Category Archives: Western North Pacific

Western Pacific Typhoons and Tropical Storms

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.

 

Mekkhala Becomes a Typhoon As It Near the Philippines

Tropical Storm Mekkhala intensified rapidly on Friday and it has reached typhoon intensity.  At 3:00 p.m. EST on Friday the center of Mekkhala was located at latitude 10.9°N and longitude 127.5°E which put it about 280 miles east of Tacloban and about 500 miles east-southeast of Manila, Philippines.  Mekkhala was moving toward the west-southwest at 11 m.p.h.  The maximum sustained wind speed was 75 m.p.h. and there were wind gusts to 90 m.p.h.  The minimum surface pressure was 974 mb.

The speed of the upper level east-southeasterly winds blowing over the top of Mekkhala weakened on Friday and the vertical shear affecting the circulation decreased.  The combination of less vertical wind shear and warm Sea Surface Temperatures allowed convection to develop all around the core of the circulation.  Strong thunderstorms near the center of Mekkhala created upper level divergence and the storm intensified rapidly into a typhoon.  Mekkhala remains in a favorable environment and further intensification is possible before it reaches the Philippines.  Once the center of circulation beings to move over the islands, interaction with land will weaken it.

A strengthening subtropical ridge has been steering Mekkhala a little south of due west and that motion is expected to continue in the short term.  The typhoon could reach the Philippines in about 12 hours.  Mekkhala could turn more toward the west-northwest as it crosses the Philippines and reaches the western end of the subtropical ridge.

Since Mekkhala has intensified into a typhoon the potential risks now include wind damage, and storm surge in addition to locally heavy rainfall, flooding and mudslides.

 

Tropical Storm Mekkhala Intensifies Slightly As It Moves Toward the Philippines

At 9:00 p.m. EST on Thursday the center of Tropical Storm Mekkhala was located at 11.6°N and longitude 131.1°E which put it about 540 miles east of Tacloban and about 710 miles east-southeast of Manila, Philippines.  Mekkhala was moving toward the west at 9 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.

East-southeasterly winds in the upper levels continue to cause moderate wind shear over the top of Mekkhala.  It has a well developed low level circulation, but most of the thunderstorm formation is still in the western half of the storm.  Although Mekkhala is over warm Sea Surface Temperatures, the wind shear is inhibiting intensification.  Further intensification is possible, but it will likely be limited.

A subtropical ridge north of Mekkhala is extending westward and the ridge should continue to steer it westward.  The projected path would bring Mekkhala near the central Philippines in 24 to 36 hours.  Potential risks include locally heavy rain, flooding and mudslides.

 

Tropical Depression 01W Forms East of Yap

The first tropical depression of 2015 over the Western North Pacific Ocean formed east of Yap on Tuesday.  At 7:00 p.m. EST on Tuesday the center of Tropical Depression 01W (TD01W) was located at latitude 10.1°N and longitude 139.9°E which put it about 130 miles east-northeast of Yap and about 1250 miles east-southeast of Manila, Philippines.  TD01W was moving toward the northwest at 13 m.p.h.  The maximum sustained wind speed was 35 m.p.h. and there were gusts to 45 m.p.h.  The minimum surface pressure was estimated to be 1000 mb.

A subtropical ridge is generating southeasterly winds over the top of TD01W and producing moderate wind shear.  The wind shear is causing much of the thunderstorm activity to be located in the northwestern part of the circulation around TD01W.  The lack of thunderstorms in the southern portion of the circulation is limiting the intensification of the tropical depression.  TD01W is over Sea Surface Temperatures that are around 30°C and so the potential for intensification exists if the speed of the upper level winds diminish.

The subtropical ridge is expected to continue to steer the tropical depression in a general west or west-northwesterly direction during the next few days.  This projected path could bring the tropical cyclone near the Philippines later this week.

 

Convection Redevelops in Remnants of Jangmi

Upper level wind shear decreased over the remnants of Jangmi on Thursday and thunderstorms redeveloped on the western side of the circulation.  At 11:00 p.m. EST on Thursday the center of circulation of the remnants of Jangmi was located at latitude 5.8°N and longitude 112.0°E which put it about 360 miles northeast of Kuching, Malaysia on the island of Borneo and about 600 miles east of Kuala Terengganu, Malaysia.  The center of circulation was moving just slightly south of due west at 8 m.p.h.  The maximum sustained wind speed was 35 m.p.h. with gusts to 45 m.p.h.  The minimum surface pressure was 1007 mb.

