Tropical Cyclone Roanu moved closer to the northern coast of the Bay of Bengal on Friday. At 5:00 p.m. EDT on Friday the center of Tropical Cyclone Roanu was located at latitude 20.3°N and longitude 87.8°W which put it about 200 miles (320 km) south of Kolkata, India and about 355 miles (575 km) west-southwest of Chittagong, Bangladesh. Roanu was moving toward the northeast at 11 m.p.h. (18 km/h). The maximum sustained wind speed was 65 m.p.h. (105 km/h) and there were wind gusts to 80 m.p.h. (130 km/h). The minimum surface pressure was 983 mb.
On Friday Tropical Cyclone Roanu went through another cycle in which most of the thunderstorms dissipated near the center of circulation and then convection redeveloped rapidly. Thunderstorm activity is increasing at the core of the circulation and those storms are driving well developed upper level outflow. Several well formed bands of thunderstorms are rotating around the center of circulation. Roanu is more organized and it is a little more intense than it was 24 hours ago.
Tropical Cyclone Roanu is in an environment that could support a little more intensification before it makes landfall on the north coast of the Bay of Bengal. It is over water where the Sea Surface Temperature is near 30.5°C. Roanu is under an upper level ridge which means the upper level winds are light and there is not much vertical winds shear. However, Roanu is getting closer to the north coast of the Bay of Bengal and it only has another 12 hours or so to intensify.
A ridge east of Roanu is steering the tropical cyclone toward the northeast and that general motion is expected to continue for the next several days. On its anticipated track Tropical Cyclone Roanu will be near the coast of Bangladesh in about 12 hours. Roanu is expected to continue moving toward the northeast after it makes landfall.
Although Tropical Cyclone Roanu could cause some minor wind damage, its main threats will be locally heavy rain and a moderate storm surge. Tropical Cyclone Roanu could produce locally heavy rainfall, especially if the thunderstorm activity continues to pulse diurnally. The heavy rain could produce significant fresh water flooding over parts of northeastern India, Bangladesh and Myanmar (Burma). In addition, the winds on the eastern side of Tropical Cyclone Roanu will be blowing toward the coast of Bangladesh and those winds will push water toward the coast. The north coast of the Bay of Bengal is particularly susceptible to storms surges and Roanu could bring a moderate storm surge to the coast of Bangladesh. The surge will be higher in the mouths of rivers and other locations where the shape of the coast funnels the water into specific locations.
Tropical Cyclone Roanu intensified on Thursday and it poses an increasing threat to the northern Bay of Bengal. At 11:00 p.m. EDT on Thursday the center of Tropical Cyclone Roanu was located at latitude 17.9°N and longitude 84.9°E which put it about 125 miles (200 km) east of Visakhapatman, India and about 580 miles (935 km) west-southwest of Chittagong, Bangladesh. Roanu was moving toward the north-northeast at 14 m.p.h. (23 km/h). The maximum sustained wind speed was 60 m.p.h. (95 km/h) and there were wind gusts to 70 m.p.h. (115 km/h). The minimum surface pressure was 986 mb.
Most of the thunderstorms in Tropical Cyclone Roanu weakened earlier today and at times it did not look much like a tropical cyclone on satellite imagery. However, a burst of thunderstorm activity near the center of Roanu has occurred in recent hours and an eyelike feature has appeared on conventional satellite imagery. The structure of the circulation improved as a result of the new burst of thunderstorms. The primary rainband now coils more tightly about three quarters of the way around the apparent center of circulation. The thunderstorms near the center of circulation are generating upper level divergence which is pumping out mass in all directions. Several additional bands of thunderstorms have developed over the eastern half of the circulation and Tropical Cyclone Roanu is stronger than it was 24 hours ago.
Tropical Cyclone Roanu is in an environment favorable for intensification. It is over water where the Sea Surface Temperature is near 31°C. Roanu has moved closer to the center of an upper level ridge and the upper levels are not as strong as they were yesterday. As a result the vertical wind shear is much less and the upper level ridge is actually helping to pump mass away from the center of Roanu. The center of the tropical cyclone is near the east coast of India, but the core is expected to remain over water on Friday. Roanu is likely to strengthen further and it could reach hurricane/typhoon intensity.
A ridge east of Roanu is steering the tropical cyclone toward the northeast and that general motion is expected to continue. On its anticipated track Roanu could be south of Kolkata, India in about 18 hours. Tropical Cyclone Roanu could be approaching Chittagong, Bangladesh in 24 to 36 hours.
Tropical Cyclone Roanu poses a significant threat to the northern Bay of Bengal. That area is vulnerable to storm surges. Since Roanu will approach from the southwest, the winds in its counterclockwise circulation will push water toward the north coast of the Bay of Bengal. In addition, a strengthening Tropical Cyclone Roanu will be capable of producing locally heavy rain which could cause inland flooding.
The structure of a low pressure system north of Sri Lanka changed on Wednesday and it was classified as Tropical Cyclone 01B (TC01B). At 11:00 p.m. EDT on Wednesday the center of Tropical Cyclone 01B was located at latitude 15.9°N and longitude 82.3°E which put it about 155 miles (250 km) south-southwest Visakhapatnam, India. TC01B was moving toward the northeast at 12 m.p.h. (19 km/h). The maximum sustained wind speed was 50 m.p.h. (80 km/h) and there were wind gusts to 65 m.p.h. (105 km/h). The minimum surface pressure was 989 mb.
A low pressure system developed near Sri Lanka several days ago. The low moved over the east coast of Sri Lanka, which slowed the organization of the circulation. A more well defined center of circulation began to organize after the low moved north of Sri Lanka. A primary rainband started to wrap around the western side of the low and several broken spiral bands formed on the eastern side. The circulation exhibited enough characteristics associated with tropical cyclones to be classified as Tropical Cyclone 01B.
The circulation of TC01B is still not particularly well organized. A primary rainband curls around the northern and western sides of the circulation. However, there are not many thunderstorms in the other parts of the tropical cyclone. An upper level ridge over the northern Bay of Bengal is generating easterly winds over the top of the tropical cyclone. Those winds are producing moderate vertical wind shear and are contributing to the fact that most thunderstorms are west of the center of circulation. The fact that the center of circulation is near the coast of India also means a portion of circulation is over land, where there is more friction and less moisture.
Tropical Cyclone 01B is expected to move into a more favorable environment during the next two days. It is over water where the Sea Surface Temperature is near 31°C. TC01B is expected to move closer to the center of the upper level ridge where the winds are not as strong. That would reduce the vertical wind shear, which would also be favorable for intensification. However, the proximity of the center to the east coast of India means that a portion of the circulation will remain over land, which will slow the rate of future intensification.
A ridge is east of TC01B is expected to steer the tropical cyclone toward the northeast during the next two to three days. On its anticipated track, TC01B could be approaching the coast of Bangladesh in 48 to 72 hours. TC01B caused heavy rain in parts of Sri Lanka and southeast India. It could produce more heavy rain in parts of northeast India, Bangladesh and Myanmar (Burma). TC01B could also generate a significant storm surge along the north coast of the Bay of Bengal as it nears the coast.