Monsoons over the Indian Sub Continent, both Southwest Monsoon and Northeast Monsoon, not only go through intraseasonal oscillations but also go through long term decadal oscillation with positive and negative phases during these periods. While the human documented observations is just a couple of centuries old so any inferences based on very small data compared to the actual earth’s history is bound to be skewed many times it is fair to say both intra seasonal and long term oscillations in Monsoons is a phenomenon that continues to be studied and understood among weather reseachers.
The past couple of years Southwest Monsoon has been fairly robust for the leeward areas of Tamil Nadu. In this post back in February 2020 we had posted about how the seasonal rainfall trends for Southwest Monsoon has increased by about 100 mm between early 1900s’ to 2010s’. If one were to look at the data for Tamil Nadu and Pondicherry subdivision since 1951 the trend does not seem to be as strong as for example Chennai though the good news is leeward Tamil Nadu may be currently looking at a positive phase for Southwest Monsoon after the relatively subdued phase between early 2000s’ and mid 2010s’.
Even if one were to look at the current year’s performance of Southwest Monsoon except for a few most districts are currently in a positive status as far as rainfall anomalies go. With the next week or so looking good for the state, particularly the leeward areas, we may be seeing another good year for the state and a few districts may reach their seasonal tally by the time Monsoon reaches half way point.
Coastal areas of Tamil Nadu are likely to see another day of thunderstorms due to lower level wind convergence created by the weak westerlies. The last couple of days have seen storms come under the influence of weak wind steering providing for intense spell of rains from near stationary storms, like the one over Madurai & surroundings yesterday, today also we may see similar conditions with localized conditions playing a role in one or two places coming under intense spell of rains during evening / night hours.
Places to the west of Chennai is likely to see thunderstorms once again and if there is an interaction between the remnant storms from the west and sea breeze moving inland we could potentially see one or two places around Chennai and suburbs come under fairly heavy spell during the evening hours.