Category Archives: Indian Ocean

Tropical Cyclone Bansi Moving Away from Mauritius

At 9:00 p.m. EST on Thursday the center of Tropical Cyclone Bansi was located at latitude 19.0°S and longitude 64.1°E which put it about 385 miles east-northeast of Port Louis, Mauritius.  Bansi was moving toward the east-southeast at 12 m.p.h.  The maximum sustained wind speed was 130 m.p.h. and it was estimated there were wind gusts to 160 m.p.h..  The minimum surface pressure was estimated to be 937 mb.

Bansi was in an environment of low vertical wind shear and warm Sea Surface Temperatures for much of Thursday and intensified slightly.  The speed of the upper level winds is increasing and the cloud pattern is showing signs of more wind shear.  A subtropical high pressure system is likely to move Bansi toward the southeast at a faster speed.  Bansi is likely to continue to move toward higher latitudes which will move it over colder water.  The speed of the upper level winds will also increase and so Bansi should weaken during the next few days.

 

Tropical Cyclone Bansi Maintaining Intensity Northeast of Mauritius

At 11:00 p.m. EST on Wednesday the center of Tropical Cyclone Bansi was located at latitude 17.6°S and longitude 60.3°E which put it about 270 miles northeast of Port Louis, Mauritius.  Bansi was moving toward the east-southeast at 8 m.p.h.  The maximum sustained wind was 105 m.p.h. and it was estimated there were wind gusts to 125 m.p.h.  The minimum surface pressure was estimated to be 954 mb.

An eyewall replacement cycle altered the structure of Tropical Cyclone Bansi.  It previously had a small eye which had a diameter of 10-15 miles.  The outer eyewall has not contracted significantly since the inner eye dissipated.  Thus, Bansi is now a tropical cyclone with a large circular eye with a diameter of about 60 miles.  The circulation around Bansi seems to have achieved a rough equilibrium  with its surrounding environment and the intensity did not change much on Wednesday.  Bansi remains over warm Sea Surface Temperatures and in an area of light upper level winds.  So, it is still possible that some intensification could occur in the short term.  When Bansi moves to a higher latitude it will encounter cooler water and more wind shear and start to weaken.

A subtropical ridge near Bansi is expected to start to exert a greater influence and start to accelerate it toward the southeast at a faster speed in about 24 hours.

 

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.

 

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.

 

Tropical Cyclone Nilofar Weakening Rapidly Over the Arabian Sea

Strong southwesterly winds in the upper troposphere are generating vertical wind shear over the top of Tropical Cyclone Nilofar.  The wind shear is blowing the upper part of Nilofar’s circulation northeast of the low level center of circulation and causing the tropical cyclone to weaken rapidly.  At 8:00 a.m. EDT on Thursday the center of Tropical Cyclone Nilofar was located at latitude 20.3°N and longitude 64.5°E which put it about 350 miles south-southwest of Karachi, Pakistan and about 550 miles west of Mumbai, India.  Nilofar was moving toward the northeast at 7 m.p.h.  The maximum sustained wind speed was 50 m.p.h. and there were wind gusts to 65 m.p.h.

An upper level trough to the northwest of Nilofar is pushing strong southwesterly winds over the top of it.  There is evidence on satellite imagery that the wind shear may be strong enough to detach the upper portion of Nilofar’s circulation and transport it northeast of the low level center.  When the upper portion of the circulation is sheared away and detached, it removes the warm core and eliminates the ability of the cyclone to pump out the mass which is converging on the low level center.  If the wind shear were to lessen, Nilofar might be able to re-establish the link between the circulation in the lower and upper levels.  However, the wind shear is not expected to diminish and so Nilofar is likely to continue to weaken.  It may no longer meet the criteria to be classified as a tropical cyclone in another 24-48 hours.

The lower level circulation of NIlofar is expected to continue toward the northeast in the short term.   If the lower level circulation becomes shallow enough, then the southwesterly winds in the upper levels could blow over the top of it.  If that happens, then the lower level circulation could drift in the northern Arabian Sea until it spins down.  Some of the moisture associated with the circulation of Nilofar could get transported into parts of eastern Pakistan and western India where it could enhance precipitation.

