CHENNAI: As people peered into the sky looking for signs of rain, tiny instruments anchored to a maximum depth of 3000m in Bay of Bengal (BoB) were perhaps the first to pick up signs of an impending cyclonic storm, 500m underwater, about a week ago. As the weather system began its journey towards the Tamil Nadu coast across the Bay of Bengal, ocean data buoys played a key role in tracking its path and intensity.Four buoys in the Bay of Bengal and one in the Arabian Sea deployed by citybased National Institute of Ocean Technology ( NIOT ) helped the IMD track the trajectory of Cyclone Gaja along its path.The buoys were the first known instruments to send out warnings about the fury the storm may unleash on the land.As the eye of the storm crossed BoB, the buoys measured a drastic drop in air pressure and rise in wind speed and sea surface temperatures. When the sensors installed in the buoys sensed the abnormal conditions at sea, they automatically switched from a normal mode of transmitting data every 30 minutes to a rapid mode of relaying. They were also the ones that detected signs of the system intensifying into a severe cyclonic storm. “The data from our buoys are a value addition to our friends in IMD as it indicates the path of the cyclone. We were only aiding them and this time too, the predictions were accurate,” said M A Atmanand, director, NIOT.The research lab has deployed a total of seven deep sea buoys and two coastal buoys along the Bay of Bengal. These instruments have previously helped track the path of cyclone Vardah in 2016, when scientists utilised the rapid mode of data transmission for the first time.NIOT ocean observation programme director R Venkatesan said one of the four buoys, along the route of Gaja, identified as BD11, which was closest to the storm measured the maximum wind speed at 50.92kmph, the lowest air pressure at 1002 hPa and the highest wave height of 5.1m.As Gaja weakened after landfall and moved towards the west on Friday evening, a buoy in the Arabian Sea detected it.“Buoys give us data on several parameters like pressure, wind direction and SST on other days as well. They are additional data that help us in our forecast daily,” said S Balachandran, DDG, IMD

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