India Meteorological Department (IMD) said cyclone ‘Sitrang’ over the North Bay of Bengal moved rapidly last night (Monday) and crossed the Bangladesh coast between Tinkona and Sandwip close to Barisal during 9.30 pm to 11.30 pm earlier than forecast. It had also failed to intensify as a severe cyclone apparently due proximity to land features and high wind shear.
High wind shear values (change in wind direction and speed with height) do not allow the storm structure to maintain strength beyond a point, and even gets compromised in the bargain. The weakening was also spectacular just as the speed with which it executed the landfall. It weakened into a deep depression by 2.30 am this (Tuesday) morning about 90 km North-East of Dhaka in Bangladesh; and 60 km North-North-West of Agartala; and 160 km South-West of Shillong (both in India). By 5.30 am, it weakened into a depression and shifted bearing to North-East Bangladesh, about 150 km North-East of Dhaka; 90 km North-North-East of Agartala; and 100 km South-South-West of Shillong.
To weaken further
It was expected to weaken into a well-marked low pressure area by mid-morning today (Tuesday). Light to moderate rainfall with isolated heavy to very heavy rainfall is likely at most places over Arunachal Pradesh, Assam, Meghalaya, Mizoram and Tripura today and isolated heavy rainfall over Arunachal Pradesh on Wednesday. Squally winds with speed reaching 40-50 km/hr and gusting to 60 km/hr are likely over the North Bay of Bengal and along and off the Bangladesh coast until noon and reduce thereafter. Squally winds with speed reaching 40-50 km/hr and gusting to 60 km/hr are likely over South Assam and adjoining Meghalaya, Mizoram and Tripura during this period. ‘Rough to very rough sea’ (wave heights of up to 20 ft) may prevail over the North Bay and along and off Bangladesh coast. Fishermen are advised not to venture into the North Bay till noon, the IMD said.
Watch for North-East monsoon
Cyclone ‘Sitrang’ having blown over, weathermen will shift their focus back to the Bay for signs of the North-East monsoon, which has been delayed by a few days. In an extended forecast for three days from October 30 to November 1, the IMD has predicted isolated to scattered light to moderate rainfall over Kerala, Tamil Nadu and Coastal Andhra Pradesh, as the winds get reorganised and the Bay waters return to calm. The north-easterly winds will get back organised without delay and set up a circulation off the Tamil Nadu coast in the next few days. This would be followed by a helpful easterly wave that carries a rain-head upfront, and approaching the Sri Lanka and South Tamil Nadu coast by the end of the month (in a week’s time).
US agency forecast
The US Climate Prediction Centre indicates the possibility of South Coastal Tamil Nadu and Kerala receiving moderate to heavy rainfall during the week ending November 1. The rains will get heavier during the next week (November 2 to 9) along the coasts of South Coastal Andhra Pradesh, Tamil Nadu and Kerala as well as the ghats of Karnataka and Tamil Nadu and with slightly lesser intensity over interior Tamil Nadu and Karnataka. A productive western disturbance will ambush into North-West India bringing rain and thundershowers, and importantly helpful winds to clear the air and lessen pollution.