Over many centuries the eastern coast line of the Indian Sub Continent has been shaped through an interaction of floods, sea and cyclones. There are a few areas which show a pronounced concave shape while a couple of them show a convex shape in the coastline. If one were to plot the strongest cyclone landfalls there would be a high correlation between the landfall points of these cyclones and the areas that sport concave coastline like Machilipatnam, Kavali, to some extent even Chilka lake in Odisha and the coastline between Cuddalore and Pondicherry. While there are some areas which show convex coastline feature nowhere it is more pronounced than the Chennai coastline with a near parabolic shape to the coastline. The convex coastline is an indication of lesser probability of cyclones making landfall based on past probability. In a way this also could provide a guideline on how coastal urbanization should take shape.
The convex coastline of Chennai though does come with a set of peculiar features. During the late May / June summers being possibly the eastern most land area over North TN and adjoining South AP Chennai has to bear the brunt of the heat from Rayalaseema. Similarly it also means practically very little thunderstorms during summer months on account of the Easterly influence well into mid May while interior areas benefit from the sneaking in Westerlies triggering wind instability influenced thunderstorms. Not only thunderstorms mostly skip Chennai during summer, the interior thunderstorms start moving into the coastline around Chennai only when Southwest Monsoon strengthens sufficiently enough to push the storms from the West. This often means June is the weakest month for rains during Southwest Monsoon for Chennai and surrounding areas.
Occasionally though Chennai gets a bonus spell of rains during June like the recent one which brought about the second highest 24 hour rainfall for Chennai AP during the month of June. This spell of rains was brought about by a developing circulation in South bay which eventually became a monsoon low reviving the monsoon dynamics after the subdued start. While earlier this week monsoon was active over the west coast from Friday there was a marked decrease gradually in the strength and simultaneously an uptick in the thunderstorm activity over the leeward areas of Peninsular East Coast. On Friday evening many parts of Cuddalore district recorded moderate to heavy spell of rains and a few suburbs of Chennai also witnessed good rains while last evening Pondicherry and surrounding witnessed good rains.
If one goes back a couple of weeks on 18th June Chennai and suburbs witnessed early morning drizzle / light rains which kickstarted the spell of rains which resulted in the heaviest downpour during June in more than a couple of decades. Similarly the current circulation in South Bay has started to deepen and move in a NW direction getting closer to the coast. This is likely to provide convergence over the Peninsular East coast between Nellore and Pondicherry providing a window of about 48 hours or so when most places in this stretch can catch atleast one or two good spell of rains. Just like 18th June Chennai and suburbs could see once again cloudy skies / light rains during the morning hours before evening thunderstorms return back over the interiors and late night thunderstorms over the coastal places.
A word of caution though while the overall pattern seems similar the rainfall quantum cannot be the same though there is a very high chance for the overall precipitation between today and Wednesday to touch about 10 cms for a few suburb of Chennai.