The Northeast monsoon has set in over Tamil Nadu and other southern states after the Southwest monsoon fully withdrew, according to the Regional Meteorological Centre (RMC), Chennai. The weather office said heavy rain is likely in 27 districts of Tamil Nadu on Thursday, with an Orange Alert issued for six districts for very heavy rain.
RMC Chennai Director V.R. Durai said the Southwest monsoon rainfall over Tamil Nadu this year was 21% below normal. He noted that similar low rainfall was recorded in 2002, 2012 and 2016.
For the Northeast monsoon season, the department expects above-normal rainfall over southern and delta districts, below-normal rainfall over northern districts, and near-normal rainfall over coastal districts. The assessment is based on factors including higher land temperatures and frequent changes in sea currents.
The RMC also pointed to El Niño conditions, with temperatures around 3°C above normal, while noting that Tamil Nadu has historically recorded higher Northeast monsoon rainfall during El Niño years. However, the formation of low-pressure systems over the Bay of Bengal may reduce, and a low-pressure area is expected only about a week after the monsoon onset.
In its latest bulletin, the RMC said a low-pressure trough extends from the south Tamil Nadu coast to beyond the Odisha coast across the northwest Bay of Bengal. Very heavy rain with thunder, lightning and gusty winds is likely in Nilgiris, Coimbatore, Theni, Dindigul, Tenkasi and Madurai, for which an Orange Alert has been issued. Heavy rain with thunder and gusty winds is also possible in several other districts and Puducherry, while Chennai and suburbs may see partly cloudy skies with moderate rain in a few places.
