For the past few days most of Tamil Nadu has been seeing thunderstorms under the influence of the Upper Air Cyclonic Circulation that formed over South Bay and gradually moved west. While interior areas enjoyed very good spell of rains coastal areas did not benefit so much with places like Chennai remaining mostly a spectator except for one or two light to moderate spells here and there. All this could change today though with the development of a temporary vortex off the coast of Tamil Nadu. This temporary Upper Air Cyclonic Circulation is likely to create Northeast Monsoon like conditions over the coastal areas improving the rainfall possibility in the bargain.
While on a larger scale things are firming up for the withdrawal of Southwest Monsoon with both the circulations fading rapidly yesterday, the remnant of Cyclone Shaheen & the LPA over East India, the burst of thunderstorms over Peninsular India yesterday due to wind induced instabilities is another indication of the arrival of large scale seasonal change of winds. Though it is not time yet to talk about the onset of Northeast Monsoon yet one but weather bloggers now can look forward to the task of identifying the window of onset from deterministic model outputs.
Today’s satellite image in a way indicates Northeast Monsoon is not far away, one can be mistaken to look at it as a possible onset day considering the cloud mass over Coastal Tamil Nadu. Add to it the early morning rains which are typical of Northeast Monsoon days. But it is still Southwest Monsoon days because the current conditions is under the influence of the temporary vortex that has developed off the coast of Tamil Nadu creating pseudo NEM like conditions.
Additionally due to the nature of circulation one can expect the moisture to be recycled along the coastal areas of Tamil Nadu providing an opportunity for widespread rains over Coastal Tamil Nadu including Chennai. Today could be a good day for Chennai & suburbs to catch up a good spell of rains. With few places in line for heavy spell of rains along the coastal stretch between Chennai & Chidambaram, some of the southern suburbs could end up getting a very good spell of rains with some luck. Like yesterday due to wind instabilities few places along the Western Ghats may get heavy rains today too.