Post Monsoon season from October to December also happens to be the 'winter cyclone' period for the Indian Seas. Frequency of cyclones over Bay of Bengal (BoB ) and Arabian Sea (AS) is more during the northeast monsoon season than the pre monsoon, from March to May. BoB is more active basin than the AS, both in terms of number and intensity. However, the cyclones are known for defying the norms and live up to the reputation of being 'delusive'.
There is an appreciable decrease in the frequency of storms from November to December. Most of the storms originate over the BoB between 5deg and 10deg North latitude. Those which originate over Southwest BoB move initially in a northwesterly direction and strike the South Coromandel coast or northeast coast of Sri Lanka. A few of these enter Arabian Sea but they generally do not intensify and dissipate over the ocean itself. Storms which originate over South Andaman Sea and Southeast BoB move west-northwestward. Later, few of these recurve to head for Myanmar and Bangladesh. These storms have a large history of weakening before making landfall. Majority of BoB storms strike Coastal Andhra Pradesh and Tamil Nadu. Storms in the Arabian Sea are very few in December and most of them are of Bay origin.
Bay of Bengal has hosted a cyclonic storm every year since 2016. Year 2016 also has the distinction of churning two storms in December, one of them (Vardah) being very severe and of long duration.
All these storms formed in Bay of Bengal, except Pawan which originated over Western Arabian Sea, far from the Indian coast and weakened before striking Somalia coast. Cyclone Ockhi developed over BoB and later entered Arabian Sea but weakened before striking Gujarat coast as depression. All the Bay of Bengal cyclones, except Vardah weakened over the sea before making landfall. Vardah emerged as a low pressure area in the proximity of Malay Peninsula and intensified to a very severe cyclonic storm over south-central BoB. The tropical storm crossed Tamil Nadu coast, close to Chennai on 12Dec 2016 and weakened rapidly. Moving westward across South Peninsula, remnant of the storm entered Arabian Sea and intensified again to a deep depression, heading for Somalia. Cyclone Vardah prompted one of the largest evacuation of 16,000 people from the coastline of Tamil Nadu.
Currently, there is a cyclonic circulation over Malay Peninsula and Gulf of Thailand, extending up to upper levels. This is likely to enter South Andaman Sea and later become a well marked low pressure area over Southeast BoB, on 04th Dec2022. Intensifying further to a depression, the weather system is expected to move over south-central BoB on 05th Dec, late in the evening /night. Favourable oceanic conditions may trigger further sharpening. Ongoing activity of the easterly waves, overlayed on the depression field, stand a fair amount of chance of development of tropical storm over southwest BoB, off Tamil Nadu and Sri Lanka coast. Meteorological developments need to be kept under observation for another 36hr.
This will be the 2nd cyclone of northeast monsoon season, after Sitrang in late October, which struck Bangladesh. State of Tamil Nadu need to go on alert and the preparatory time be gainfully utilised to meet the challenge of stormy conditions between 06th and 08th Dec. Weather system is expected to move across South Peninsula, weaken and re emerge in the Arabian Sea.
