As we get to the last days of the year anticipation for change starts becoming visible. The common people look forward to a fresh start with the new year. The weather bloggers though start showing signs of anxiety. Withdrawal symptoms as withdrawal of Northeast Monsoon season starts becoming imminent. More often than not it is North TN and South AP that sees the first sign of Monsoon withdrawal. As we get to the second half of December rainfall events are linked more and more to disturbances.
NEM 2024 has pretty much been one of those years that has been benevolent across Tamil Nadu. Only for the 3rd time in the last 10 years every district is either normal or above normal during NEM. As of yesterday only two districts are in the negative though within the normal band according to IMD protocol. Those two districts are Thoothukudi and Nilgiris. While Nilgiris has had a very good rainfall year Thoothukudi is the only district yet to reach its annual rainfall. All the other districts in TN & PDC have reached their annual quota of rainfall.
But all good things need to come to an end. Looking at weather forecasts, both operational and sub seasonal, there are indications North TN could see monsoon withdraw soon. It may sound ironic to say this when rains are likely for the next few days over North TN. Rains that may be due to the remnant circulation moving across the state as a Trough of Low. But looking a little further down shows why North TN can get ready for monsoon withdrawal.
Operational models are converging about the arrival of seasonal high pressure zone over Central India and Northern parts of Peninsular India. This would mean North TN and South AP are likely to come under the influence of drier continental winds. Once moist easterlies are replaced by drier continental winds rainfall prospects drastically reduce. Yes there could be rains when the dynamics become favouble due to a disturbance. But overall we can look forward to winter conditions gradually establishing.
But South TN and parts of Delta may need to wait before we can talk of Monsoon withdrawal there. A possible LPA during the first week of January could bring rains to South TN and Delta coast. As far as KTCC districts including Chennai we can gradually see rains wind down after the next few days. Looking at sub seasonal charts there is firm indication the ITCZ has been moving further south over South Indian Ocean. This could mean less favourable conditions for Bay of Bengal and Arabian Sea for disturbances to influence northern parts of the state. Sri Lanka and South TN could benefit from circulations over Equatorial waters during the 1st fortnight of January.
Ensembles also indicate most places in TN to receive light to moderate rains for the next week or so. The next few days possibly the last window for places like Chennai to get some rains before winter sets in.