Here are the latest developments:
The storm, packing wind speeds of upto 100 kilometres per hour, is likely to cross the Andhra Pradesh coast near Machillipatnam shortly. (Live updates)
Heavy rains accompanied by strong gales are lashing Krishna, Visakhapatnam, West Godavari and some other parts of coastal Andhra Pradesh since early Friday. Authorities have closed the educational institutions, IANS said.
The IMD's bulletin early Friday said Helen moved slightly west-northwestwards in Bay of Bengal and lay centred at about 120 km east of Machillipatnam, 250 km east-northeast of Ongole and 200 km south-southwest of Vishakhapatnam.
The Met department has warned of a storm surge of about 1 to 1.5m height that could inundate the low-lying areas of West and East Godavari, Krishna, Guntur and the adjoining areas of Prakasam district at the time of landfall.
Around 25,000 people have been evacuated from low-lying areas, reports Associated Press quoting an official. Fishermen, too, have been warned against venturing into the sea. Authorities have hoisted warning signals at all ports along the state's coast.
The cyclone is likely to affect the second one-day international cricket match between India and the West Indies, scheduled to be played at Visakhapatnam on November 24.
Teams from the National Disaster Response Force (NDRF) have already been moved to Nellore and Prakasam districts. The National Disaster Management Authority (NDMA) has also rushed six teams to the region.
A control room to monitor the situation has also been opened at the state secretariat in Hyderabad. The control room numbers are 040-23456005, 23451043.
The weather department has clarified that Helen's intensity would be "much less" than cyclone Phailin, which slammed into the Odisha coast on October 12, bringing in its wake torrential rains and wind speeds of over 200 kilometres per hour in the state and in north coastal Andhra Pradesh.
Andhra Pradesh has a nearly 1000-kilometre-long coastline and the nine districts there cyclone threats every year, especially between September and November.
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