December is often when the Northeast monsoon season ends, particularly in Chennai. It isn’t the situation now. And we all know, last few years NEM has extended till January. As we are in La-Nina & weak negative IOD conditions, winter rains possibility also not ruled out for Tamilnadu.
We talked a few weeks ago about how the Atlantic and west Pacific oceans had delayed active seasons, which made it difficult for the Northeast monsoon to attains it’s peak during the initial phase of monsoon especially till November 20th, 2024. Still we have got 446mm.
By the end of November and the early December, TamilNadu threatened by the rain-bearing cyclone #FENGAL, which quickly followed the suppression of the Pacific and Atlantic ocean. This event had a significant impact on parts of the coastal and interiors parts of North Tamil Nadu.
The Bay of Bengal will continue to benefit from planetary waves over the next two weeks. Over the Maritime continent, Madden Julian Oscillation is anticipated to be observed stationery. As a result, west Pacific Ocean will be remain silent until December 25th, 2024. Hence, streamlined arrival of moisture-filled easterlies from the Pacific Ocean are likely for next two weeks.
Additionally, equatorial Rossby wave likely to bring the cross equatorial westerlies support to the North Indian Ocean. Along with the planetary wave support & sea surface temperature ITCZ position also favouring Northeast monsoon. Hence, Bay of Bengal is all set to host back to back systems between Dec 10th and 25th, 2024.
Sea surface temperature has started showing increasing trend again over TamilNadu & Srilanka coasts. The ridges’ favourable position and the feeble impact of the westerly trough may prevent the system from rising above Tamilnadu’s latitude. Therefore, between December 10 and December 25, 2024, coastal Tamil Nadu is expected to have consecutive rainfall episodes and another vigorous monsoon phase.
Soil saturation has significantly increased in comparison to the last three rainfall occurrences, and water resources levels are generally close to 70–80%. We must thus use greater caution over the next three weeks. Even a little amount of rain could have a significant impact on the Cuddalore, Pudhucherry, and Villupuram zones.
I’m repeating again “short time extreme rains possibility with Heavy to very heavy rains with isolated extremely heavy rain chances” there at Chennai, Thiruvallur, Kanchipuram, Chengalpet, Villupuram, Pudhucherry, Cuddalore, Mayiladuthurai, Karaikal, Nagapattinam, Thiruvarur and Thanjavur dts between Dec 10th and 25th, 2024.
Here, our Northeast monsoon impact map for November & December which has published on September itself. Entire Tamilnadu including south TamilNadu & interiors will get good & decent rains during this month. North coastal & Delta districts should be on vigil.
