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Eyewall Replacement Cycle Weakens Tropical Cyclone Bansi

At 7:00 p.m. EST on Tuesday the center of Tropical Cyclone Bansi was located at latitude 17.4°S and longitude 58.2°E which put it about 200 miles north-northeast of Port Louis, Mauritius.  Bansi was moving toward the east-southeast at 3 m.p.h.  The maximum sustained wind speed was 130 m.p.h. and it was estimated there could be wind gusts to 160 m.p.h.  The estimated minimum surface pressure was 944 mb.

An outer rain band wrapped completely around the existing eyewall of Tropical Cyclone Bansi to create concentric eyewalls.  As the low level convergence became concentrated on the outer eyewall, the inner eyewall began to weaken.  This resulted in a reduction of the maximum sustained wind speed and a rise in the minimum surface pressure.  Satellite imagery indicates that most of the inner eyewall has dissipated, but some of it still remains.  The strongest winds are now occurring in the outer eyewall.  The eyewall replacement cycle also resulted in a larger circulation.  Bansi is still over warm Sea Surface Temperatures and the upper level winds are relatively weak.  So, some reintensification is possible during the next 24 hours, but it is always challenging to predict intensity changes after an eyewall replacement cycle.  As Bansi moves to higher latitudes, the Sea Surface Temperature will decrease and wind shear will increase.  So, Bansi is expected to weaken later this week.

Bansi remains in an area of weak steering winds.  As a result, it is moving slowly toward the east-southeast.  A subtropical ridge is expected to strengthen in about 24 hours and begin to steer Bansi southeastward at an increasing speed.  The projected track is expected to keep the core of Bansi northeast of Mauritius.

 

Bansi Now a Powerful Tropical Cyclone North of Mauritius

Tropical Cyclone Bansi continued to intensify rapidly on Monday and it is now the equivalent of a Category 4 hurricane on the Saffir-Simpson Scale.  At 4:00 p.m. EST on Monday the center of Tropical Cyclone Bansi was located at latitude 17.6°S and longitude 57.2°E which put it about 175 miles north of Port Louis, Mauritius and about 225 miles north-northeast of Saint Denis, La Réunion.  Bansi was moving toward the east-southeast at 4 m.p.h.  The maximum sustained wind speed was 150 m.p.h. and it was estimated that there could be wind gusts to 185 m.p.h.  The minimum surface pressure was estimated to be 926 mb.

Bansi has been in a nearly perfect environment for rapid intensification of a tropical cyclone.  The Sea Surface Temperature is near 30°C, which means there is plenty of energy in the upper ocean.  The upper level winds are light and that has allowed convection near the center of circulation to drive strong upper level divergence.  The upper level divergence has pumped out mass and the pressure has fallen rapidly.  The circulation around Bansi is very symmetrical and there is a well developed eye that is visible on satellite imagery.  The environment around Bansi is expected to remain favorable for intensification and it is possible that it could reach the equivalent of a Category 5 hurricane.  Eyewall replacement cycles are common in strong hurricanes and if they develop they can cause periodic fluctuations in intensity.  Eventually,when Bansi moves toward higher latitudes, wind shear will increase and it will begin to weaken.

As the upper level winds around Bansi have diminished, the steering currents have weakened.  Bansi is expected to move slowly in a generally east-southeasterly direction for the next 24 to 48 hours.  The projected path would take the center northeast of Mauritius.  Eventually, a subtropical ridge is expected to strengthen and accelerate Bansi toward the southeast.  If a sharper southeasterly turn occurs, that would bring the center of Bansi closer to Mauritius.

 

Tropical Cyclone Bansi Intensifying Rapidly North of La Reunion

A tropical cyclone has intensified rapidly north of La Réunion during the past 24 hours.  At 1:00 p.m. EST on Sunday the center of Tropical Cyclone Bansi was located at latitude 17.1°N and longitude 55.1°E which put it about 300 miles north of Saint Denis, La Réunion and about 250 miles northwest of Port Louis, Mauritius.  Bansi was moving toward the south-southeast at 5 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 estimated to be 974 mb.

The circulation around Bansi organized rapidly on Sunday and it exhibits a symmetrical shape with a well developed eye at its center.  The circulation is small, but it has well developed upper level outflow to pump out mass.  Bansi is over Sea Surface Temperatures that are warmer than 30°C which provide plenty of energy to intensify the circulation further.  Bansi could intensify rapidly for another 24 hours and become a very strong tropical cyclone as it passes near Mauritius.

Bansi is being steered to the south-southeast by a ridge of high pressure.  The ridge is expected to continue to steer Bansi in a general southeasterly direction, although there could be short-term jogs to the east-southeast or south-southeast.  The anticipated track could bring Bansi near Mauritius in 48-72 hours.

 

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.

 

 

Tropical Storm Jangmi Moving across the Sulu Sea

Tropical Storm Jangmi moved across Mindanao and the center passed near Cebu.  It has now moved back over the open waters of the Sulu Sea.  At 11:00 p.m. EST on Monday the center of Tropical Storm Jangmi was located at latitude 10.4°N and longitude 121.0°E which put it about 320 miles south of Manila, about 200 miles east-northeast of Puerto Princesa and about 1300 miles east-northeast of Singapore.  Jangmi was moving toward the west at 11 m.p.h.  The maximum sustained wind speed was 45 m.p.h. and there were gusts to 60 m.p.h.

Thunderstorms are beginning to redevelop near the center of circulation now that it has moved back over water.  The low level center appears to be relatively intact after its passage over some of the islands in the southern Philippines.  Easterly winds in the upper levels are generating some wind shear, but there is well developed upper level outflow on the northern side of Jangmi.  It will be moving over warm Sea Surface Temperatures and some intensification is possible as it moves westward.

