
Northeast monsoon rains mostly slow down over Tamil Nadu in the last week of December. The northeast monsoon is normally seen making onset in the last week of October, later than the 20th during the last few years. This year, the onset commenced on 15th October 2024 and the season officially ended on 31st Dec 2024, recording above-normal seasonal rainfall. The winter monsoon rains are still continuing over the state, albeit with a pause in between. Both, the coast and interiors of the state measured moderate showers over the last weekend, 18th-19th Jan 2025.
The capital city Chennai has a modest normal of 16.2 mm rainfall in January. City observatories at Nungambakkam and Meenambakkam have recorded 46mm and 65.2mm of rainfall so far in January, which is much above the normal. The complete state, as such, has recorded 23.4mm rainfall against the normal of 10.3mm, an excess of 127%, between the 01st and 20th of January 2025.
The extended rains for the state are linked with the oceanic parameters of ENSO and MJO. La Nina conditions have been around for a little while now. The presence of La Nina is considered favourable for extended northeast monsoon rains. Also, the other oceanic parameter MJO (Madden-Julian Oscillation) has also been frequently sailing over the Indian Ocean. Currently, the MJO is propagating eastward across the Indian Ocean and is likely to remain in a favourable phase for the next about 10 days, that is, till the end of January.
With the prevailing conditions, the rains are expected to extend further for the remaining days of this month. Next two days, the 21st and 22nd of January, light rains are likely along the coastline. Showers will pause on the 23rd and 26th Jan 2025. Courtesy, another cyclonic circulation moving across Sri Lanka-Comorin- the Maldives are, with a trough extending northward, rainfall is likely to resume. Scattered rain and showers are likely Between 27th and 31st January. The southern half of the state will be at risk of receiving moderate rainfall, with isolated heavy rainfall in some places.
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