Tag Archives: 04B

Tropical Cyclone 04B Develops Over Northern Bay of Bengal

Tropical Cyclone 04B developed over the northern Bay of Bengal on Friday.  The circulation around an area of low pressure southeast of India strengthened on Friday and the Joint Typhoon Warning Center (JTWC) designated the system as Tropical Cyclone 04B.  Data from a scatterometer on a satellite indicated there were winds to 45 m.p.h. (75 km/h) in the western part of the circulation.  The Indian Meteorological Department was classifying the low pressure system as a depression and that was why it did not have a name.

At 4:00 p.m. EDT on Friday the center of Tropical Cyclone 04B was located at latitude 18.7°N and longitude 86.9°E which put it about 340 miles (550 km) southwest of Kolkata, India.  It was moving toward the north at 18 m.p.h. (29 km/h).  The maximum sustained wind speed was 45 m.p.h. (75 km/h) and there were wind gusts to 60 m.p.h. (95 km/h).  The minimum surface pressure was 994 mb.

Although there was a well defined low level center of circulation, the rest of the circulation of Tropical Cyclone 04B was not particularly well organized.  There were no strong thunderstorms near the center of circulation.  The stronger thunderstorms were occurring in a rainband 80 miles (130 km) northeast of the center of circulation.  Other bands revolving around the center consisted primarily of low clouds and showers.

Tropical Cyclone 04B is moving through an environment that is only marginally favorable for intensification.  It is moving over water where the Sea Surface Temperature is near 28°C.  So, there is enough energy in the upper ocean to support intensification, but that is about the only factor favorable for intensification.  Tropical Cyclone 04B is moving underneath the western end of an upper level ridge.  The ridge is producing southeasterly winds which are blowing across the top of the circulation.  Those winds are also causing moderate vertical wind shear and the shear is probably the reason why the band of thunderstorms is displaced northeast of the center of circulation.  It also appears that the western side of the circulation of Tropical Cyclone 04B is also pulling some drier air from over India into the system.  Tropical Cyclone 04B is unlikely to intensify due to the effects of moderate wind shear and drier air.

The upper level ridge is steering Tropical Cyclone 04B toward the north.  On its anticipated track Tropical Cyclone 04B could make landfall near Kolkata in 24 to 30 hours.  The primary risk is locally heavy rain which could cause flooding.  The rain is likely to reach northeastern India a few hours before the center of circulation makes landfall.

Tropical Cyclone Nada Develops Near Sri Lanka

Tropical Cyclone Nada developed over the Bay of Bengal near Sri Lanka.  At 10:00 a.m. EDT on Wednesday the center of Tropical Cyclone Nada was located at latitude 10.1°N and longitude 83.5°E which put it about 295 miles (475 km) east-southeast of Chennai, India.  Nada was moving toward the west-northwest at 14 m.p.h. (23 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 997 mb.

Microwave satellite imagery indicates that Tropical Cyclone Nada has a well organized, circular low level circulation.  However, most of the thunderstorms are occurring in bands southwest of the center and north of the center.  There are mostly low clouds and showers in the circular bands south and east of the center of circulation.  An upper level ridge over the northern Bay of Bengal is producing easterly winds which are causing moderate vertical wind shear.  The upper level easterly flow is inhibiting the development of thunderstorms east of the center of Tropical Cyclone Nada and those winds may be tilting the circulation toward the west.

The environment surround Tropical Cyclone Nada consists of factors that are favorable for intensification and factors that are unfavorable.  Tropical Cyclone Nada is moving over water where the Sea Surface Temperature is near 29°C.  So, there is sufficient energy in the upper ocean to support intensification.  However the easterly winds in the upper levels are restricting upper level divergence to the east of the tropical cyclone.  Moderate vertical wind shear will limit intensification unless the upper level winds weaken.  If the upper level winds do weaken, then Nada could strengthen given its well developed low level circulation.  Tropical Cyclone Nada only has about 24 to 30 hours before it reaches the coast of India and it will start to weaken once it moves over land.

A subtropical ridge north of Nada is steering the tropical cyclone toward the west-northwest and that general motion is expected to continue.  On its anticipated track the center of Tropical Cyclone Nada will pass north of Sri Lanka and it will approach the southeast coast of India in 24 to 30 hours.  Nada is likely to make a landfall south of Cheannai, India near Pondicherry.  Tropical Cyclone Nada is expected to continue to move to the west and it could emerge over the Arabian Sea in two or three days.

Tropical Cyclone Nada will bring gusty winds and locally heavy rain to northern Sri Lanka and southern India.  Locally heavy rain could cause flooding and mudslides in parts of northern Sri Lanka and Tamil Nadu, Kerala and Karnataka states in India.