Jangmi is being steered to the west by a subtropical ridge located to its north.  The general westward motion is expected to continue in the short term.  Eventually, northeasterly winds are expected to push Jangmi in a more west-southwesterly direction over the next few days.  The projected track is expected to take the center across Palawan near Puerto Princesa in about 24 hours.  The west-southwesterly motion is expected to continue and it could take Jangmi in the general direction of Malaysia.

Jangmi could bring some locally heavy rainfall to parts of Palawan and some flooding and landslides are possible.

 

Tropical Storm Jangmi Develops Near the Southern Philippines

A well developed center of circulation formed in an area of thunderstorms near the island of Mindanao and the system has been classified as Tropical Storm Jangmi.  At 10:00 p.m. EST on Sunday the center of Tropical Storm Jangmi was located at latitude 8.8°N and longitude 126.0°E, which put it near the city of Prosperidad on Mindanao.  The center of Jangmi was located about 200 miles east-southeast of Cebu, about 500 miles east of Puerto Princesa and about 1550 miles east-northeast of Singapore.  Jangmi was moving toward the west-northwest at 10 m.p.h.  The maximum sustained wind speed was 45 m.p.h. and there were gusts to 60 m.p.h.

The atmospheric environment around Jangmi is generally favorable for intensification.  Easterly winds in the upper levels are causing some wind shear, and there is more convection on the western side of the storm.  However, upper level divergence is very well developed on the northern side of the circulation and the circulation is pumping out mass.  The center of circulation was organizing rapidly as Jangmi neared Mindanao and there was some evidence of an eye forming.  The center has now moved over Mindanao and movement over land will disrupt the circulation in the short term and it should limit the potential for intensification during the next 24 hours.  Sea Surface Temperatures around the southern Philippines are warm and Jangmi could intensify when it moves west of Mindanao.  The tropical storm will encounter cooler and drier air after it moves west of the Philippines.

Jangmi is being steered in a general west to west-northwesterly direction by a subtropical ridge to it north.  It is expected to continue in that general direction during the next day or two.  When Jangmi moves west of the Philippines it will encounter stronger northeasterly winds in the lower levels of the atmosphere.  Those winds could push Jangmi more toward the west-southwest later this week.

The relatively slow movement of Jangmi could create the potential for locally heavy rainfall over portions of the southern Philippines.  In places where the heaviest rain falls, it could create the conditions to produce some flooding and landslides.

 

Tropical Cyclone Kate Intensfies Rapidly over Southeastern Indian Ocean

Favorable oceanic and atmospheric conditions allowed Tropical Cyclone Kate to intensify very rapidly on Friday.  The maximum sustained wind speed increased from 50 m.p.h. to 120 m.p.h. during a 24 hour period.  At 10:00 p.m. EST on Friday the center of Tropical Cyclone Kate was located at latitude 12.9°S and longitude 93.8°E which put it about 215 miles west-southwest of the Cocos Islands and about 2450 miles west of Darwin, Australia.  Kate was moving toward the southwest at 5 m.p.h., which was taking it away from the Cocos Islands.  The maximum sustained wind speed was 120 m.p.h. which made Kate the equivalent of a Category 3 hurricane on the Saffir-Simpson Scale and it was estimated that there were gusts to 150 m.p.h.

Although there were upper level winds blowing from the east, which created some wind shear over Kate, it was able to develop strong upper level outflow which produced rapid intensification.  Some satellite imagery shows that the wind shear is causing the strongest thunderstorms to be on the western side of the center of circulation.  Recent visible and infrared satellite imagery show evidence of an circular eye developing.  Some further intensification is possible during the next 24 hours as long as the upper level outflow is able to pump out sufficient mass.  Eventually, as Kate moves toward higher latitudes the wind shear will increase and the Sea Surface Temperatures will decrease.  The more hostile environment will weaken the tropical cyclone and the weakening could be almost as rapid as the intensification was.

Kate is expected to continue to be steered in a generally southwesterly direction in the short term by a subtropical ridge.  As it moves farther south, it will begin to be affected by westerly midlatitude flow and it will start to recurve more toward the south.  Kate passed over the Cocos Islands earlier this week as a tropical storm.  It is expected to dissipate over the Indian Ocean and not affect any other land areas as a tropical cyclone.

 

Hagupit a Tropical Storm for One More Day

Thunderstorms continue to develop intermittently near the center of Hagupit and it is producing enough deep convection to maintain its status as a tropical storm.  At 10:00 p.m. EST on Wednesday the center of Tropical Storm Hagupit was located at latitude 13.2°N and longitude 113.1°E which put it about 275 miles east-northeast of Cam Ranh, Vietnam and about 460 miles east-northeast of Ho Chi Minh City.  Hagupit was moving toward the west-southwest at 9 m.p.h.  The maximum sustained wind speed was 40 m.p.h.  and there were gusts to 50 m.p.h.

Although Hagupit is moving over warm Sea Surface Temperatures, the rest of the environmental factors are unfavorable for intensification.  Northeasterly winds over the South China Sea are transporting cooler and drier air, which is wrapping around the western and southern parts of Hagupit’s circulation.  There is also significant vertical wind shear, which is tilting the circulation.  The tight low level center of circulation is producing enough convergence to continue generating some new thunderstorms near the center, but the convection is becoming more intermittent.  Hagupit is likely to slowly weaken during the next 24 hours as a result of the mainly hostile environment around it.

The northeasterly winds are likely to push Hagupit toward the west-southwest or southwest during the next 24 hours.  The projected track would bring Hagupit to the coast of Vietnam near Cam Ranh in about 24 hours.  It is likely to have minimal impact when it makes landfall.  There could be a period of gustier winds and an increase in rainfall, but Hagupit could dissipate fairly quickly as it moves inland.