Tamil Nadu’s northeast monsoon is expected to deliver near-normal rainfall overall in 2026, but an El Nino event could produce sharply uneven weather, with repeated storm-driven rain along the coast and prolonged dry conditions in interior districts, according to the Agricultural Climate Research Centre of Tamil Nadu Agricultural University.
The centre’s district-level forecast covers the October-to-December northeast monsoon season. It estimates that Tamil Nadu will receive 468 mm of rainfall during the season, close to the long-term average of 464 mm. The forecast comes after the state received 254 mm of rain between June 1 and September 22, which is 13% below the long-term average of 292 mm for the period.
The centre said the expected near-normal northeast monsoon could partly offset the rainfall deficit recorded so far. Improved inflows into water bodies and a rise in groundwater levels are possible if the seasonal rainfall is received as forecast, the assessment said.
However, the state-wide average may conceal major district-level differences. The centre has warned that the prevailing El Nino conditions could affect the distribution of rainfall. Coastal districts may experience continuous rain associated with cyclonic systems, while interior districts could face extended dry spells. The forecast therefore points to a season in which the total rainfall received by the state may be close to normal, even as local water conditions vary widely.
The northeast monsoon is particularly important for Tamil Nadu’s water and agricultural systems. It contributes about 50% of the state’s annual rainfall, making the season a key period for replenishing reservoirs, ponds and other water bodies, as well as supporting groundwater recharge and irrigation.
The centre has advised farmers to store excess rainwater in farm ponds when heavy rainfall occurs so that it can be used for irrigation during dry periods. The forecast places Tamil Nadu’s average northeast monsoon rainfall in the range of 434 mm to 438 mm, according to the report.
Sathyamoorthy, head of the Agricultural Climate Research Centre, said the current assessment covers rainfall expected over the next three months. He said the northeast monsoon is likely to begin in the second week of October and may become fully established by the third week of the month.
Rain has already been reported in the Western Ghats area around Coimbatore, including the Coimbatore Courtallam and Siruvani dam regions, Sathyamoorthy said. The centre’s forecast will be relevant to local authorities and water managers because a coastal storm event and an interior dry spell would require different responses, even within the same overall monsoon season.
The immediate monitoring points are the onset of the northeast monsoon, the distribution of rainfall across coastal and interior districts, and the ability of farmers and local water systems to capture excess rain for use during subsequent dry periods.
