This year Northeast Monsoon has been a season of “Fits and Starts. Long dry spells interspersed with bouts of rainfall event that are of short duration. Unfavourable tropical waves during the first fortnight of November did not help either. The heaviest rains during NEM season is normally during LPA / Depression / Cyclone. But the rainfall meter keeps ticking with Easterly waves that happens time to time. This season we have seen very less easterly wave activity as well.
It may be ironic an Easterly wave may bring the last organised rainfall event of 2025. Starting from today for a period of 48 hours Tamil Nadu may see sporadic rains from this Easterly wave. Places along the coast between Pondy and Delta may initially benefit from these rains. As moisture pushes in places slightly to the west of this coastal stretch may also see rains. But with no other rainfall enhancing support in place the entire event may remain weak overall.
South TN though may see moderate to slightly heavy rains closer to the Ghats. Tirunelveli Ghats may see heavy rains from later tonight with occasional spells of very heavy rains. Coastal areas to the north of Pondy including Chennai may see light to moderate rains for the next 24 hours or so. Overall it may help keeping the soil moisture level up for a few days.
Looking at overall dynamics though it is fairly safe to assume from now on Northeast Monsoon through tropical forcing may not bring much rains. With ITCZ deepening to the South of Equator tropical wave transit over Indian Ocean may favour South Indian Ocean from now on. Rainfall events for Peninsular India may need to depend on interaction between tropical and sub tropical factors.
Parts of Middle east and adjoining areas may see very heavy rains from a fresh MJO pulse interacting with the westerly trough. These interactions happen in a very small window and would be tough to pick well in advance. At time even in short term windows these interactions develop very quickly. One such event in 2021 dumped very heavy rains over Chennai catching everyone off guard. If either of the factor, tropical or sub tropical, gets delayed the interaction may not happen at all leading to no / less rains.
But overall rainfall events from pure tropical forcing is likely to wind down from now on. Until middle of January there is always a chance for tropical / sub tropical interaction, particularly during a La Nina year. It remains to be seen if any such events happen during the remaining period of NEM 2025. It is essential to point out statistically Northeast Monsoon Season ends on 31st December. The dynamics may persist into January depending on atmospheric conditions.