Over the last 24 hours or so most parts of Coastal Tamil Nadu between Delta dts and Chennai received moderate to heavy rains under the influence of an interaction between Mid Latitude Westerly Trough and a trough of Easterlies over Southwest Bay of Bengal. As is the case more often than not when an interaction between Easterlies and Westerlies happen the impact zone was completely different from the area estimated by weather models. While most models indicated Chennai and surrounding KTCC districts to record extreme rains, with GFS expecting well in excess of 20 cms for the 24 hours ending today morning, to the contrary the heaviest rains happened between Pondy and Delta. The IMD observatory at Nagapattinam has recorded 17 cms up to 5:30 AM while the observatory at neighbouring Karaikal recorded 12 cms Except for Ennore / Kathivakkam zone most areas of Chennai and suburbs recorded around 4 to 5 cms of rains until today morning.
Today also the zone between Pondicherry and Nagapattinam may come under moderate to heavy rains in many places under the influence of the trough of Easterlies over SW Bay of Bengal off the coast of Sri Lanka. As the mid latitude Westerly trough moves away from the Indian sub continent the rains will gradually get influenced primarily by the Easterlies. This would mean it will stick to lower latitudes as the reason for the convection being pulled up North, Westerly trough, becomes less influential.
Additionally the anti cyclone over lower tropospheric levels is expected to gradually descend back into Peninsular India bringing about a reduction in rains and subsequently a cessation in rains over places like Chennai. Weather models indicate drier winds from North is expected to slowly move into South AP and adjoining areas of North TN gradually from tonight / early tomorrow morning which will lead to a cessation of rains over KTCC dts. As the drier winds descend further down places over North TN, Central TN also is expected to see a reduction in rains from Tuesday night / Wednesday morning. South TN may come under rains from tomorrow till Thursday or Friday before the trough of Easterlies fade away bringing about a cessation in rains for most parts of the state before Pongal festivities.
South TN though may keep a watch on possibly very heavy rains around the Tirunelveli Ghats during this period with the plains also likely to see moderate to heavy rains. As drier winds from North envelope rest of the state one or two places in this region may come under dry / moist air convergence bringing about a burst of heavy rains. The stretch between Thisaiyanvilai and Thoothukudi may be vulnerable to this type of sudden burst of rains. Tirunelveli Ghats around the Manjolai range may once again see a day or two of very heavy rains on Tuesday and Wednesday.
Chennai and suburbs may see on and off light to moderate rains during the early part of the day with heavy spells at times, though it may not last a long time, gradually the rains are expected to ease from later in the evening.