Northeast Monsoon 2023 – A tale of two monsoons

Weather Update
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Janus. As the god of transitions and dualities, Janus is portrayed with two faces—one facing the past, and one facing the future. In a way Northeast Monsoon 2023 also is a tale of two monsoons, one that shattered records in the districts of Thoothukudi and Tirunelveli and the other showing how extreme rainfall may be the future.

Northeast Monsoon 2023 will never be forgotten for the devastating rains parts of South Tamil Nadu faced during the middle of December. Many places in Tirunelveli and Thoothukudi recorded unprecedented rains and flood levels that has not been witnessed by the past couple of generations. Similarly it will be also be remembered for the extreme rains Chennai and suburbs faced as Cyclone Michaung slowed down near the coast of Chennai dumping a lot of rains in the process. We have seen in the past extreme rains happen in one or two places but both these episodes witnessed widespread extreme rainfall over a larger area rather than just one or two places. For example on 4th and 5th December 52 and 39 places recorded Very Heavy rains in the state when Cyclone Michaung came close. Similarly on 18th December a total of 35 stations in the TNSDMA network recorded extremely heavy rains indicating the widespread of the extreme rainfall event in South TN.

If one looks a little deeper we can see how Northeast Monsoon seasonal performance is skewed by the excess performance in a few districts over the extreme South and North Tamil Nadu along with a couple of them closer to the Ghats like Coimbatore, Teni etc. Kanyakumari and Tirunelveli have recorded twice the normal seasonal rainfall. The seasonal performance for more than 1/3rd of the districts is at 80% or worse in comparison to Seasonal Average. 10districts namely Kallakurichi, Krishnagiri, Tirupattur, Trichy, Perambalur, Dharmapuri, Ariyalur, Karur, Thanjavur and Tiruvannamalai have recieved less than 2/3rd of the normal seasonal rainfall as of 25th December. Not only parts of Tamil Nadu but large parts of Peninsular India has also see a poor post monsoon season particularly over parts of Rayalaseema in AP and adjoining interior districts of Karnataka.

The season was not only punctuated by long periods of subdued activity but the two extreme rainfall episodes pretty much pushed the seasonal average to 5% above normal as of 25th December 2023. Ironically four districts, Ariyalur, Krishnaigiri, Perambalur and Vellore saw a highest 24 hour rainfall during the season not even touch 7 cms during the entire season. Similar story is seen if one runs the Wet / Dry streak based on any station in the district recording / not recording 2.5 mm or more rains. While Kanyakumari saw 26 consecutive days when at least one station in the district recorded 2.5 mm or more Tirupathur on the other hand saw 19 consecutive days when no station in the district recorded 2.5 mm or more.

On the weather front convection continues to stay along the Equatorial Waters which will mean most parts of the state will remain dry except for some coastal places and parts of South TN where light to moderate rains may continue. As and when things evolve further updates would be provided if there is going to be a spell of significant rains over Tamil Nadu in the days to come.