The trough line, along coastal Andhra Pradesh, which practically skirted Visakhapatnam and resulted in a heat wave in Visakhapatnam on Sunday, shifted westwards into the land on Monday. While Srikakulam and Vizianagaram and interior areas of Visakhaptnam district received rain, Visakhapatnam city got the ‘fringe benefit’ of drop in temperature on Monday due to the presence of clouds all along the trough line, says a retired Director of the India Meteorological Department (IMD) P.V. Rama Rao.
Trough line is a line joining areas of low pressure. Stations located on the trough line experience calm or variable light winds and people are subjected to oppressive hot weather and in inland stations in addition they experience light to moderate winds. Depending upon changes in pressure and wind field the trough line shifts westwards or eastwards from its position.
“When the trough line passes across coastal AP, stations located on the left of the trough line experience hot dry winds and those located to the right experience relatively cool weather. However, when the trough line passes over or lies along and off the coast, the flow of moist winds from the Bay of Bengal is arrested and in its place hot winds from central parts of India may extend over Andhra coast. This was what happened on Sunday (April 30) with the trough line passing over Visakhapatnam coast before shifting inwards, resulting in temperature soaring to 38 degree Celsius in the city and 41 at the Airport, which were 5 degree above normal,” says Dr. Rama Rao The pressure on either side of the trough line will be high, while it would be the lowest along the central point. The places, which do not have a coast experience hot weather on either side of the trough line as they do not get moisture feed from the sea.
Heat wave conditions for the first time in this season were experienced at isolated places in Prakasam, Nellore and Chittoor districts of AP and at isolated places in Mahbubnagar, Hyderabad and Adilabad districts in Telangana, about a month ahead of the normal dates, on April 17.
“The present weather trends indicate maximum temperatures would be more than normal in May and in the first half of June and heat wave conditions could be experienced for 25 days during the period instead of normal 10 to 15 days,” says Dr. Rama Rao.
