As we get to the last week of December it is time to discuss the inevitable. When does Northeast Monsoon come to an end for this year? As we have mentioned often statistically the Northeast Monsoon season ends on 31st December. But many years the monsoon dynamics may continue into January. In some cases they may collapse even before the year ends. Currently the seasonal tally for NEM 2025 stands at -1%. After 7 consecutive good years Northeast Monsoon is likely to end in negative zone for the first time since 2018.
This year’s monsoon was expected to be good with potential to be exceptional. But one has to admit it has only flattered to deceive. Since 23rd October the daily rainfall for Tamil Nadu and Pondicherry has been near normal or above normal only on 13 days. This pretty much sums up the extremely poor year we have seen on a temporal scale. It is a normal year since it is within the -19% to 19% range of IMD. But one has to accept Northeast Monsoon 2025 has been a poor year for many districts. Only 13 out of the 40 districts in TN & PDC has seen a positive anomaly year. Chengalpattu at -34% has seen one of the worst NEMs in recent years.
Looking at overall atmospheric dynamics it is fair to say monsoon dynamics has strengthened over Southern Hemisphere. Most of the convection is now seen South of Equator across all the basins from Africa to Pacific. In terms of cyclogenesis probability weather models show very less chance not only over North Indian Ocean but also Pacific. With ITCZ now deepening south of Equator it is fair to expect tropical waves to favour Southern Hemisphere.
Overall we are entering a period of weak cyclonic activity for North Indian Ocean. January to March is traditionally the leanest period in terms of cyclones in Bay of Bengal. Of the overall Cyclones / Depressions formed in Bay of Bengal since 1891 only 3% have formed between January and March. The total number of cyclones / depressions between January to April is lesser than what happened during April or December the two weaker months during active cyclogenesis conditions.
Seasonal temperature and rainfall anomaly charts also indicate weak monsoon conditions to prevail for the rest of 2025. While weather models indicate a weak disturbance to evolve over Equatorial bay during the cusp of 2025 and 2026 we need to see how much impact it could make. Nevertheless it may bring some rainfall activity to Coastal TN between Delta and South TN. This is unlikely to be strong and could possibly be the last rainfall activity of Northeast Monsoon 2025 before IMD announces withdrawal.