Dhanushkodi Cyclone of 1964, Sri Lanka cyclone of 2000, Thane during 2011 all formed during 2nd fortnight of December. All of them have one other thing in common, these were La Nina years, which saw late season surge. Northeast Monsoon more often than not has seen late season surge during La Nina years. While there are no indications of a cyclone there are enough indications Monsoon will remain active. Currently the seasonal performance of TN & PDC stands at 465 mm as of yesterday. It appears NEM 2024 may end up among the Top 30 years looking at indications.
Over the past couple of days under the influence of the Well Marked Low widespread rains have happened over Tamil Nadu. Delta and surrounding coastal areas got good rains from Tuesday that continued yesterday too. North Coastal TN including Chennai and suburbs saw widespread heavy rains yesterday. Later in the evening as the WML moved further into Gulf of Mannar parts of South TN started to see widespread heavy rains. Places along the eastern slopes in Virudhunagar, Tenkasi and Tirunelveli districts recorded extremely heavy rains during the night.
The current rainfall event is likely to continue for the next 24 to 36 hours. But it is now essential to keep a tab on the next disturbance. A cyclonic circulation in an area of disturbance over Malay Peninsula is likely to move into South Bay. Over the next 24 to 48 hours this is likely to deepen into a Low Pressure Area. Weather models are in tight agreement this LPA is likely to become well marked. Gradually it will also move towards ENE of Sri Lanka by 16th morning. A few models are expecting the WML to further intensify into a depression. There is a chance it could become a Deep Depression as it is moves over more open waters of Bay. The last two disturbances moved much closer to Equator while this one may move in the open waters.
Irrespective of the intensity of the disturbance one needs to be wary of the magnitude of rains. North Indian Ocean basin continues to remain one of the warmest ocean bodies globally. Due to this rainfall events are getting enhanced when the disturbance comes closer to the coast. We have seen similar trend with pretty much every rainfall event this NEM season including the current one. Effectively what we are seeing is the actual rainfall event is bigger than model estimated rainfall quantum. This puts more pressure on disaster managers as quantum of rains challenge infrastructure.
There is increasing alignment among weather models for widespread heavy rains over Coastal Tamil Nadu between 16th and 18th. Chennai to Delta coast once again is likely to be the hotspot for heaviest rains. A likely interaction between upper level westerlies and lower level Easterlies should be watched out for. Due to this interaction there is a chance for extremely heavy rains over North Coastal TN. This could be picked up only through real time observations when the WML comes closer to the coast. All in all another La Nina year is seeing a Late Season surge during December.
As usual we end with the Key Take Aways for the next few days.
- The current WML over Gulf of Mannar is likely to drift westward towards Arabian sea and gradually weaken.
- South TN and adjoining interior areas will see widespread heavy rains continue for the next 24 hours or so. Subsequently the rains may reduce for a small break of one or two days.
- North TN may see a break in rains for the next couple of days.
- A fresh LPA is likely to form over Southeast Bay in the next 24 to 48 hours.
- It is likely to become well marked and possibly intensify into a depression by the time it reaches Coastal TN.
- There is a 50:50 chance it may intensify into a Deep Depression considering its genesis location.
- Widespread heavy rains is likely over Coastal Tamil Nadu between 16th to 18th December.
- The abnormally warm ocean temperatures once again could enhance the actual rainfall event. There is a high chance actual rainfall may be once again higher than model estimated range.
- Delta to Chennai may remain once again the hotspot for heaviest rains.
- There is likely to be an interaction of upper level westerlies and lower level easterlies during the upcoming LPA. This could potentially could trigger extremely heavy rainfall event over few places in North TN. This could be identified only through real time observation.
- NEM 2024 to remain active until end of next week. We need to wait and watch if there is likely to be anotherLPA during the last week around Christmas.
STAY ALERT, BE PREPARED, PANIC NOT