The subtropical ridge that was pushing strong southeasterly winds in the upper levels over the top of the remnants of Jangmi weakened slightly on Thursday.  As the upper level winds slowed down, it allowed more thunderstorms to develop around the western half of the circulation.  The increase of convection also increased the vertical extent of the circulation and created the potential for Jangmi to redevelop as a tropical cyclone.  The circulation is over Sea Surface Temperatures near 28°C, which provide sufficient energy to support a tropical cyclone.

As the circulation has grown taller, it has been steered more toward the west.  That pushed the center of circulation north of the northern tip of Borneo and kept it over the South China Sea.  Guidance suggests that the remnants of Jangmi will continue to move in a generally westerly direction which would take it toward Malaysia.

 

Remnants of Jangmi Approaching Northern Borneo

Wind shear continues to prevent reintensification of former Tropical Storm Jangmi and the circulation consists primarily of shallow convection.  The system still possesses a well developed cyclonic circulation in the lower atmosphere that is clearly apparent on visible satellite imagery.  At 11:00 p.m. EST on Wednesday the center of the remnants of Jangmi were located at latitude 6.8°N and longitude 118.8°E which put it about 175 miles west-northwest of Jolo in the Philippines, about 140 miles east of Kudat, Malaysia and about 150 miles northeast of Sandakan, Malaysia.  The center was moving toward the west-southwest at 6 m.p.h.  The maximum sustained wind speed was 30 m.p.h. and there were gusts to 40 m.p.h.  The minimum surface pressure was 1007 mb.

A subtropical ridge to the north of Jangmi continues to generate southeasterly winds with speeds near 35 m.p.h. in the upper levels over the system.  The strong upper level winds are shearing the tops of thunderstorms which start to develop near the center and are preventing the redevelopment of Jangmi.  The center of circulation is over warm Sea Surface Temperatures and so convection continues to develop but the strong wind shear keeps it shallow.

Since circulation is comprised almost entirely of shallow convection it is being steered by the winds in the lower level of the atmosphere.  Those winds are likely to continue to carry the circulation in a generally west-southwesterly direction, which would bring it near the northern coast of Borneo in 18 to 24 hours.  It could produce locally heavy rainfall and some flooding may be possible where it makes landfall.

 

Jangmi Weakens over Sulu Sea

Increased vertical wind shear blew the tops off of thunderstorms and Tropical Storm Jangmi weakened to a tropical depression,  At 11:00 p.m. EST on Tuesday the center of Tropical Depression Jangmi was located at latitude 8.0°N and longitude 120.8°E which put it about 150 miles north of Jolo, Philippines and about 300 miles east-northeast of Kudat, Malaysia on the northern end of Borneo.  Jangmi was moving toward the west-southwest at 7 m.p.h.  The maximum sustained wind speed was 30 m.p.h. and there were gusts to 40 m.p.h.

A subtropical ridge north of Jangmi intensified southeasterly winds in the upper levels and increased the wind shear over the top of the tropical storm.  The stronger upper level winds blew away the upper portions of thunderstorms and the circulation contained mainly shallower convection during the most recent 12 hours.  Recent satellite images show the redevelopment of some thunderstorms southwest of the center of circulation, but some wind shear continues.  Jangmi is over Sea Surface Temperatures that are warm enough to support some intensification, but that will not happen if the wind shear continues.  If Jangmi continues to move southwestward, interaction with the island of Borneo could weaken the circulation and possibly cause it to dissipate entirely.  If the center passes just west of Borneo, then some intensification may be possible, unless the wind shear remains too strong.

Since the circulation of Jangmi consisted mainly of shallower convection, it was steered toward the southwest by northeasterly winds in the lower levels of the atmosphere.  Even though a few thunderstorms have redeveloped, most of the convection is still shallow and Jangmi is likely to continue to be steered in a generally west-southwesterly direction.  The projected track could bring Jangmi or its remnants near the northern end of Borneo in 24-48 hours.