Under the influence of an Upper Air Cyclonic Circulation that is now off the Andaman Islands a Low Pressure in Bay of Bengal is expected to form today. As models currently indicate this is expected to move in a W/NW direction over the next couple of days.
Current Situation & Model Divergence As things stand there continues to be some divergence in the model runs beyond Sunday, 29th November 2015. GFS continues to expect a second circulation to become the dominant circulation after 29th November. Both the models expect the Low Pressure in Bay of Bengal to move in a predominantly West direction towards Sri Lanka initially. The divergence happens at a point where the Low Pressure is at SE of Sri Lanka roughly at 6.5N – 7N latitude, a similar position where the Pre Diwali Depression was present. At this point GFS expects another circulation closer to Andaman to take over the reigns while ECMWF expects the Low Pressure Area to intensify and under the influence of a ridge over Myanmar take a NW turn towards the Indian Coast.
Shape of Things to Come (Valid till 29th Nov. 2015): As things stand considering the need to possibly interpret the evolving things fairly with the need to provide advance warning if need be without creating unnecessary panic we are putting our understanding until 29th November. We will continue to monitor the situation closely and update as soon as we see things change for the good.
From today till 29th we could see the coastal areas of Tamil Nadu to get some isolated spells of rains with the rainfall intensity increasing in the delta districts from tomorrow. As the Low Pressure comes closer to Sri Lanka the rainfall will become more widespread over Coastal TN with one or two places getting heavy rains. As things stand today and tomorrow Chennai could see isolated rains with Sunday possibly seeing one or two heavy spells.