Tag Archives: Le Reunion

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.