north as it reaches the western end of the subtropical ridge.  The guidance from numerical models has increased the probability of this track.

 

Tropical Storm Higos Forms East of Guam

A center of circulation consolidated within a large area of thunderstorms centered about 900 miles east of Guam and the system was designated as Tropical Storm Higos.  At 10:00 p.m. EST on Saturday the center of Tropical Storm Higos was located at latitude 12.1°N and longitude 157.4°E which put it about 480 miles northeast of Fananu and about 850 miles east of Guam.  Higos was moving toward the north-northwest at 7 m.p.h.  The maximum sustained wind speed was 45 m.p.h. and there were wind gusts to 60 m.p.h.  The minimum surface pressure was 993 mb.

Higos was moving over warm Sea Surface Temperatures.  Satellite imagery indicated that upper level divergence was well developed and there appeared to be an outflow channel to the northeast.  As the divergence pumped out mass, the surface pressure decreased and the wind speeds increased.  A spiral band of thunderstorms wrapped around the center of circulation and the system displayed increased organization.  Higos has the potential to intensify during the next 24 to 48 hours and it could possible become a typhoon.  Later in the week stronger upper level winds are expected to increase the vertical wind shear and weaken Higos.

Higos was near the western end of a subtropical ridge of high pressure which was steering it toward the northwest.  The subtropical ridge is expected to continue to steer the storm toward the northwest in the short term.  Over the longer term the track of Higos will depend to some extent on how strong it becomes.  If it intensifies more, Higos will be affected more strongly by upper level westerly winds located farther north.  Those winds would cause Higos to take a more northerly track.  If Higos remains weaker, then it could be less affected by the upper level westerlies and it might take a track farther south.  Guidance from numerical models is split between a more northerly and a more westerly track.

 

Tropical Storm Mekkhala Moving Through the Philippines

Tropical Storm Mekkhala is moving through the northern Philippines.  At 11:00 p.m. EST on Saturday the center of Tropical Storm Mekkhala was located at latitude 13.9°N and longitude 123.0°E which put it near Daet and about 150 miles east-southeast of Manilla.  Mekkhala was moving toward the northwest at 11 m.p.h.  The maximum sustained wind speed was 40 m.p.h. and there were gusts to 50 m.p.h.  The minimum surface pressure was 996 mb.

Mekkhala crossed over northern parts of Samar on Saturday and the center is near the southeastern portion of Luzon.  The islands disrupted parts of the circulation in the lower levels and Mekkhala weakened throughout the day.  Thunderstorms have been redeveloping in the part of the circulation over Lamon Bay and Mekkhala continues to be a tropical storm.  Divergence continues in the upper portion of the circulation and the wind shear remains at a moderate level.  While the atmospheric and oceanic environment would support intensification, if the center moves across Luzon further weakening is likely.

Mekkhala is near the western end of a subtropical ridge which has been steering the system toward the northwest.  If deep convection continues, then the ridge could continue to steer it toward the northwest.  However, if the system weakens to the point where only shallow convection exists, then it could be steered more toward the west by the lower level flow.

The relatively slow movement of Mekkhala continues the potential for locally heavy rainfall, flooding and mudslides.