 

Tropical Cyclone Nilofar Intensifies Into the Equivalent of a Major Hurricane

Light winds in the upper troposphere allowed the circulation around Tropical Cyclone Nilofar to pump out sufficient mass to enable it to intensify into the equivalent of a Major Hurricane.  At 8:00 a.m. EDT on Tuesday the center of Nilofar was located at latitude 16.8°N and longitude 61.8°E which put it about 315 miles southeast of Masirah Island, about 650 miles south-southwest of Karachi, Pakistan and about 740 miles west of Mumbai, India.  Nilofar was moving toward the north at 11 m.p.h.  The maximum sustained wind speed was 135 m.p.h. and there were wind gusts estimated to be 160 m.p.h.

The environment around Nilofar is capable of supporting an intense tropical cyclone, which is what Nilofar has become.  The upper level winds are light, which has allowed upper level divergence to spread the air in all directions.  In addition, the upper level outflow from Nilofar has interacted with surrounding weather systems to create outflow channels to the northeast and to the southwest.  The favorable atmospheric environment combined with warm Sea Surface Temperatures, which are supplying plenty of energy to Nilofar, has produced a strong tropical cyclone.  Nilofar could intensify further, although it is at the intensity where eyewall replacement cycles could begin to cause fluctuations in intensity.

Nilofar is moving around the western end of a subtropical high pressure system which is steering it to the north.  An upper level trough in the westerly flow north of Nilofar will eventually turn it toward the northeast.  Nilofar could threaten parts of Pakistan and India by the end of the week.  However, the southwesterly winds in the upper level trough will also generate more wind shear and Nilofar could start to weaken rapidly when it moves toward the coast of South Asia.

 

The Winds in Tropical Cyclone Nilofar Reach Hurricane Intensity

Tropical Cyclone Nilofar (Tropical Cyclone 04A) intensified on Sunday and it is now the equivalent of a hurricane.  At 8:00 p.m. EDT on Sunday the center of Nilofar was located at latitude 14.8°N and longitude 62.8°E, which put it about 470 miles southeast of Masirah Island, about 750 miles south-southwest of Karachi, Pakistan and about 720 miles west-southwest of Mumbai, India.  Nilofar was moving toward the north-northwest 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.

Well developed upper level outflow was pumping out mass and Nilofar intensified steadily on Sunday.  The upper level outflow remains well developed and there appear to be outflow channels to the southwest and northeast.  So, further intensification is possible in the shorter term.  Nilofar is expected to move northward and eventually stronger westerly winds will increase the wind shear and start to weaken the tropical cyclone.

Nilofar has been moving slowly toward the northwest.  It is likely to continue moving northward during the next 24-48 hours.  When Nilofar gets farther north, southwesterly winds on the east side of an upper level trough will turn it more toward the northeast.  Nilofar could eventually make a landfall in Pakistan or India, but the stronger upper level winds will weaken the circulation before it reaches the coast.

 

Tropical Cyclone Forms Over the Arabian Sea

A banded structure developed within an area of thunderstorms over the Arabian Sea and it has been classified as a tropical cyclone.  At 8:00 p.m. EDT on Saturday the center of Tropical Cyclone 04A was located at latitude 14.1°N and longitude 63.0°E which put it about 515 miles south-southeast of Masirah Island.  Tropical Cyclone 04A was moving toward the north at 5 m.p.h.  The maximum sustained wind speed was 40 m.p.h. and there were gusts to 50 m.p.h.

The tropical cyclone had been moving toward the northeast, but it appears to be turning more to northwest in response to a strengthening ridge of high pressure.  It is expected to move toward the northwest during the next 36-48 hours.  As the tropical cyclone approaches Oman, an upper level trough is expected to turn it toward the northeast.  There is some spread in the model guidance about when and where the turn toward the northeast will occur.  Therefore there is greater than normal uncertainty about the track forecast at longer time periods.

Upper level divergence is pumping out mass toward the northeast and southwest of the circulation.  As a result the surface pressure should fall and the tropical cyclone is expected to intensify during the next 48-72 hours.  Winds could reach hurricane force as the tropical moves in the general direction of Oman.