To a common man the arrival of the Tamizh month of Margazhi pretty much heralds winter. Not only do they associate Margazhi with the arrival of winter conditions but cessation of rains too. But ask a weather enthusiast he would say during La Nina winter takes a back seat for Peninsular India. The reason for this is the persisting Easterlies and associated lower level moisture with it. This also leads to rainfall events happening over coastal areas of Tamil Nadu even as late as Pongal period.
But when the overall atmospheric conditions are suppressive we can see phases of winter conditions between rainfall events. Even during peak Northeast Monsoon period when a cyclone is about 250 kms East of the coastline temperatures could drop. This is due to the strengthening winds from the land. As we get to January the diurnal high pressure over interior areas of Peninsular India shows up. This gradually starts playing a more prominent role in modulating night time minimum temperatures.
Particularly when the Easterlies are weak this becomes more pronounced leading to reduction in temperatures over most parts of interior Tamil Nadu. Over the last couple of days interior areas of TN has started to see a gradual reduction in night time temperatures. Many places in the plains like Dharmapuri, Coimbatore, Salem, Madurai AP, Tiruthani and Vellore recorded sub 20°C temperatures yesterday. Karur Paramathi was the coldest place in the plains of Tamil Nadu with 14°C. Over the next few days until possibly Thursday this is likely to be the trend.
Interior areas of Tamil Nadu may see night time minimum temperatures stay below 20°C over most parts of the state. This is likely to be 2 to 4°C below normal until Thursday. Clear skies due to overall dry conditions will also play a role in reducing night time temperatures. Subsequently under the influence of a possible LPA in South Bay the Easterlies may revive. When the Easterlies revive not only would it bring back cloudy skies / rains leading to warmer nights. Coastal areas may be modulated by proximity to sea so the temperatures may not drop as much as interior areas.
Ensembles also indicate drier conditions to prevail for the next few days. Most places of TN is showing less probability of rains. On Probability of Rains we have added a chart today to help understand the ensemble rainfall table better. Ensembles primarily work on Butterfly effect where a small change in initial conditions could bring drastically different outputs further down the line. Ensembles allow us to be prepared for all possible scenarios.