With more than half the NEM season gone it is that period when each potential LPA gives a sense of excitement, expectation and worry. Excitement for the pluviophiles who look forward to heavy rains. Expectations from people belonging to places that have seen less rains in the season so far. Worry from people who have seen past events bring unpleasant experiences and losses. It is also time for weather bloggers to track every signal coming out from the developing LPA.
NEM 2024 has been a yo yo season so far despite showing positive anomaly. The interior areas of Tamil Nadu got some good rains during transition season. Rains over North Coastal TN have been patchy with Chengalpattu, Kanchipuram and Villupuram districts in deficit. Delta coast struggled during the first half of the season with no major spells. The last one week turned the tables bringing districts like Nagapattinam, Mayiladuthurai to the positive. Vedaranyam which recorded 21 cms during October has recorded 76 cms during November. Of this 76 cms the last 7 days has brought in 64 cms. Similarly the last 7 days has brought in 70 cms for Kodiyakarai.
Yesterday we saw parts of Ramanathapuram district come under extreme cloud burst rains. While the TNSDMA Rain gauge in Rameswaram recorded 36 cms in 3 hours the IMD Observatory at Pamban recorded 19 cms. The cyclonic circulation over Comorin Sea area played a key role in enhancing the wind convergence triggering this extreme rains. The change in fortunes for Delta and the extreme rains over Ramanathapuram district are interlinked. Wind convergence that favoured Delta initially brought in the rains yesterday over Ramanathapuram. Today with further shift to the south parts of South Coastal TN may benefit from widespread rains.
In the meanwhile all eyes will be on the cyclonic circulation over the South Andaman Sea. This circulation is likely to become an LPA in the next 48 hours. What is an NEM without twists and turns. As usual global models struggle with Bay dynamics. Two patterns picked up by models once the LPA forms to the East of Sri Lanka. The first scenario takes the circulation across Sri Lanka, Comorin Sea, South TN and into Arabian Sea. The second scenario takes the circulation on a more NW path skipping Sri Lanka and bringing it as a Depression / Cyclone off the coast of TN.
A couple of years back immediately after Cyclone Mandous made landfall over Mahabalipuram models picked up another extreme rainfall event over Coastal TN. The event eventually happened over the Sea well east of TN Coast. A small change in how the interaction between lower level Easterlies and mid level Westerlies changed the dynamics. Similarly a small change in how the LPA moves and intensifies could change the impact zone and rainfall potential over Tamil Nadu.
Considering the two contrasting scenarios which could either favour South TN or North TN it may be prudent to wait. Waiting patiently for the next 48 hours while the circulation evolves into an LPA may be the best choice. There is a good chance for a widespread rainfall event over Tamil Nadu next week. But as mentioned in the opening lines with contrasting emotions likely it is important to wait. Important to wait for nature to evolve and give us clear signals.