CHENNAI: The Bay of Bengal is gearing up for another weather system even as the region recovers from two successive severe cyclonic storms, an unusual sequence that meteorologists say warrants close monitoring as the northeast monsoon enters its most active phase.
A low-pressure area is likely to form over the southeast Bay of Bengal around November 13 and intensify into a well-marked low-pressure area within the subsequent 24 hours, according to the India Meteorological Department (IMD). If it develops into a depression or a cyclone, it would add to an already eventful season marked by the formation of Severe Cyclonic Storm Murasu and Very Severe Cyclonic Storm Arnab.
Mahesh Palawat, vice president (meteorology) at Skymet Weather, told TNIE the close succession of systems was unusual, particularly because two cyclones had developed back-to-back.
“Two back-to-back cyclones are very rare. Now, another system is likely to form. It may intensify into a depression, but we have to wait. Different models are showing different tracks, with some indicating movement towards Andhra Pradesh and others towards Myanmar. The picture should become clearer over the next 48 hours,” he said.
Palawat said the system is not currently expected to intensify into a cyclone, although warmer-than-normal sea surface temperatures could favour further development. He added most models did not indicate a threat to north Tamil Nadu at present, with some suggesting that the system could recurve towards the northeast.
The emerging pattern has drawn attention to the frequency of cyclonic disturbances this year. Palawat said the North Indian Ocean typically experiences around three to four cyclones annually, including systems during both the southwest and northeast monsoon seasons.
“If this system intensifies into a cyclone, it would be the third. We still have two months of the northeast monsoon to go,” he said.
Meanwhile, in view of the recent deaths of nine fishermen, the Fisheries and Fishermen Welfare Department has directed all mechanised boats and motorised traditional fishing boats that ventured into the sea from Chennai Fishing Harbour to return to shore by November 12.
Heavy rain likely in south TN
Heavy rain is likely at isolated places in Ramanathapuram, Thoothukudi and Tirunelveli districts on Wednesday, with thunderstorms, lightning and gusty winds reaching 40-50 kmph at one or two places, the Regional Meteorological Centre (RMC) said.
Moderate rainfall is likely in parts of the Cauvery delta and southern districts, including Thanjavur, Tiruvarur, Mayiladuthurai, Nagapattinam, Pudukkottai, Sivaganga, Madurai, Virudhunagar, Theni, Tenkasi and Kanyakumari. Light rain is likely at isolated places in the remaining parts of Tamil Nadu and Puducherry.
Rain activity is expected to continue in parts of the delta and southern districts on November 12 before easing on November 13, when mainly dry weather is forecast over most of Tamil Nadu. Rain is likely to return to several coastal and northern districts, including Chennai, Tiruvallur and Chengalpattu, on November 14. The weather office has forecast heavy rain in parts of the Cauvery delta on November 15. Heavy rain is also likely in the Nilgiris and Coimbatore districts on November 16.
Method to identify large-scale monsoon system
Chennai: The researchers at the Indian Institute of Technology Madras and Gauhati University have developed a method to distinguish between short-lived local rainfall and the arrival of the large-scale monsoon system.
The study, published in the Journal of Climate of the American Meteorological Society, uses a climate-network approach to track how rainfall at different locations across India gradually connects to form a large, interconnected system. Instead of identifying monsoon onset based on the first rainfall at a location, the method considers when local rainfall becomes part of the largest interconnected cluster of rainfall events across the country.
The researchers analysed 84 years of rainfall data and found the average large-scale monsoon onset occurs around May 15 over Northeast India and June 9 over the Indian peninsula. The study explains how small rainfall clusters develop over Northeast India during April, partly due to thunderstorms.
As the season progresses, these clusters merge with rainfall activity over the Bay of Bengal to form a larger system. A similar process occurs over the peninsula, where rainfall activity over Kerala eventually connects with the larger monsoon system moving westwards from Northeast India.